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THESIS

A Simple Test For Sour Milk

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A STMPLS!) THEST FOR SCUR TILA.

Ti nearly all Yorrms of doug’ rixturces a sunvlv of 10° gas is

necessary for the leavening or "raising" of the mass, This is obtained
in various wavs, but the ordinary housekecrer is limited to the use of
yeast, paking powder, or soda, and for the rrenaration of manv artislcs
of food the last two only are nracticable, Reking nowder, wher rur
a neutral misture of c:ram of tartar, soda, and starch, containing
about twelve vorcent of T05 SAS, wnien iss liberated by simpliv dissolv-
ing the vowder in the hatter, dowh, or whatever it mav be. Sinre bake
‘ing powdey id cof itself a -.ecutrel substance, i.e., neither acid nor
alkali, it cannot be combined with an acid one, e.g. sour milk, if the
resulting comnound is to be neutral, put i* mist be used in combination
with water or sweot milk. The action of soda (sodium bicarbonate,
"RHCOs) is very difforert, It is an alkaline srt, cortaining over S8if-
ty two percent of COe, whieh is liberated by the following chemical
~yosess: Sour milk contains a varving rrorortion of lactic acid, ana
Siw lactic acid unites with the picarnornate to Porm sodium lactate,
"%% gas being liberated at tec sare time,
Ir. comparing the use of soda and sour milk with the use of

“eninge vowder there are two poirts in favor of the Bormer, In the first
Lace iit is more economical, in that it disposes of a quartity of
atovial which would be useless for other purposes. Secondly, the
-“onunt of chemicals remaining in the mixture is mich less with soda

$'.an with baking powder. It has been stated that pure baking powder

contains only twelve peree:+ of carbon dioxide, while soda cortains
Pitty twer peo: A Jo: 3 teaspoornfil of soda containgd 2.2 grams of
THESIS

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602, while a rounding teaspoonful of baking powder cortains only .696
yrams, Ono ever. teaspoonful of soda is sufficient for one pint of sour
glik, tut to nroduce an equal amount of COs it would be neecssarv to
ige three rounding teasroorsful of baking powder, or six times the bulk
to the game amount of liquid, It is easy ta see from this that the
touble tartratc of potassium ana sodium (Rochelle salts) wnich is left
i
sehind from the baking rowder mist. be cresernt in mich larrer quantity
har the sodiim lactate whieh is formed in the other cage, The same
thing is tmio ina greater dersree when the oquivalet of baking powder
t.e, soda and cream of tartar, is empioycd. This chemical mixture known
'& Rochelle salts is used in medicine for its cathartic nrovertied, and
4---the question has recently beer. raised as to the nealthfuiness of
speumixe so mon or it in baking powder mixtures, Whether its effect
Arjurious or rot, the ~resence of SUCH a quantity of foreign sub-
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mynee is certainly not an aavr: tage,
Bit while the us of sour milk and sode is rreferable in the
ST 4s roted, it has also a disadvantage, The housekcerer finds, for
ex: “yle, that it is a very easv matter to make muscuits"according * -
“ y" and a very difficult one not to have them yellow ard unapneti--
a, “re trouble lies in the fact that an excess of soda has been used,
 .pose, as before explained, is to neutralize the lactic acid and
* + 3 the mixture light by the consequent liberation of COs, If more
>: ° present than is sufficient to accomplish this purpose, the heat

-~- ?" ; gven causes the amount remaining to undergo a chemical change,

—360me sodium ‘morocarhonate (salr da, NapC0,) with a furtcer

TT a den OF Tal Mts. 7 eda 4 +: 6s the yellow color, bee ing

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greenish if a verv larze excess hes recn added, owing to ignorance of
fhe exact amount of acid vresernt in the milk, This arount varies in
Milk ordinarily used for cooking, from one fourth to threc fourths of
Me vercent, ikich higher than this it cannot Fo, ovine to the death of -
‘he germ whieh produces the acid, Nence if the strehgbh of the acid
2resert is not known it is imvossible to use exastiv the correspondine
amount of alkali. The object of the cxreriments undertaker in this
thesis was to devise sone conramafively sirrie means, whieh should be
available to the ordinarv cook, for determining the derree of acidity
in sour milk, thus enabling her to use the correct amount of soda to
neutralize this acid,without using an excess,
Sinee the idea was, in some resrects, an original one, it was
scessaryv to have a working foundation, haser wunon some hvzothesis, It
5 assumed that, if a niece of porous paper, suen as plotting paper or
Ater paper, were dinred in an alkaline solution of Known strength,
‘lowed to dry, then dinved in an acid solution of correspornaing
*ferngth, the alkali orn the surface would be exactly reutralizes bv the
td with which it came in contact, A scerics of exrerimerts were
‘pried or, based unon this assumption,
Sodium carbonate, NanC0e, was tne alkali selected, bedause of
123% solubility in water, and permanence upon exposure to air. .5888
~vrams of this dissolved in one hundred cubic centimeters of water gives
x aotution gmhose strength is just sufficiert to neutralize a one per-
sent solution of lactic acid. For three fourths, one half, and one

“yMurth vercer.t .olutions take ‘he corresponding fraction of .5888, In

ree AER aang 000 (UF rnarernt, should the acid hr ny
rea
effect, it became necessary to color the paner with ar indicetor before
Minring it into the alkaline solution, Cochiveal an“ methyl orange were
Sried, rut with unsetisfactory results. Litmis, hovever, proved to be
mich more sonsitite.

A blotting varvar of excentiourally loose texture vas first
@xperimentcd with, Strives of this, coior.d ivy litims, were dirred into
sodium carbonate solutio:s of varvirnes strength, dried, and dirred into
acid solutions of corresponding strencth., It was found, nowever, that
the weakest acid solution produecc the echanre in the stronzest and
weakest ray rs alike, This was dounbtiess due to tre fact that, on
account of the loose texture of thie naver, the alxali was immediately
diffused through the lidnnuig, ana the raver lost its strength, A thieckor
*ort with a firmer texbure was next tries, put wit no more setisfact-
Yry results, for, because of the corvast nature of the raner, the alk-
cli was not distributed evonly, ana the acia affeecte some snots, while
*hers remained unchanecd, Ordinary thin filtcr rnare~ ves frec Crom

weher of the foregoing difficulties, mit tne texture vas umoven, heing
“.ieker in some places tnan in others, henee it also ves unavailable,

Since the use of test travers ha’ vroven a failure for the
- =fLous reasons described, it was necessary to cast about for some
“Sar medium which should combine firmness ard evenness of texture with

of eloth
“himness., A fine, firm quality, was selected as possessing these req-
attes, and the previous exper’wnents were repeated with far more grate

“ring results, It was found t at the distinction between the one

surth ana one half pereent sc itions of lactic acid, and bets cer. °

aware Bey 0 be c‘early showr., Other test = —-:
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made, using me. inste ta of epotie acis so’utions, and the results were
verified tv Sitration with standard alkali, the ordinarv laboratorv
mears for setermination of enridaitv,

Tronmeaking toads test a7 is neeessarv +o ovserve several rre-
Gautions. In the first plnaes, tho cloth strins mist rot be allowed to
renain in the milk more tu6™ an instant, otheormvise there will be daif-
fusior. of the alkali, with consequent weakening of the strength of tho
testing strin. For the same reeson the surnius liquid on the surface
@hould te immeciately remove. ip wirine the cloth with a niece of

filter parecy, or sometnins similar, Thirciv, the correct result is rot

fully aprarert until the expiration of several minutes, The acid, no

. matter how weak, mav change the color of tise surfece immediately, but
y
et the erd of five minutes the acid and alkali will nave come in con-

¢act throughout the strip, If the eloth now nas a decided red color the
ecidity of the milk has at least a vereent corresnonding to the amount
of alkali on the cloth. If it is still hlue, however, trv one having
the next lower percent of alkali. There wilh sometimes he a fer red
s-ots on tue surface of the cloth, owing to the fast tnat not ell of
t'e surplus liquid was removed, hut theses should be disregarded,
This test was fried rereatedly or. different samples of milk
“4#n verv satisfactory results, considering the necessarily crude nate
of the exvorinerts, No sample tested more than three fourths per-
=, and the majority of those taken from milk desigred for cooking
viynoses hac an acidity of not over one half percent. This proves that,

““atle the rule -f " a jJ-vel teaspoorful of soda to a pint of mi)’."* is

‘art oor er | oor Yr wif’ -“s maximim acidity, that amourt
a
ordinarily bo too great. Tro thirds of a teasnoorsni. is suffieier.t for
@ pint of milk at one half norecert, ana one third of a teasnoorfMmi wnen
the acidity is one fourth rerrert, The test is one whnien is verv easily

vplied, and even the mamniactuse of the testins strins by tre ordinary

mersor. is not irnmossible, A Nurther exvlanrtion of this last point

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wouls rernan:

Tne atonis of softtium earhonate is 106, that of lactic
acid is 0, auc since sodium carbonate is a divalent, and lactic acid a
ménovalernt, comrouni, 39 gsrams of Jactia aecit will neutralize nalf of
106 grams of sodium carbonate, or 52 grams, A one veoreert solution of
lactic acid is practically one which contains one gram of lantict acie
to 100 cubic continet rs af water, and to neutralize this it is necess-
ary to have a solution of sofaium eernonate containing 52 / 90, or 58%
‘rams to 100 cubic centimeters of wete», In the ordinam svsterm of
vaignts and measures this is equivalent to .7F52 ounces to a gallon of
water for the three fourths rereent solution, or .482° ounces for the
one half pnercert soluticn, The soainm carhovete (salsodae ) as ordinarily
o“tained 33 not drv, but will beeome so by leavins in a warm place for
e-veral dava. Any Firm cloth of a fine quality will answer, Dry litme
-vy be obtained at a dmg store, which should be crushed ard dissolved
water until a strong enough solution is oitained to make the cloth a
sided blue. Dip the cloth first in the li’ «1s solutior, dry it, then
Ir. the solution of sodium cerbonate, han: up and drv, It is then

lv to cut up for use after a striv around he edge has beer. removed,

y. ‘ ar acxeecses of the earbonate is likely t) Pe liected,

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