THESIS .

Perpetuationl of M iik Siaz‘vtérs ,

J. A. Du'nrord ‘ 13,-). Dan
1902 '

 

 

 

 

 

 

THESIS

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T H E S I S

H P E T U A T I O N

L K S T A R T E R S.

. "B'éy
J"; A; DUNFORD

a n d
7

E R N E S T I. D A I L

Michigan Agricultural College.

1 9 O 2.

THESIS

PERPETUATION 0F MILK STARTERS.

In the modern dairy, creamery, or cheese factory of

at
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'18

2-4 .

to-day, a starter for securing the desired ripeness c
nilk or cream has become an indispensible factor in making
the Test and most uniform quality of either butter or cheese.
By the addition of a starter the ripening process is not only
hastened, out in many cases the undesirable bacteria already
in the vat are held in check by the predominance of the
starter added.

The dairyman secures these starters in various ways,-
some take buttermilk or skimmed milk, and set it aside
under suitable temperature until it has hecoue sour, thereby
developing the germs in the milk. In this method it very
often happens that the milk or buttermilk used as a starter
contains undesirable germs. thich are not held in check and
multiply with the desirable ones, until when introduced inn)
the vat, tLey very materially deteriorate the quality or
flavor of the butter or cheese. Another way to secure a
starter is to obtain a small amount of whole milk in the
cleanest posmible condition and put in a CTCé‘tn place 130 sour.
While this is a better method than the first described ami
even though the milk is secured under the cleanliest condi~
tions, yet there are many chances for undesirable germs to
get into the milk and there increase from day to day until
ultinately they seriously affect the final product. Still

another, and the most conron and best ray of securing a starter,

sso41

is by purchasing a bottle of comrercial starter a ich contains
the ‘acteria in a concentrated form and when a dad to milk it
gives a very strong and vigorous ripener. The contents of

one of these bottles are emptied into a can of pasteurized
milk, and this allowed to sour. A portion of this is then
taken out as a starter for a new can of milk, the remainder
being put into the vat. This process is continued until the
starter, not being kept pure, becomes too weak for further
use, which is usually about two weeks, when a new bottle must
he purchased. While this is a very effectual rethod of se~
curing a starter, yet there are Many faults even to this method,
among which are the following:

1. It necessitates buying a new hottle of starter
every two weeks, which is an inconvenience not alone because
of the cost, hut since the starter will k ep only a very
short time,it must be purlhased by single bottles from the
manufacturer.

2. Oftentimes the bottle of starter becomes contami-
nated, and this contamination may cause trouble in milk or
cream.

3. The dairymen seldom pasteurize their milk sufficient-
ly to kill all the undesirable germs in the milk used as a
starter.

4. The room temperature varies so from day to day
that there is no uniformity of the starter as it goes into

the vat, and hence no uniformity of the final product.

The object of our thesis was to devise or discover, if
possible, some method by Which the objections to the
starterxnow in use would be obviated or at least decreased;
in other words, to discover some method by which we could
secure a starter consisting only of the desired bacteria,
and free from undesirable ones, and one sh ch would retain

and
its vigor,nnot in the least become attenuated, and thus do
away with the expense of securirg a new starter frequently.
Such a process must necessarily fulfill seven essential re-
uuirements to make it successful. First. There must be

a pure culture of the desired bacteria to start xi,h, for if

more than one species were present one might soon supplant

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the ct1,rs. Second. To overcome the difficulty of using

.—

milk as a mediunwhich is not thoroughly sterilized, some

means must be afforded by which re could secure sterilized milk.
Third. There must be an abundant supply of oxygen to

promote the growth of the bacteria in the starter. Fourth.
There must be a total exclusion of foreign germs, for if germs
from the air were allowed to get into the starter it would

soon become contaminated with undesirable germs and the de-
sired bacteria rould lose their supremacy. Fifth. A uniform
temperature must be maintained, so that a certain strength

.-

of starter can be depended upon for a certain amount of milk
offthezstarter

used and a certain time of development. Sixth. The acidity)

at which the sterilized milk is introduced must be SO regulated
as to secure the most vigorous growth of the germs. Seventh.

An effectual Means must be secured f,drawin§ off the ripened
starter, from the vessel in which i 18 gTOW .

The first of these coz'zd:i.tiol«.s, that of securing a
pure culture, was perhaps the easiest to fulfill, the

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tic acid germ of milk being very good for tle ripening of
cream or milk and giving a good flavor to the product. It
grows well in a medium of milk under ordinary temperatures
and conditions, so all that was needed to secure a pure
culture was to isolate a vigorous lactic acid germ.

In securing each day a quantity of sterilized milk
to be used as a medium we conceived that hy a series of three
cans so arranged that the milk could be heated in the first
and then drawn off into the second can and heated there
the second day, and, finally, drawn into the third and heated
there the third time, that if such a process as this were
secured, we could by introducing a certain quantity of
milk into the first can each day be able to draw off from
the third can the sane amount of sterilised milk. Our main
difficulty here was to secure a means by which the milk could
be carried from one can to the other. At first we thought
a series of syphons would do this, but on exterimenting we
found that because the specific gravity of the contents
oi the three cans were the same,the milk from one would dif-
fuse throughout the other two. Later we concluded that if
the cans were placed one above the other and connected with
tubes closing by a "stop valve," that the milk could be run
from one can to the other without mixing. The same arrangement

would afford a means of conveying sterilized milk from the

 

 

cans to the vessel containing the starter. To supyly plenty
of sterile oxygen we conceived that since gwris would not
pass through cotton wool plugs or asbestos, openings could
he made at the top of the starter can a;d these openings
filled with cotton wool or ashestos. To exclude all foreign
germs would mean that all covers and openings to both the
cans in which the milk was sterilized and the vessel in which
the pure culture was grown must be made with tightly fitting
screw confections. The cheapest method of maintaining a
practical uniform temgerature for the starter can
was to pad it with asbestos and leave a dead air space between
the padded walls. One or the greatest difficulties in plan-
ning the entire device was to secure a valve simple enozgh
to draw off the ripened starter and at the same time keep
foreign germs out of the opening. After examining the con—
struction of several different kinds of valves, we decided
that a large "out off" valve would accomplish this. For
diagram of the entire device see page 10 with index to the
same on page 11.

After this diagram had been made it was found that to
make the device durable and perfect it must he wade of tinned
copper. Neither the tine alloted to do the work or the finan-
cial means would allow us to construct the machine for our
thesis work, so that to find out as far as possible the prac-
ticability of the device we had planned,we resolved to test

it with a cheaper device. We had a tinsmith make for us a

set mf cans as on page 13. By the use of these cans and the

steam sterilizer in the Bacteriological Laboratory W9 WGTG
able to secure each day sterilized rilk. For a starter
c an we were able to use a one and one-half leiter flask
into which was put the pure culture lactic acid germ, to which
was added, by means of a rubber connection, the sterilized
milk from the cans. The ripened starter was drawn off by
means of a glaes Syphon. Oxygen was supplied by allowing
the air to pass through the cotton plugs. This apparatus
was a very crude way of testing the device which we had
plz'inned. , for there were many things which we could not
Control, sueh as the temperature of the starter and contamina—
tion with foreign germs,because of the crude connections used.
ictwithstanding these difficulties,we succeeded in carrying
on a pure culture for seventeen days without contamination,
during which time we secured the following results, using
each day 1000 0.0. of sterilized milk as a medium.
1. Time required for heating to fully sterilize.1000 c.c.
of milk was thirty minutes each day for three successive days.
2. The acidity of the milk was apparently not changed
by sterilization. The acidity varying from 15 to 25 degrees.
It was found that if the acidity got above “5 degrees the milk
would curdle upon heating.

5

5. We found that the amount oi starter to he used to
secure the desired thickness necessary for a first class
starter depended entirely upon the temperature of U18

surrou ding room. We found that when 20 c.c. of the culture

was used and subjected to a temperature of 35 degreees C.

that it required only about fifteen hours for it to sour.

0n the other hand, if only 15 c.c. were used under a tems
parature of‘lO degrees C.it required 48 hours for it to sour.
Since it is most convenient for the dairymen to so develop

his starter as to have it for use every 24 hours, we endeavor»
ed to establish as accurately as our crude apparatus would
permit, a table stating the different amounts to be used

for he different temperaures, so that each would have the

proper development in 24 hours.

Table is as follows:

Amount of Milk Used. Temperature. Anunuu38tarter Used.

1000 c.c. 12 C. 40 c.c.
” ' l4 " 35 "
” ” 15 ” 32 '
" ' 16 ' 30 "
" " 17 ” 25 ”
n I! 18” 21!!
” ' 19 ” 18 '
" " 20 ” 15 ”
” ” 21 ' 12 ”
1' 1' 22' lo”
a n 23 n 8 u
a n 25 n 5 u

As it was impossible for us to completely control the
temperature of the room, this is rather an approxinate table,

but it is accurate enough to prove that a direct relation

should exist between the amount of starter to be used and the
temperature.of the starter can.

4. We found that there was no trouble in the milk clog-

ging because of the heating process, and also none in the

ripening of the starter if it were drawn czf at the time
it had reached the stage of a first class starter, but if
allowed to curdle or precipitate then there was considerable
clogging.

5. It was found that we got the most vigorous growth
of the gerrs when the sterilized milk was put into a starter

of about 50 degrees acidity.

The conclusions of this thesis are as follows:-

From the work done with our temporary device we felt con—
fident that the machine we had planned, if sell made, would
provide a starter which would be much better than the starters
now used and at less cost and inconvenience than is necessary

in securing the inferior starters now in use.

_ 9 _

External appearance of the designed apparatus.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

-10-

'Diagram of the designed apparatus. -

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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-414.

 

_11_

Explanations and Specifications fot the Apparatus.

A9 a matter of convenience, the four departments through
which the milk passes are lettered 'A',"B:"C,' and ”D" in
the diagram on page 10. Departments “A“, 'B', and ”C" are
the three cans through which the milk passes during the
process of sterilization and are enclosed in a steam sterilizer
represented by red lines. Department ”D”, below the
sterilizer, is the starter can and is enclosed by a chest,
also represented in the diagram by red lines. Each separate
department has a vent in the cover, ('D" having two), in
which a cotton wool plug is to be placed to allow air cir—
culation but exclude germs. The cover of can ”8' is firmly
attached to the bottom of can "A” by means of two braces and
the connecting flue, and the cover of can '0' is connected
to can "B" in the same manner. The cover of can "D' is
detachable from.the botuam of can "C' by means of a screw
coupling. This is to facilitate taking the apparatus apart
when cleaning is necessary. All covers of the four'depart—
ments screw on tightly. The double-walled chest enclosing
can "D' is to be packed with asbestos to prevent as far as
possible any fluctuation in temperature. The sterilizing cans,
ventilators, plug valves and flues connecting the four
departments are round a feature not shown in the diagram
on page 10, but fairly represented in out on page 9.

The measurements for departments '3' and 'c' are not

given. .hey are the same as those given for department "A.”

_. 12...

The steam.enters near the bottom of the sterilizing
jacket, passes up through a perforated partition, and comes
in contact with the departments "A", ”B", and 'C'. The con—
densed steam is carried off through a small vent as represent-
ed in the diragram. The whole apparatus should be made

of brass or copper, or a combination of both.

-15..

Diagram of the apparatus used.

Departments 'A", ”B'", "C'" and 'D'" correspond to
departments "A", 'B', ”C" and ”D" on page 10.

The flues connecting the departments are rubber, constrict—
ed sith special clamps, to take the place of the plug valves
in the ideal apparatus. Department 'D" is a common 1 Q

leiter flask fitted with rubber cork and glass flues.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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