NOT-.,
1913
T H E JOL’RLTTAL O F I,I’DCSTRIAL
were pasteurized. This is, no d o u b t , below t h e t r u e figure on account of t h e fact t h a t t h e samples are t a k e n uniformly from t h e different dealers a n d not in proportion t o t h e size of their routes; t h e dealers selling t h e most milk are without d o u b t those who sell t h e pasteurized milk, while t h e m a n with t h e small route generally sells raw milk. T h e number of adulterated samples are about t h e same as found i n past years. T h e laboratory records would indicate t h a t there is more watering done b y t h e producer a n d more skimming is practiced b y t h e small retailer. T h e adulteration of milk is not as a rule carried on b y t h e same men. We make b u t few complaints in court alleging a second offense, for after one prosecution t h e convicted person either ceases t h e adulteration, or else goes out of t h e business. T h e actual market conditions are better in this respect t h a n our figures show because we collect such a large n u m b e r of samples from suspected persons. KO d o u b t less t h a n 2 per cent of our milk supply is subject t o adulteration. T h e alcohol precipitation test showed t h a t j.2 per cent of t h e total samples a n d 4.1 per cent of t h e pasteurized samples were sufficiently old when t h e y reached t h e laboratory t o curdle on boiling. T h e results of t h e 11.reductase test showed t h a t 5.6 per cent of t h e samples collected during seven months were t o o old t o use as food when t h e y reached t h e laboratory. If these samples could have been tested a t t h e time of taking, t h e figures would have been lower during t h e summer months b u t not much difference could have been expected during cold weather. T h e pasteurized samples were better in this respect t h a n t h e raw samples. These figures are higher t h a n would be consistent with a thoroughly hygienic milk supply for if 94 per cent of t h e samples reached t h e laboratory in good condition t h e other 6 per cent collected a t t h e same time n-ould have done so if fresh. An example of very old milk was shown in t h e samples furnished t o a cont r a c t o r , which were nearly sour when t h e y reached t h e laboratory, about t w o hours after being delivered b y t h e producer. It is fortunate t h a t these conditions are unusual or i t would be impossible for t h e consumers in congested districts t o obtain a n y sweet milk. S U M MIA R Y I . It is possible t o detect commercial pasteurized milk b y t h e Schardinger reaction b u t not b y t h e peroxidase reaction. 2. T h e a m o u n t of pasteurized milk on t h e market is greatest in t h e large districts. 3. T h e airerage quality of t h e milk is considerably above t h e legal standard. 4. The average quality of t h e pasteurized milk is very slightly below t h a t of t h e r a w milk b u t this does not appear t o be due t o adulteration. j. Pasteurized milk shows less fluctuation in composition t h a n raw milk, a n d t h e percentage of samples below s t a n d a r d is less of t h e former. 6. Fresh milk will not coagulate with a n equal volume of 68 per cent alcohol. ;. Sinety-four per cent of t h e samples delivered
AA‘D E,VGINEERIXG C H E M I S T R Y
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a t t h e laboratory gave reactions for fresh milk; t h e balance was too old for use as fresh milk. I wish t o acknowledge m y indebtedness t o m y assistant hfr. Lewis I. Nurenberg for collaboration in t h e experimental a n d routine work, a n d t o N r . Henry N. Jones for making t h e bacterial counts. LABORATORY OF FOOD A K D DRUGIKSPECTION >rASS S T t T E BOARD O F HE.4LTH BOSTON
THE DETECTION OF GELATIN IN SOUR CREAM By ARMIXS E I D E N ~ E R G
Received August 4, 1913
T h e usual method fo? t h e detection of gelatin in food products such as milk or cream a n d t h a t adopted provisionally by t h e United States Department of Agriculture’ consists in t h e removal of t h e proteids with acid mercuric nitrate a n d t h e precipitation of t h e gelatin in t h e filtrate with picric acid. I t , however, has been frequently noticed t h a t a sweet cream IThich gave no precipitate with picric acid would, after souring, show quite a perceptible turbidity on i t s addition, often heavy enough t o lead t o t h e assumption t h a t gelatin was present. I t seems most probable t h a t this is due t o protein decomposition products not precipitated by t h e acid mercuric nitrate. G. E . Patrick, in a n address on “ T h e Detection of Thickeners in Ice Cream.* made before t h e 24th Annual Convention of Official Xgricultural Chemists, speaks of what is probably t h e same or a very similar decomposition product, often found in ice cream after i t has soured. H e is not certain as t o t h e exact nature of this substance, b u t believes i t t o be d u e t o t h e action of bacteria. H e finds t h a t this “pseudo-gelatin,” as he calls it, forms a precipit a t e with picric acid similar t o t h a t formed b y gelatin under t h e same conditions a n d mentions t h a t there is no method known for distinguishing t h e one from t h e other. His suggestion, t h a t formaldehyde be added in t h e laboratory t o prevent t h e bacterial action which produces this decomposition product, is of course n o t applicable t o creams received sour. T h e picric acid precipitate from t h e sour cream is flocculent, resembling Al(OH)3 in form a n d settles quite rapidly, while t h a t due t o gelatin is small a n d granular, much like B a s 0 4 in form, settles very slowly a n d on shaking t h e test t u b e thoroughly will coalesce in large lumps leaving t h e solution almost clear. While these differences are quite \veil defined, t h e large n u m ber of sour cream samples received in this laboratory made a method leaving less room for d o u b t , in t h e detection of even small amounts of gelatin, very desirable. After some experimenting I found t h a t there was a sharply defined difference between t h e solubilities of t h e t w o precipitates in hot, neutral water. While both precipitates are soluble on heating in slightly acid solutions, only t h e gelatin picrate is soluble in hot, neutral water alone. T h e picric acid precipitate from t h e sour cream is seemingly entirely insoluble i n hot water, after all t h e picric or other acid has been removed. T o I O cc. of t h e cream are added a n equal volume 1 2
U. S DPpt Agr , Bull. 107 (re\ 1, U S Dept. A g r , Bull 116, p 24.
p 121.
928
T H E JOC’RXrlL O F I > V D C S T R I A L A N D ENGI.VEERIIVG C H E M I S T R Y
of acid mercuric nitrate, t h e mixture shaken. 2 0 cc of water added, again shaken a n d filtered after j minutes. T o t h e filtrate a n equal volume of picric acid is added when if gelatin or t h e soluble decomposition products from t h e sour cream are present, a precipitate is formed. This is t h e method mentioned in Bulletin 107 of t h e U. S. D e p t . of Agriculture. I n order, definitely, t o determine t h e nature of this precipitate, proceed as follows: Cork test t u b e which should be a large one, a n d shake very thoroughly. I n this way t h e gelatin picrate will coalesce a n d filtration be much more rapid. If possible allow- t o s t a n d for some time after shaking; most of t h e liquid can t h e n be siphoned off. T h e precipitate after being brought on t o t h e filter is washed with water containing t w o t o three drops of ammonium hydroxide t o I O O cc. until t h e washings are slightly alkaline t o litmus, a n d then with neutral water until t h e washings are neutral t o litmus. This will remove all excess of picric acid. T h e precipitate is t h e n transferred t o a small beaker and I O t o 2 0 cc. distilled water added a n d heated t o boiling. If t h e precipitate is very small i n a m o u n t i t need n o t be t a k e n from t h e filter paper, b u t both can be boiled together. Filter hot i n t o a test t u b e . T h e filtrate will contain t h e gelatin picrate b u t n o t t h e precipitate derived from t h e proteids in t h e SOUT cream. Cool this filtrate a n d a d d a n equal volume of picric acid, when, if gelatin was present in t h e original cream, a decided precipitate will b e formed. W h e n large amounts of gelatin are present t h e solution m a y become t u r b i d on merely cooling. I n order t o determine t h e delicacy of this method, 2 5 cc. of a I per cent solution of gelatin containing 0 . 2 j g r a m of gelatin were added t o j o grams of sour cream. T h e sour cream t h u s contained only 0 . j per cent of gelatin, which h a d little thickening effect on i t . By using 2 0 t o z j cc. of this cream instead of I O cc. as above t h e presence of t h e gelatin could be determined with certainty. T h e above method has been in use in this laboratory for some time a n d has been found t o work satisfactorily, provided t h e conditions described are obtained. Even smaller quantities of gelatin t h a n this can. of course. be detected b y using a larger a m o u n t of t h e original sample.
1’01.
j, S o . I I
of a given cider vinegar could be determined, a n d only t h e most obvious adulterations or substitutions could be detected with certainty. -4pparently authentic cider vinegars were reported as containing a m o u n t s of solids varying f r o m 1.18 t o 8.00 per cent of ash from 0 . 1 9 t o 0 . j 7 per cent with t h e other constituents i n t h e same general proportions. A review of t h e extensive d a t a on fermented ciders, however, showed no such wide variations in composition, a n d plainly indicated t h a t this marked difference in the composition of cider vinegars was due not t o a similar difference in t h e composition of t h e r a w material, b u t rather t o t h e method of manufacture. -4s a new a n d scientifically controlled process of manufacture h a d become widely established, a n d was t h e source of practically all of t h e “commercial” cider vinegar on t h e market, i t seemed probable t h a t t h e product prepared b y this process might differ perceptibly f r o m t h e “barrel” vinegars, a n d this s t u d y was projected with this idea in view. T h e essential differences between t h e barrel method a n d t h e generator method of making cider vinegar will be apparent from a brief description of these processes. T h e conversion of apple juice into vinegar i n t h e barrel was, until recent times, t h e generally accepted method in this country. Although no longer used for t h e preparation of cider vinegar inlarge a m o u n t s on a commercial scale, i t is still very largely employed on t h e f a r m as t h e source of t h e family supply. T h e general procedure is as follows: T h e juice expressed from t h e apples is allowed t o ferment in a barrel, usually of 40 t o jo gallons capacity, until practically all of t h e sugar has been changed into alcohol, a n d t h e resulting hard cider stored in some dark place, frequently a cellar, where t h e formation of acetic acid takes place gradually. Under t h e most favorable conditions t h e conversion into vinegar is slow. T h e long period of storage required gives opportunity for infection b y harmful organisms, with t h e development of mal-fermentations, which frequently change t h e character a n d composition of t h e product t o a marked degree. The conditions of storage, temperature, cleanliness of t h e barrel a n d surroundings are factors entering largely into t h e quality of t h e finished vinegar. T h e simplicity of t h e method as regards mechanical CHEMICAL LABORATORY features is more t h a n offset by t h e disadvantages of DEPARTMEXT OF HEALTH a n uncontrolled acetification. NET’.‘ Y @ R K CITY The rapid or generator process is carried on in this A STUDY OF THE COMPOSITION OF CIDER VINEGARS country in a 1-ery uniform practice which m a y be outlined as follows: Large quantities of apples are MADE BY THE GENERATOR PROCESS pressed a n d t h e juice collected in t a n k s , holding from B y I,. M. TOLMAX A N D E. H. GOODXOW Received August 18. 1913 zoo t o 1.000barrels where i t is allowed t o ferment until When a n investigation of t h e composition of cider t h e sugar is almost completely remol-ed. I t is obvious vinegar was undertaken b y t h e Bureau of Chemistry t h a t this alcoholic fermentation on a large scale in a b o u t four years ago, a s t u d y of t h e literature on t h e contrast t o t h e fermentation on a small scale in t h e subject showed t h a t t h e existing d a t a were composed barrel, tends t o produce a uniform product. T h e almost exclusively of analyses of vinegars macle b y hard cider t h u s obtained is run over t h e generators, t h e old barrel process. T h e authenticity of t h e t w o which consist of upright cyllndrical t a n k s filled w t h or three samples of generator vinegars reported was beech shavings, corn-cobs, r a t t a n , or some similar not beyond question because of t h e extreme difficulty porous material saturated with strong vinegar. The of obtaining t r u e samples of such vinegar. There alcohol is conxrerted almost immediately into acetic was practically no analytical basis on which t h e purity acid. T h e entire process is under exact control. a n d
