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This is to certify that the

thesis entitled

MATERIAL OTHER THAN GRAPE (MOG)

IN JUICE AND WINE

presented by

PAO-JUI DAVID HUANG

has been accepted towards fulfillment
of the requirements for

M. s. degreein FOOD SCIENCE

 

 

 

June 4, 1979

   
   

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MATERIAL OTHER THAN GRAPE (MOG)

IN JUICE AND WINE

By

Pao-jui David Huang

A Thesis

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Food Science

1979

ABSTRACT

MATERIAL OTHER THAN GRAPE (MOG)
IN JUICE AND WINE

By

Pao-jui David Huang

MOG has historically caused operational problems at the proc-
essing plant and it seems very likely that it will also create juice
and wine quality problems.

Two grape cultivars, Concord grapes and Aurora Blanc were used
for grape juice and wine production, respectively. Grape samples taken
from the mechanical harvesters were analyzed for total weight of M06
and percent MOG. Hand-picked samples were used as controls and also
for the additions of varied amounts of M06 during processing in order
to determine the effect of M06 on the overall quality of finished pro-
ducts. Chemical and physical analyses of samples which evaluated the
quality included: (1) Total phenolic compounds and various phenolic
fractions. (2) pH and total acidity. (3) Brix. (4) Color. (5) Al-
cohol content. (6) Sensory assessment.

This study indicated that MOG content has a definite affect on the
chemical constituents and final quality of juice and wine. The total
phenolic, flavonoid and tannin contents of wine and juice increase as

MOG content in the harvested grapes increases.

to my father and mother

ii

ACKNOWLEDGEMENTS

I am sincerely grateful to Dr. J.N. Cash for his most valuable
guidance and never-ending patience, understanding and encouragement
throughout the course of this study and the preparation of this manu-
script.

Grateful appreciation is also expressed to the other members of
my guidance committee, Drs. P.C. Markakis, G.S. Howell, and M.A.
Ubersax, for their helpful suggestions.

Special thanks to Paw Paw Grape Juice Company and Warner Vineyard,
Inc., and National Grape Cooperative and welch's Foods for their gener-
ous supply of grapes used in the study.

Acknowledgement is extended to the Michigan Viticultural Advisory
Committee for their partial financial support of this work.

Finally, I am most grateful to my parents, sisters, and brother for

their encouragement during my graduate program.

iii

LIST OF TABLES . .

LIST OF FIGURES .

INTRODUCTION . .

LITERATURE REVIEW .

Phenols and Related Substances Other than Flavonoids

Flavonoids .

Amount and Distribution of Phenols in the Grape

The Role of Phenolic Compounds in Juice and Wine
Organoleptic Tests

TABLE OF CONTENTS

Effects of Machine Harvesting on Juice and Wine Quality

MATERIALS AND METHODS

Sample Preparation

Total Phenolic Compounds Determination
Flavonoid and Non-flavonoid Phenol Determination
Tannin and Non-tannin Determination

pH and Total Acidity Analysis

Color Analysis

Alcohol Content Analysis

Sensory Assessment

RESULTS AND DISCUSSION

White Wine Analysis

Concord Juice and Red Wine Analysis

SUMMARY AND CONCLUSIONS

iv

Page
vi

viii

12

13
16
18
18
21
22
23
24
25
25
25
27
27
42

60

Page
APPENDICES O O O I O O O O O O O O 61

I. Gallic Acid Standard Curve . . . . . . 61
II. Grape Juice Taste Panel . . . . . . . 62
III. Wine Taste Panel . . . . . . . . . 63

LIST OF REFERENCES . . . . . . . . . . 64

10.

11.

12.

13.

14.

LIST OF TABLES

Page

Material other than grapes (MOG) in mechanically

harvested grapes . . . . . . . . . . 27
Aurora Blanc must and wine analyses of all treatments at

various stages of fermentation . . . . . . 28
The soluble solid and alcohol content of white wine in

final stage of fermentation . . . . . . . 29
Analysis of phenolic fraction of white wine from hand

harvested grapes at various stages of production . . 30
Analysis of phenolic fraction of white wine from hand

harvested grapes with 1% leaf added . . . . . 31
Analysis of phenolic fraction of white wine from

mechanically harvested grapes at various stages of

production . . . . . . . . . . . 32
Analysis of phenolic fraction of white wine from

mechanically harvested grapes with 1% leaf added . . 33
Analysis of phenolic fraction of white wine with different

treatments at the time of grape harvest (9/12/78) . 35
Analysis of phenolic fraction of white wine with different

treatments after one month of fermentation (10/31/78). 36
Analysis of phenolic fraction of white wine with different

treatments after 2 months of fermentation (11/3/78) . 37
Analysis of phenolic fraction of white wine with different

treatments after 4 months of fermentation (2/7/79) . 38
Analysis of variance mean square for sensory attributes of

white wine . . . . . . . . . . . 39
Mean and standard deviation of the quality characteristics

for sensory evaluation (white wine) . . . . . 41
Mean and standard deviation of the quality characteristics

for sensory evaluation (white wine) . . . . . 41

vi

15.
16.

17.

18.

19.‘

20.

21.

22.

23.

24.

25.

Page

Concord juice and wine pH and total acidity . . . .
Brix and alcohol contents of red wines . . . . .

Color measurement of Concord juice in different
treatments 0 O O O O O O O O O 0

Color measurement of red wine with different treatments
after 1 month fermentation . . . . . . .

Color measurement of red wine with different treatments
after 2 months fermentation . . . . . . .

Analysis of phenolic fraction of Concord juice in different
treatment 8 O O O O O O O O O O 0

Analysis of phenolic fraction of red wine after 3 months
fermentation . I . . . . . . . . .

Analysis of phenolic fractions of Concord wine after 5
months fermentation . . . . . . . . .

Analysis of variance mean squares for sensory attributes
Of red Wine 0 O O O I O O O I O 0

Means and standard deviations of certain quality character-
istics for sensory evaluation of red wine . . . .

Means and standard deviations for sensory evaluation of
astringency and bitterness in red wine . . . .

vii

44

45

46

47

48 .

49

50

51

54

55

S6

LIST OF FIGURES

The effect of pH on anthocyanin color and structural

Mean of flavor strength for sensory evaluation of Concord

Mean of flavor acceptability for sensory evaluation of

Figure
l. Catechins (Flavan-3-ols) .
2. Three common catechins (flavonols)
3. Three common flavones .
4. Five minor aglycones . .
5. A dimer leucoanthocyanin .
6. A typical ellagitannin structure .
7. 2-Phenyl-benzopyrylium.(flavylium)
8. Six common anthocyanidins
9.
transformations . .
IO.
juice . . . . .
11.
Concord juice . . .
12.

Mean of astringency for sensory evaluation of Concord juice

viii

Page

10

ll

15

57

58

INTRODUCTION

In recent years mechanical harvesting has become a predominant
method for harvesting grapes. The effects of mechanical harvesting on
juice and wine quality are complex and result from the interaction of
many factors; including operating parameters of the harvester, the
specific grape variety, the extent of berry damage and the level of in-
corporation of MOG (Material Other than Grape). MOG has historically
caused operational problems at the processing plant and it seems very
likely that it will also create juice and wine quality problems.

Two grape cultivars, Concord and Aurora Blanc were used for grape
juice and wine production, respectively. Grape samples taken from the
mechanical harvesters were analyzed for total weight of MOG and percent
MOG. Hand—picked samples were used as controls and also for the addi-
tions of varied amounts of MOG ranging from 1 to 57. during processing
in order to determine the effect of MOG on the overall quality of finish-
ed products. Chemical and physical analyses of samples which evaluated
the quality included:

(1) Total phenolic compounds and various phenolic fractions.

(2) pH and total acidity.

(3) Brix.

(4) Color.

(5) Alcohol content.

(6) Sensory assessment.

2
The purpose of this study was to find the relationship between MOG

content and the wine and juice quality.

LITERATURE REVIEW

Phenols and Related Substances Other than Flavonoids

l. Derivatives of Hydroxylated Benzoic Acid

In the late 1800's, chemical preservatives were added to many foods,
including wine. Among these preservatives were salicylic acid, p-
hydroxybenzoic acid and the esters of these compounds. Ash (1952)
states that 90% of the wine made in 1900 in California had salicylic
acid added but most such additions are now prohibited in the major wine-
producing and wine-importing countries. Pellet (1906) identified small
amounts of salicylic acid which occurred naturally in grapes and un-
treated wine. Traphagen and Burke (1903) reported the equivalent of at
least 0.32 mg of salicylic acid per kg of fresh Concord grapes while
Chelle (1925) concluded from his work that small amounts of salicylic
acid can occur naturally in wine. RiHereau-Gayon (1963) reported finding
very small amounts of salicylic acid in some wines but other researchers
(Webb 1962; Stevens gtugl, 1967) indicated that this acid does not occur
in many wines. It appears certain from available data that natural sali-
cylic acid can be no more than 1 mg/liter, either free or readily
liberated by alkali in grape must or wine.

Guimberteau and Portal (1961) reported 0.2 to 0.5 mg per liter of
hydroxybenzoic acid in saponified samples of all the 18 wines and 4
juices they tested. RiHereau-Gayon (1963) indicated vanillic, syringic,
gentisic, protocatechuic, and gallic acid were detected in wine after

3

4
saponification. It seems possible that some degradation of flavonoids

of the alkaline-fusion and cleavage type was occurring during saponifica-
tion, so that the syringic acid may have come from malvidin residues,
vanillic acid could have come from peonidin and gallic acid from delphini-
din. Boettinger (1901) reported protocatechuic acid in the water-

soluble substance from grape leaves.

2. Derivatives of Hydroxycinnamic Acid

Simple observation shows that grapevines produce grapes which con-
tain anthocyanins and that the vines are lignified. Therefore from.our
knowledge of the biosynthesis of such compounds it seems very likely
that shikimic acid and cinnamates should occur in grapes and indeed,
several researchers (Kliewer 1966; RiEereau-Gayon 1963) have identified
these compounds in grape juice and wine. Caffeic acid and p-coumaric
acid, or their derivatives, as well as, ferulic and sinapic acid have
been reported in grapes and wine by several researchers and there can be
little doubt of their general presence (Hennig and Burkhardt, 1957, 1958).
Masquelier andeicci (1964) found chlorogenic acid, while Pifferi (1965)

indicated that both chlorogenic and isochlorogenic acid occurred in wine.

3. Other Nonflavonoid Phenols

Since tyrosine is a cinnamic acid precursor, it would be expected to
occur in grapes and wine and several investigators have shown this to be
the case (Castor 1953; Beridze and Sirbiladze, 1964; Nassar and Kliewer
1966). Free tyrosine occurs in grapes at about 20-60 mg/kg fresh weight,
but 75-90% of this disappears during fermentation to wine through conver-
sion to tyrosol by yeasts (Ehrlich 1907). Lingens 3; 31. (1967) indicated

that yeast does not require an external source of phenylalanine, tyrosine,

5

or other benzenoid substances, but is capable of synthesizing tyrosol
without the presence of these compounds. Yamamoto ggugl. (1966) report-
ed the yeast fermentation of a prepared medium containing L-tyrosine
produced. In addition to tyrosol, p-hydroxybenzoic acid, p-hydroxy-
phenyllactic acid, p-hydroxyphenylacetic acid, p—hydroxybenzaldehyde
acid or p-hydroxyophenylacetaldehyde, and p-hydroxyphenylpyruvic acid.
Chaudhary £3 31, (1968) reported gas chromatographic detection of a
trace of phenol itself in extracts of wines. They reported mecresol,
vanillin, sinapaldehyde, coniferadehyde, and syringaldehyde in wine, but
they thought these compounds may have been extracted from.wooden cooper-
age, or converted from lignin which was extracted from wooden cooperage.
Hennig and Burkhardt (1958) used two dimensional paper chromatography
to identify ellagic acid and ellagitannins in red and white wines. They
also found ellagic acid in large amounts in juice, but noted that it
could have been produced by polyphenoloxidase action on natural tannins
during the analysis. Ellagic acid was reported (Hennig g£_§1, 1958) in
large amounts in young wine fermented in the presence of grape solids, but

it was removed by aging and processing.

Flavonoids
The yellow flavonoids comprise a diverse, almost ubiquitous class

of pigments, with chemical structures similar to the anthocyanins.

Approximately 400 flavonoids are known and more are being identified.
These can be divided into the following families:

1. Catechins (F1avan—3-ols) and Flavones

6

The natural flavan-3-ol series is d-catechin itself.

 

Figure 1. Catechins (F1avan-3-ols)

Catechins (flavonols) are the most common and comprise the major

group in this family which includes kaempferol, quercetin and myricetin.

 

Kaempferol Quercetin Myricetin

Figure 2. Three common catechins (flavonols)

Flavone is less common and includes compounds such as apigenin,

luteolin, and tricetin.

 

Apigenin Luteolin Tricetin

Figure 3. Three common flavones

7
Sixty other aglycones, based on hydroxy derivatives of the flavon-
oid and flavone structure are known. Five other minor groups are known
and these are chalcones, aurones, flavanones, isoflavanones, and bi-

flavonyls.

Isoflavanone

 

Biflavonyl (Amentoflavone)

Figure 4. Five minor aglycones

Usually aglycones exist in the glycoside form with glucose, rhamnose,
galactose, arabinose, xylose, apiose, or glucuronic acid. The sites of
substitution are varied, but the 7; 5; 4'; 7,4'; and 3' positions are
common. The flavonoid compounds also may occur with acyl substituents in

a manner similar to the anthocyanins.

2. Leucoanthocyanins

Although leucoanthocyanins are colorless, under some food handling
and processing conditions, they can be converted to colored products.
The leucoanthocyanins have some alternate names, such as proanthocyanid-

ins, anthoxanthins, anthocyanogens, flavolans, flavylans and flavylogens.

8
The basic building block of leucoanthocyanins is f1avan-3,4-diol
which usually forms a dimer through a 4-8 or 4-6 linkage, but trimers
and higher polymers are not too uncommon. When a leucoanthocyanin is
heated in the presence of a mineral acid, it will product an antho-

cyanidin, such as pelarogonidin, cyanidin, petunidin or delphinidin.

 

OW! CH1

 

Flavan-3,4-diol

Leucoanthocyanin

Figure 5. A dimer leucoanthocyanin

The leucoanthocyanin compounds are of interest in wine and juice
because they contribute to the astringency or puckeriness and the flavor
of the product. They also contribute to enzymatic browning in wine,
because orthodihydroxy phenols can be oxidized to orthoquinones, which
then polymerize to brown melanin pigments. Leucoanthocyanin compounds
can also cause haze formation when the wine is chilled but this haze

will usually reclear when the wine is warmed.

3. Tannins
The term tannin, as well as tannic acid, gallotannic acid, and
incorrectly digallic acid, is defined in the Merck Index as a complex

mixture found in the bark of oak, sumac, and myrobalen. Its appearance

9

ranges from light yellow to brown in color. Tannic acid, as purchased
from a chemical supply house, has the formula C76H52046, a molecular
weight of 1,701 and probably consists of nine molecules of gallic acid
and one of glucose.

The term "tannin" as used in foods includes two types of compounds.
The first type is the condensed tannin which may be 4,8 or 2,8 C-C dimers
or 3,3-ether-linked dimers of catechin and related compounds. Other
linkages, such as 2-carbon, 7-oxygen or 4-carbon, 7-oxygen compounds
have been reported. The second type are the "hydrolyzable tannins"
including the gallotannins and the ellagitannins which are both polymers
of gallic acid and ellagic acid. A typical ellagitannin containing

gallic acid, ellagic acid, and one molecule of glucose is shown in the

following structures.

 

 

HC-O'-C
+1... 3
l _
l

liC-JD-
\ /
H Hf-O‘A b
H Ana-cu,
H \ / g

Gallic acid Ellagic acid Chebulagic acid

 

 

 

Figure 6. A typical ellagitannin structure

10
Although both types of tannins may exist in food, the tannins of

grapes and wine have been known for many years to be condensed tannins
(Thudichum and Dupfe, 1872; Dekker, 1913). When Pointe and Gualdi (1931)
used formaldehyde and hide powder on wine they obtained equal precipi-
tates with each solvent so they concluded that the true tannins of wine
were all of the flavanol-derived condensed type. Since oak gallotannic
acid may be added to wine under certain processing conditions, it might
be found in wine, but tannins of the pentadigalloyl glucose type or any
other of the hydrolyzable tannin types do not occur naturally in wine or
grape juice. Both types of tannins contribute to enzymatic browning

reactions, but their mechanisms of action are not well understood.

4. Anthocyanins
Anthocyanins are glycosidic forms of anthocyanidins (aglycones),
whose basic skeletal structure is derived from.the flavylium nucleus

(2-pheny1-benzopyrylium).

  

Figure 7. 2-Phenyl-benzopyrylium (flavylium)

Only five sugars have been found as portions of anthocyanin molecules.
They are in order of relative abundance glucose, rhamnose, galactose,
xylose, and arabinose. Anthocyanins may also be "acylated" which adds a
third component to the molecule when one or more molecules of p-
coumaric, ferulic, caffeic, or acetic acids may be esterified to the

sugar molecule.

11

Twenty anthocyanidins are known but only six, pelargonidin,

cyanidin, delphinidin, peonidin, petunidin, and malvidin are important

in foods.

 

Petunidin Peonidin

Figure 8. Six common anthocyanidins

Rice (1965), in paper chromatographic studies of Concord grape pig-
ments, found cyanidin, peonidin, delphinidin, petunidin, and malvidin
monoglucosides, diglucosides, and in most cases one or more acylated forms
for each glucoside. Shewfelt (1966) found 14 paper chromatographfl: spots
of pigments in concord grape juice, and the aglycone proportions were
45.72 delphinidin, 37.12 cyanidin, 8.82 petunidin, and 8.42 malvidin.

The anthocyanins of wine would be expected to be the same as those
of grapes, and if the wines are young enough this may be true. The acyl
groups are hydrolyzed very readily and will rapidly disappear from link-
age in anthocyanins and appear as free acids in the wine. The glycosides
have been shown to hydrolyze to free anthocyanidins, and anthocyanogens

I
which have been reported to give cyanidin in wine (Ribereau-Gayon'gghgl,

12
1958). Very little anthocyanidin can usually be recovered from.wine,
and the major change appears to be the incorporation of anthocyanidins

into polymeric red, tannin-like molecules.

Amount and Distribution of Phenols in the Grape

Usually hand picked grapes are harvested by cutting entire clusters
from the vines and the harvested weight of fruit includes the cluster
stems which are removed during preparation of the grapes for wine and
juice. Mechanical harvesting, which has become a predominant harvest
method, usually involves some type of vine agitation to shake the berries
from the rachises and a vibrating chain belt to separate the stems,
petioles, leaves and canes from the harvested fruit (Black and Cargill
ggngl. 1977), but this method leaves many stems, petioles and leaves in
the product and these materials have a relatively high phenol content.

In 7 varieties, Amerine and Bailey (1959) found 2,400 to 21,900 mg phenol,
calculated as tannic acid, per kg of fresh weight of main stem, and 9,100
to 43,700 mg/kg in lateral stems. Durmshidze (1955) reported "tannin" to
be 40,000 mg/kg of the dry weight of grape stems, and 20,000 mg/kg of the
leaves. Diemair £3 31, (1951) reported 1320 - 3600 mg tannin per kg in
fresh leaves and 1040-2200 mg/kg in their stems.

Singleton and Esau (1969) indicated that a ton of grapes contains an
average of 3.7% stems, with the remaining 96.3% representing the typical
berry weight. If all the tannin of the stem was extracted and dissolved
in the juice or wine produced from the ton of grapes it could contribute
from 90 to 1700 mg of phenol/liter, calculated as gallic or tannic acid
with an estimated average of 1000 mg/liter. In this situation the stems
could be a very significant source of phenols if they were not completely

removed before processing operations begin. Another reason the stems

13
should be removed is because they contribute to off flavor and adsorb
anthocyanins which reduces the color (Pacottet, 1904; Laborde, 1910).
Singleton (1966, 1967) concluded that the total phenol of the berry was
distributed, on the average, about 1% in the solid pressed pulp, 52 in
the juice, 50% in the skins for red varieties and 252 for white, and the
remaining 46-692 in the seeds. But he added for any specific sampling
of grapes, actual analysis would be necessary owing to considerable vari-
ation by variety, vineyard, year and processing technique. The following
table presents values considered typical for the amount of total phenol
calculated as gallic or tannic acid in the major fraction of the grape

berry (Singleton ethal, 1969).

Table 1. Total Phenol Distribution in Vitis vinifera Wine Grapesa

 

_4

 

Portion Red varieties White varieties
Skins 1859 904
Pressed pulp 41 35
Juice 206 176
Seeds 3525 2778
Total 5631 3893

 

aIn gallic or tannic acid equivalents, mg/kg berries.

The Role of Phenolic Compounds in Juice and Wine Organoleptic Tests

1. Flavor Effect

Although it is often assumed that phenols only contribute bitterness
and astringency to grape juice and wine, this is not always the case and
the presence of phenolic compounds in these products may be very desirable

because they can give body and fullness of flavor. The materials which

14
are most likely to be responsible for astringency are the small poly-
meric, yet soluble tannins and the leucoanthocyanins, while bitterness
is a property of many substances in addition to some phenols (Bate-Smith
55.31, 1953). It is generally agreed that some level of astringency and
bitterness is desirable in red wine, but it is not very clear what that
level should be or how it can be defined. The astringency of tannin is
proportional to its protein-binding capacity, which may change with
storage. Joslyn and Goldstein (1964a) indicated that a tannin content
of 200 mg/liter is necessary for detection in wine or juice and increases
above 200 mg/liter must be greater than 40 mg/liter increments to be
detectable.

It is generally recognized that the loss of astringency during
fruit ripening is related to increased polymerization with decreased
solubility of the tannin (Joslyn and Goldstein, 1964a) and this loss
of astringency leads to tastelessness, rather than bitterness. Depoly-
merization, such as conversion of a polymeric anthocyanogen to antho-
cyanidins, may also lead to loss of astringency. These observations
are consistent with astringency being dependent upon protein-binding
capacity, because the simple flavonoids bind protein poorly, conversely,
large condensed tannins bind protein easily, which causes precipitation
and the larger the tannin molecule the greater the precipitation. It
appears that astringency can be produced by polymerization of small
phenolic molecules to larger ones or by breaking up very large molecules
to smaller ones, although either of these mechanisms may also cause a
loss of astringency, under certain conditions. Maier gt 31.(l964)
mentioned that polymerization by oxidative or other mechanisms might
produce increased astringency as molecular weight increased, and then

decreased astringency as the optimal astringency size was exceeded.

15

2. Color

Appearance is an important feature of wine, and a wine's color,
along with clarity, is a good indicator of its past history, condition,
and probable present and future quality. The colors of most wines are
almost wholly the result of their content of various phenolic substances.
The substances responsible for the yellow colors of white wine were
thought for many years to be flavonols, particularly quercetin, based
largely on the fact that quercetin was the only known wine-soluble yellow
substance identified in grapes (Genevois, 1951). The color of red wine
may vary visibly in intensity from very pale rose to dark so as to appear
nearly black. This hue depends upon factors such as pH, co-pigmentation,
metallic lakes which affect the anthocyanins themselves, and upon the
amount of brown color coexisting in the wine. The major effect of pH
on anthocyanin color and structural form has been clarified by Jurd
(1963) and Geissman (1963). In the pH range of 2.0 to 6.0 the flavylium

salts evidently undergo the following transformations:

 

Figure 9. The effect of pH on anthocyanin color and structural
transformations

16

Many other factors may also influence visable color. Sulfur dioxide
tends to prevent browning, and bleaches not only some of the brown color
but anthocyanins asunfll. lfimre are a number of reports that the presence
of tannin intensifies the red color of wine or juice and shifts it
slightly toward blue (Winkler and Amerine, 1938). Gallic Acid has been
reported to have a similar, but weaker effect. In the presence of metal
ions such as aluminum and iron, complexes between other phenols, the
metal, and anthocyanins modify the color exhibited, often in the blue

direction.

Effects of Machine Harvesting on Juice and Wine Quality

The effects of mechanical harvesting on juice and wine quality are
complex and result from the interaction of many factors, including
operating parameters of the harvester, relative vine vigor, trellising
practices, the specific grape variety, the extent of berry damage and
the incorporation of material other than grapes (MOG), such as canes,
bark, petioles, and leaves. There have been few papers published deal-
ing with the effect of MOG content on juice and wine quality.

Petrucci and Siegfried (1975) reported the cultivars Ruby Cabernet
and Emerald Riesling were mechanically harvested and analyzed for MOG
content. Emerald Riesling, which harvested comparatively easily, had a
low MOG content and a small variation in MOG content between samples.
Ruby Cabernet had a higher MOG content and a greater variation in MOG
content between samples but in both cultivars, about half of the total
MOG was small leaf fragments which would adhere to the grapes and not be
easy to remove before processing.

Johnson and Grgich (1975) compared the quality of White Riesling

and Cabernet Sauvignon wines from grapes harvested; (A) by conventional

l7
'handpicking and handling methods and; (B) by Redwood's Up-Right Vectur

mechanical harvester which gave a MOG content of less than 12. For
Cabernet Sauvignon the wine from the machine-harvested grapes had identi-
cal characteristics to the wine from the handpicked grapes. For White
Riesling, the machine-harvested grapes arrived at the winery free from
oxidation, had fewer leaves than the handpicked, and yielded a wine with
superior fragrance and slightly higher acidity. The must from the hand-
picked grapes was slightly higher in sugar content.

Noble and Ough‘ggngl, (1975) investigated the effects of added
grape leaves, berry damage, and mechanical harvest on wine quality. The
results indicate that there were overall adverse effects on wine quality
from mechanical harvesting of grapes'or from adding shredded grape leaves.
In all cases, the white wines made from damaged or machine-harvested
grapes, or from grapes to which leaves had been added, were significantly
darker by visual assessment as well as by absorbance at 420 nm. The
phenolic content of wines increased with the addition of leaves or with

berry damage.

MATERIALS AND METHODS

Since MOG content seems to be correlated with ease of harvest and
the quality of both juice and wine, two cultivars which differ markedly
in harvestability and final product characteristics were used for
quality evaluations. Samples taken from mechanical harvest were analyz-
ed for total weight of MOG and per cent MOG. Handpicked samples were
used as controls and also for the additions of varied amounts of MOG
during processing in order to determine the effect of MOG on the overall
quality of finished products. Chemical and physical analyses of samples
included:

(1) Total phenolic compounds and different phenolic fractions

(2) pH and total acidity

(3) Brix
(4) Color
(5) Alcohol

(6) Sensory assessment

Sample Preparation:

During the 1978 harvest, concord grapes for grape juice and red
wine production and Aurora Blanc grapes for white wine production were
supplied by Welch's Inc. and Warner Vineyards, respectively.

Aurora Blanc grapes were harvested by two methods, (a) by conven-
tional handpicking and (b) by mechanical harvester. The mechanically

harvested grapes were stored in a cold room (40 C) for approximately

18

19

12 hours. Green and senescent leaves were obtained from the vines
which were hand harvested. weighed amounts of leaves, which were
shredded by hand were added to weighed amounts of hand harvested grapes
to give 1% (W/W) of added leaf tissue (HH + 1% leaf). Intact, hand
harvested (HH) grapes served as the control.

For mechanically harvested grapes, the MOG content was determined
on five, 2000 gram samples. Shredded leaf tissue was added to mechani—
cally harvested grapes to give 12 (W/W) added leaf (MH + 1% leaf)

while mechanically harvested (MH) samples served as the control.

White Wine Making Procedure:

All mechanical and hand harvested treatments were held overnight
at 21-24OC, then crushed and de-stemmed and 100 PPM sulfur dioxide was
added to sterilize the crushed grapes (must). Juice was pressed and
filtered through cheese cloth into fermentation containers where sugar
and acid content were checked and the sugar was adjusted to 220 Brix.
Saccharomyces cerevisiae--Montrachet yeasts were added to the must,
approximately 36 hours after the addition of sulfur dioxide and the
fermentors were placed in a 10 to 15.50C cubicle for fermentation.

When fermentation was complete (approximately 20 days) the sugar level
was 6.00 Brix and the acidity was around 0.65%. The wine was racked and
topped off, then stored for 3 months at 10°C before bottling. Samples
were taken during different stages of fermentation and analyzed for
acidity, sugar, alcohol and phenolic content.

In early October, 1978, Concord grape samples were obtained by
conventional handpicking and from covered grape gondolas which had been
harvested by a mechanical harvester. Green and senescent leaves and

petioles, stems and rachis were obtained from the vines which were hand

20

harvested. Weighed amounts of each of these were added to weighed
amounts of handpicked grapes to give the following treatments: (1) hand
harvested (HH) grapes (2) hand harvested grapes plus 1% leaves and 1%
petioles (3) hand harvested grapes plus 5% leaves and 5% petioles (4)
hand harvested grapes plus 1% leaves (5) hand harvested grapes plus 5%
leaves (6) hand harvested grapes plus 1% petioles (7) hand harvested
grapes plus 5% petioles.

For mechanically harvested Concord grapes, five-2000 gram samples

were checked for their MOG contents.

Concord Grape Juice Making Procedure:

Samples of the various treatments were crushed and destemmed before
heating to 68-70°C where they were held for 2 minutes to inactivate
enzymes and facilitate the extraction of pigment. The samples were then
cooled to 45-50°C and commercial pectinase (Irgazyme from Ciba-Geigy
Corp.) was added to hydrolyze pectins. These batches were held for 18
hours at 21°C, then pressed. The juice was collected in plastic contain-
ers which were covered and refrigerated for detartration. After 3-4
weeks, the detartration process was complete and the juice was pasteurized,
bottled and stored. Samples of the juice were analyzed for the phenolic

fractions.

Concord Red Wine Making Procedure:

Samples of grapes from.each of the various treatments were crushed
and destemmed. The must was sterilized by adding 125 ppm sulfur dioxide
and then refrigerated for approximately 24 hours. Sugar and acid content
was adjusted to 220 Brix. After 24-36 hours the sulfur dioxide had dissi-

pated sufficiently and a montrachet strain of SaCcharomyces cerevisiae

21
was added to the must in a plastic primary fermentor which was then
covered with cheesecloth. The must was stirred twice a day for four
days to aerate the mixture and break the cap of floating pomace. The
free run wine was drawn off and the pulp was pressed in a pilot plant
juice press. The wine was placed in secondary fermentors with fermenta—
tion locks and held for three weeks at 25-30°C before the first racking.
After racking the wine was stored for approximately three months before
it was filtered and bottled. At different times during the fermentation
and holding periods, samples were removed and checked for pH, titratable

acidity, sugar content, alcohol content and analyzed for phenolic content.

Total Phenolic Compounds and Different Phenolic Fractions:
Total Phenolic Compounds: ‘

Total phenolic compounds were determined according to the method of
Singleton and Rossi (1965) with the following modifications:

(1) For white wines, 0.5 ml sample plus 65 mls of distilled
water were placed in a lOO-ml volumetric flask. Red wines
and juice were diluted 1:3 with distilled water then 0.5 m1.
diluted sample plus 65 mls of distilled water were placed in
a lOO-ml volumetric flask.

(2) 5 mls of Folin-Ciocalteu reagent were added and mixed
thoroughly.

(3) 15 mls of 20% sodium carbonate solution were added and the
solution was made to 100 ml volume.

(4) Solutions were left standing for 2 hours at room temperature

to fully develop the color.

(5) Absorbance was read at 765 nm.

22
(6) Total phenolic content was calculated (as gallic acid) from
a standard curve (Appendix I).

The Folin-Ciocalteu reagent consists of a yellow acidic solution
containing complex polymeric ions formed from phosphomolybdic and phospho-
tungstic heteropoly acids. This reagent oxidizes phenolates and the
heteropoly acid becomes partially reduced from the +6 to a mixture of +6
and +5 valence states, resulting in the production of complex molybdenumr
tungsten blue. Complete reduction to the lower valence state destroys
the color. The phenols are oxidized rapidly only in solution sufficiently
alkaline to give appreciable concentrations of the phenolate ions. Most
phenols are about 50% ionized at pH 9-10 but as the ionized portion
reacts with the Folin reagent the equilibrium will shift and more pheno-
late will be produced. Time would be required for this reaction to

approach completion.

Flavonoid and Nonflavonoid Phenol Determination:

Total phenolic compounds in wine can be generally separated into
flavonoid and non-flavonoid phenols. Therefore, if the total and non-
flavonoid phenolics can be accurately determined, the flavonoid content
can be calculated very easily. The quantitative estimation of flavonoid
and non-flavonoid phenols (Kramling and Singleton, 1969) in wine is
based upon the determination of the phenol content before and after
precipitation and removal of the flavonoids through reaction with forms
aldehyde under selected condition as follows:

(1) 10 mls of wine were pipetted into a 30 ml test tube, then

10 m1 of 1:4.conc. HCl added.
(2) 5 m1 of a standard formaldehyde solution contain 8 mg/ml were

added, sparged with nitrogen and stoppered.

(3)

23

Samples were incubated 24 hours at room temperature then
filtered through a membrane filter of 0.45 u pore size. Under
these conditions the filtrate contained only non-flavonoid
phenols because phenols lacking a meta-dihydroxy grouping (non-
flavonoid) did not precipitate. The non-flavonoid phenol
content could then be tested with the Folin-Ciocalteu reagent

and measured colorimetrically.

Tannin and Nontannin Determination:

Precipatation of tannins with cinchonine sulfate was carried out

according to the method of Peri and Pompei (1971) and adapted to wine as

follows:

(1)

(2)

(3)

(4)

(5)

(6)

A 50 ml sample was placed in a 100 m1 centrifuge tube and
neutralized to pH 7.0 with sodium hydroxide solution.
Precipitation was carried out by the addition of 25 ml of

pH 7.9 phosphate buffer and 12.5 ml of the cinchonine sulfate
solution (1.5 g cinchonine base, 2 ml 1:3 sulfonic acid,
water to 100 ml.).

After 20 minutes at room temperature the cinchonine tannate
precipitate was separated by centrifuging and the clear super-
natant was transferred to a 200 ml volumetric flask.

The precipitate remaining in the centrifuge tube was washed
twice with 10 ml of a 10% solution of sodium sulfate in water.
The supernatant together with the washing, was acidified to pH
3.5 with HCl, brought to volume with distilled water, and used
for the determination of nontannin phenolics with the Folin-
Ciocalteu reagent.

The cinchonine tannate precipitate was dissolved in ethanol-

24
10% HCl, brought to 50 ml with the same solvent, and used
for the determination of tannin phenolics with the Folin-
Ciocalteu reagent.
Each analysis was replicated twice and mean data were reported.
The results obtained were double checked by carrying out the pre-
cipitation with cinchonine and formaldehyde on two different portions
of the same wine. The fractionation mechanism may be schematized as

follows:

Wine
(TOTAL PHENOLICS)

Cinc onine
precipitation

 

J? 7%
Prec pitate Supernatant
(nontannin henolics)
Solution in

 

EtOH 10% HCl Formaldehyde
(TANNIN PHENOLICS) precipitation
Superngtant

(NONFLAVONOID PHENOLICS)
Precipitate

(NONTANNIN FLAVONOIDS,
by difference)

pH and Total Acidity:
The juice and wine pH and total acidity were measured with a pH
meter as follows:
(1) 10 ml of sample and 75 ml distilled water were transferred to
a 250 m1 beaker.
(2) The pH of the samples was taken then they were titrated with
0.1N sodium hydroxide to the phenolphthalein endpoint of 8.1

with the pH meter.

25

(3) Per cent acidity was calculated as tartaric acid.

Color:

The color of Concord juice and wine was measured using a Hunter
Color Difference Meter, Model D25 with an inverted head. After standard-
izing with a pink tile, L-67.6, a-+21.4, b-+ll.9, a 50 m1 sample was
filled into an optical glass cylinder cup 3.5 inch x 0.75 inch and a
standard white plaque was placed under the bottom of the cup. Two
readings were taken on each sample and averaged to give individual means

for L, a, b values.

Alcohol Content:

The alcohol content of white and red wine was determined by dis-

tillation using the following procedure:

(1) 200 ml of the sample were placed in a 500 ml Kjeldahl flask
with 50 ml distilled water. The flask was connected to a
condenser and the wine was distilled to give 190 ml distillate
collected in a 200 ml volumetric flask.

(2) The 200 m1 volumetric flask was held in a water bath at 15.50C
and made to volume with distilled water, mixed and held until
the temperature had equilibrated.

(3) The sample was transferred to a cylinder and alcohol content
was determined with an alcohol hydrometer.

(4) Every sample was replicated and mean data were reported.

Sensory Assessment:
Panelists evaluated four white wines and nine red wines, and nine

Concord juice samples. These evaluations were carried out by 12

26

panelists who tasted the product each day for five different days.

All evaluations were made in individual booths under white light.
Samples were scored 10 points for each of the factors which included
flavor acceptability, aroma acceptability, aroma intensity, bitterness
and astringency (Appendix II, Taste Panel Ballots). All taste panel
data were analyzed for variance and Duncan's Multiple Range Test (1957)
was then used to pinpoint significant differences among variables

revealed by the analysis of variances.

RESULTS AND DISCUSSION

Table 1 shows the average weights of total MOG found in both culti-

vars of mechanically harvested grapes used in this study.

TABLE 1. Material other than grapes (M06) in mechanically harvested

 

 

 

 

grapes.
Total MOG (mean)
Variety No. of Samples Avg, Sample Wt. (g)? Wt. (g) %
Aurora Blanc 5 2,000 94 4.7
Concord 5 2,000 52 2.6

 

Mechanically harvested Concord grapes contained slightly more than half
the MOG that mechanically harvested Aurora Blanc grapes did. This prob-
ably reflects the inherent variability in ease of harvesting which exists

between the cultivars.

White Wine Analysis:

Table 2 presents the must analyses for all samples. With the longer
holding times, total acidity declined and pH increased in all samples.
These results are similar to those of Ough (1969), Ough.g£flgl. (1971) and
Noble and Ough (1975) who found changes occurring, due to longer skin
contact times. The pH of the final wine was related to the initial pH of
the must while the decrease in total acidity was due to tartrate precipi-
tation and subsequent removal of the precipitate during the fining

27

28
procedure. Adding leaf tissue to the hand harvested and mechanically
harvested grapes caused the pH to increase slightly. The ME, MH + 1%
leaf, and HH + 1% leaf samples did not differ significantly from.the
control sample (HH) in pH and total acidity.

TABLE 2. Aurora Blanc must and wine analyses of all treatments at
various stages of fermentation.

 

 

 

 

 

MUST WINE
,pH Total Acidity
Total

Treatment 4 hr. 24 hr. 4 hr. 24 hr. ApH Acidity
Hand Harvested 3.2 3.3 0.83 0.75 3.40 0.64
Hand Harvested

+ 12 Leaf 3.2 3.49 0.83 0.76 3.55 0.66
Mechanically 3.45 3.55 0.81 0.76 3.58 0.61

Harvested
Mechanically

Harvested + 1% 3.45 3.65 0.81 0.79 3.68 0.58

Leaf

 

The initial Brix of the hand harvested (HH) grapes differed somewhat from
that of the mechanically harvested (MH) fruit, reflecting slight differ-
ences in the maturity of the samples, but after adjusting the Brix and
fermenting the samples, Table 3 shows that final Brix and alcohol content
had very little difference in any of the treatments, which means that
adding small amounts of leaf tissue and MOG may not affect the fermenta-
tion processes. Even in the MH + 1% leaf, where the total phenolic
content was almost double that in the control sample (HH), (Table 11),
the yeast fermentation did not appear to be significantly inhibited.
Tables 4 through 7 present results of the analysis of the phenolics

in white wine made from HR, HH + 1% leaf, MH and MH + 1% leaf at various

29
time intervals during production. In all four treatments, the total
phenolic, flavonoid, and tannin contents decreased during wine processing.
This is probably due to the fact that parts of the flavonoids and tannins
precipitate with other substances, particularly potassium.bitartrate,
and is largely removed during fining and/or filtration. Also, during
the fermentation process, some of the small soluble tannin or flavonoid
compounds may polymerize to large insoluble polymers or they may form
insoluble complexes with proteins which then precipitate and decrease the
tannin, flavonoid and total phenolic contents.

TABLE 3. The soluble solid and alcohol content of white wine in final
stage of fermentation.

 

 

 

Final Wine Alcohol
Initial Adjusted Soluble Solid Content
Treatment Brix Brix (Brix) ‘(%)
Hand Harvested 13.0 22 6.0 13.4
Hand Harvested
+ 1% Leaf 13.8 22 6.0 13.0
Mechanically -
Harvested 15.0 22 6.2 13.1
Mechanically
Harvested + 1% 15.0 22.2 6.2 14.0

Leaf

 

30

OOH x

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mowaoaosm HmuOU

 

 

31

 

 

 

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32

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33

moaaoaoca Houou

 

 

 

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34

Tables 8 through 11 compare the phenolic fractions of the white
wine for each of the treatments at the same stage of production. The
addition of 1% leaf to hand harvested and mechanically harvested grapes
at the time of harvest, had little influence on the total phenolic,
flavonoid, and tannin contents at that stage. The MR and MH + 1% leaf
samples, however, had much higher total phenolic, flavonoid and tannin
contents than the HR and HH + 1% leaf samples, due to the leaching of
these materials from the MOG during the harvesting procedure. One month,
two months, and four months fermentation data (Table 9, 10, & 11) show
that in the MH and MH + 1% leaf samples, the total phenolic content is
still much higher than HH and HH + 1% leaf, but the difference in tannin
content continously decreased. After four months fermentation the
tannin contents of all treatments are very nearly the same. This indi-
cates that in MB and MH + 1% leaf samples the tannins precipitate much
more than in HH and HH + 1% leaf. It may be that MH and MH + 1% leaf
samples contained some MOG substance which caused tannins to precipitate
more easily.

Results for the analysis of variance for taste panel data are pre-
sented in Table 12. It should be noted that the values for replications
are not significant in any of these tables, indicating that the 12
panelists who tasted the samples and rated each of the various factors
every day for five different days were very consistent in their ratings.
The values for the factors of flavor acceptability, aroma acceptability,
and aroma intensity are significant at the 1% level, but astringency and
bitterness are not significant. The lack of significance for the last
two variables is probably correlated with the decreases in the tannin
content, since this compound is most likely to be responsible for

astringency and bitterness. Joslyn and Goldstein (1964a) has indicated

35

mowaonona Hmuou

 

 

 

 

 

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moHHoamsn Hmuou

 

 

36

 

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37

moHHocone Hmuon

 

 

 

 

 

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38

mOHHososa Hmuou

 

 

 

 

 

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39

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«

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.NH HHm¢H

40
that 200 mg tannin/liter is a minimum.detectable level and it can read-
ily be seen in Table 11 that the tannin content of any of the treatments
after fermentation is only about one fifth this amount. Flavor and
aroma in wine are also influenced by the phenolics of the MOG although
there are probably other MOG factors which also contribute to the sig-
nificant difference that the panelists noted in these components. Tables
13 and 14 show the taste panel means, standard deviation, and a compari-
son of the factors which were rated by the panelists. 0n the 1 to 10
scale used in this study, 10 indicates the most acceptable, 1 indicates
the least acceptable. In aroma acceptability, the panelists found
HH and HH +l% leaf to be definitely better than MH and MH better than
MH + 1% leaf but all the wines scored above 5 and were considered to
have acceptable aromas. In flavor acceptability, HH, HH + 1% leaf and
MH had the same level of acceptability and were definitely better than
MH + 1% leaf which scored in the unacceptable range. In aroma intensity,
the panelists found that HH had the strongest aroma, MH and MH + 1% leaf
had about equal aroma levels, and the aroma of the HH + 1% leaf seemed to
be the least intense of all the treatments. The panelists seemed to
indicate that wine made from the HR fruit had the best all around quality
but the addition of 1% leaf to the HR had only a small overall effect in
quality. Wine made from the MH grapes had a slightly lower quality than
either of the HH samples and the addition of 1% leaf to the MH fruit pro-
duced a wine that was significantly lower in quality than that made from

HH grapes.

41

Table 13. Mean and standard deviation of the quality characteristics
for sensory evaluation (white wine).

 

 

Aroma Flavor Aroma
Acceptability Acceptability Intensity

 

Hand Harvest 6.57a 1". 0.19 5.98‘:1 i 0.33 5.793 1'. 0.28

Mech. Harvest 5.9813 i 0.24 5.63a : 0.52 4.80b 2‘. 0.41

Hand + 12 Leaf 6.823 i 0.29 5.80“ i: 0.53 3.98° i 0.35

Mech. + 12 Leaf 5.26° i 0.35 4.67b i". 0.26 4.72b i 0.25

 

a“cAverage superscripted by the same letter are not significantly
different at the 5% level of probability (Duncan, 1957).

Table 14. Mean and standard deviation of the quality characteristics
for sensory evaluation (white wine).

 

 

 

Astringency Bitterness
Hand Harvest 6.152 0.40 7.158: 0.28
Mech. Harvest 6.138: 0.57 7.425“: 0.44
Hand Harvest + 12 Leaf 5.908: 0.24 7.123: 0.73
Mech. Harvest + 12 Leaf 5.908: 0.48 6.67ai 0.38

 

a-cAverage superscripted by the same letter are not significantly
different at the 5% level of probability (Duncan, 1957).

42
Concord Juice and Red Wine Analysis:

Table 15 shows the pH and total acidity (T.A.) data for all the
Concord juice and wine samples at various stages of processing. The
data shows that total acid declined and pH increased in all samples
before the first racking. These results are similar to those of Ough
g£_§1,(l971) and Nobel and Ough (1975) who observed similar acid and
pH changes in samples which had longer skin contact times and this is
possibly due to tartrate precipitation. After aging one month, the pH
decreased slightly and total acid increased slightly as compared with
the sample taken before the first racking. Table 16 shows that the
Brix and alcohol contents of the finished wine from.the nine treatments
did not differ appreciably, which would indicate that the various
amounts of MOG did not affect the fermentation process.

Tables 17, 18, and 19 present Hunter color measurements expressed

as L, +a, +b, hue (a/b) and saturation(a2+bz)1/2

of Concord grape

juice, wine after one month of fermentation, and after two months
fermentation, respectively. Objective color measurements have several
advantages over visual descriptions in specifying juice and wine color.
The "L" value, which measures lightness or darkness of a product,
actually describes the relationship between reflected and absorbed
light. The Hunter "a" value denotes redness in the "+" mode or green-
ness in the "-" mode, while the Hunter "b" value measures yellowness in
the "+" mode or blueness in the "-" mode. Hue is expressed by the angle
whose cotagent is a/b. Saturation is measured by the expression

(a2 + b2)“2

, which describes reflection at a given wavelength and
shows how much a color differs from gray. The L value, hue, and
saturation express the interdependence of these three color parameters,

and because of this, none of them used alone can give an accurate

43
description of wine but the combination of the three defines the
product very well (Robinson, 35.21, 1969). Comparing Tables 17
through 19, one can find no relationship between the color parameters
and the amount of MDG added in any of the samples, or between those
parameters and the amount of MOG added in any of the samples, or
between those parameters, and processing time in each treatment, which
simply means that MOG had little affect on the wine color in this
study. Table 20 shows the total phenolic content, flavonoid and non-
flavonoid content, tannin and nontannin content of all the nine differ-
ent treatments in Concord juice. The sample containing 5% leaf and
5% petiole, had the highest total phenolic, flavonoid, and tannin
content, followed in order by the 5% petiole, 5% leaf, MH (which both
contain 2.6% MOG), 1% petiole, HH (control sample), 1% leaf plus 1%
petiole, and finally the 1% leaf samples. These results generally
fit the experimental hypothesis which holds that a sample containing
higher MOG content will have higher total phenolic, flavonoid, and
tannin content. The two exceptions, 1% leaf and 1% leaf + 1% petiole
contained total phenolic, flavonoid and tannin levels below the control
sample but this may be due to some substance in the leaf tissue which
precipitates phenolic compounds in the wine. However, if a large amount
of leaf tissue is added, the phenolics in the leaf tissue may exceed
the small amount precipitated from wine so that the total effect is an
increase in phenolics. Tables 21 and 22 show the phenolic fractions
in Concord wine after three and five months of fermentation. It can be
readily seen that for each treatment, total phenolic, flavonoid and
tannin content all decreased, just as it did in the white wine and
probably for the same reasons. It should also be noted that the amounts

of the different phenolic fractions in the various treatments follows

44

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2.: 35 $5 a: 3... a: 35 35 «To 8.». a a:
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45

 

 

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47

 

 

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GOHumnsumm

 

 

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48

 

 

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49

 

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aOHumuHmHuoum maHaonoaHo

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:OHumummHomum owhnovaauom

 

 

 

 

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.muauauwmuu uaoumwMHv :H moHafi vuounoo mo :oHuomum oHHocmna mo mHthqu .om MHmda

50

00H

IN

mUHHocona Hagan
amOHHoamsm‘Haucu I AmuHHoaosm‘chcmu + moHHoamnmeHcaaulaoav “mm vmumHaoHao mm: Houuo unmoumn ushH

 

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51

moHHocmnm Hauou

 

 

 

 

 

=OHumuHmHomum oaHaosuaHo

GOHumuHaHuoum mvmnwvasuom

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Nn + uan Nm
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Nuouum Achcauv aancaulaoav HmcHoao>mev AmvHoco>mHuIcocv Hoaonm
muwuHaHooum uamumaumanm oumanHuoum ucmumaumnnm Hmuoa

 

 

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.NN mqm<H

52

the same pattern as seen in the Concord.juice, with.the higher MOG
samples containing higher total phenolic, flavonoid, and tannin contents.

Results of the analysis of variance of the sensory assessment data
for the Concord wine is shown in Table 23. The values for flavor acceptae
bility, aroma acceptability, bitterness and astringency are all signifi-
cant at the 12 level, but aroma intensity is not significant. These
results differ somewhat from.those found for the white wine, which did
not show significant difference in bitterness or astringency, probably
because of the tannin loss during fermentation. The red wine also lost
tannin during fermentation, however, the initial tannin content in the
Concord grapes was considerably higher than in the Aurora Blanc fruit
and a comparison of the tannin contents of the red and white wine after
fermentation will reveal that the red wine had considerably more tannin
than the white wine. The F ratio for replications within the categories
of flavor acceptability, aroma acceptability, bitterness, and astringency
are significant at the 51 level indicating that the panelists were some-
what less consistent in the ratings of the red wine than they were in
their ratings for the white wine. Tables 24 and 25 show the taste panel
means, standard deviations, and a comparison of means for the factors
which were rated by the panelist. In aroma acceptability, H3, MB, RB +
1% Petiole, and HH.+ 12 Leaf + 1% Petiole had almost the same level of
acceptability and were definitely better than EH + 52 Petiole, HH + 52
Leaf and HE +»52 Leaf + 5% Petiole. For flavor acceptability, the
panelists indicated that HE had the best flavor acceptability of all the
different treatments. In order of acceptability, ME, HH + 12 Petiole,
and HH + 12 Leaf + 1x Petiole were ranked next and were definitely

better than HH + 5% Petiole, and HH.+'SZ Leaf. The least acceptable

53
sample was the HH‘+ 52 Leaf + 52 Petiole. For astringency and bitter-

ness, panelists thought EH, HHV+ 1% Leaf, and HH + 1% Petiole had the
least astringency and least bitterness. When this fact is related to
the tannin content after 5 months fermentation, it can be seen that
those same samples also had the lowest tannin levels of the nine
different treatments. In aroma intensity, the panelists found no

differences between the nine treatments.

Juice Sensory Analysis:

Sensory evaluation of Concord grape juice consisted of rating the
factors of flavor strength, flavor acceptability and astringency. The
means for each of these factors, as rated by 12 panelists for each
treatment, are shown in Figures 10 - 12. It can be readily seen that
the ratings for each of the juice factors follows the basic pattern
which was seen in both the red and white wines, with the EB sample
scoring highest and the 5% Leaf plus 52 Petiole sample scoring lowest.

In between these extremes, it can be noted for each quality factor that,

generally, the panel ratings decreased as MOG increased.

54

oHuou m uaooHuHameIaoz I .m.z
Ho>oH Nm an oucmonHsmHm I

 

 

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oaou< uo>on maou<

 

 

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55

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56

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57

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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one:

58

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umooH
:—
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59

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.NH ousmHh

huaowaHuum<

 

 

 

 

 

 

 

 

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umooH

 

SUMMARY AND CONCLUSIONS

This study indicates that MOG content has a definite affect on
the chemical constituents and final quality of juice and wine. The
total phenolic, flavonoid and tannin contents of wine and juice as MOG
content in the harvested grapes increases.

The quality of white wine made from mechanically harvested Aurora
Blanc grapes was not as good as that made from hand harvested grapes and
it was felt that this was due to the 4.7% MOG content of the mechanically
harvested samples, although some of the differences could possibly have
been due to maturity differences between the samples.

The MOG content of mechanically harvested Concord grapes contained
only 2.6; MOG and many of the sensory qualities (i.e. flavor and aroma)
were heartier and more pronounced in the final products from this fruit
than those white Aurora Blanc grapes. However, it was found that MOG
also adversely affected the quality of juice and wine made from the
Concord grapes. The samples with added leaf tissue were less acceptable
than those which only contained petiole tissue. This was probably due
to the greater surface area presented by the leaf tissue, which allowed
for more leaching of the leaf constituents into the wine, so leaf tissue

seemed to have a greater effect than petiole tissue.

60

APPENDICES

61

APPENDIX I

Gallic Acid Standard Curve

=765nm

0.7
0.6

 

0.5
0.4
0.3

Absorbance

Q2

0.1

 

 

° 102030405060

Conc. mg/loo ml sample

APHflmIXII
GRAPE JUICE TASTE PANEL

Name Sample No. Date

Each characteristic increases in intensity from left to right. Rate
each of the characteristics by tasting the grape juice and then
placing an 'X' in the appropriate box.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SWEETNESS
lightly very
sweet sweet
ACIDITY
slightly very
acid acid
ASTRINGENCY (see below)
slightly very
astringent astringent
FLAVOR STRENGTH
low flavor high
strength flavor strength
FLAVOR ACCEPTABILITY
very very
acceptable unacceptable

NOTE: If you are unsure about the astringency factor you may wish to
first taste the very astringent sample which is provided.

Name

 

Each characteristic increases in intensity from left to right.

APPERDIX III

WINE IASTE PANEL

Sample No.

 

 

Rate each

characteristic by first smelling then tasting the sample and placing an
"x" in the appropriate box.

SMELL

Aroma Intensity

Aroma Acceptability

IASTE

Acidity

Astringency

Flavor Strength

Flavor Acceptability

Aftertaste

Bitterness

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

imperceptible very strong
pleasant unpleasant
slightly very
acid acid
slightly very
astringent astringent
low flavor high flavor
strength strength
very very
acceptable unacceptable
no strong
aftertaste aftertaste
slightly bitter very bitter

*Astringency (if you are unsure about the astringency factor you may wish to

first taste the very astringent sample which is provided).

LIST OF REFERENCES

CITED REFERENCES

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