100 Years of Measuring the Fat Content of Milk lonel Rosenthal and Baruch Rosen Department of Food Science, Agricultural Research Organization, The Volcani Center, P.O.Box 6, Bet Dagan 50250, Israel In the first half of the last century, nearly every farming family was supplied with milk from its own cows, and the dairy products most common on the market, such as butter and cheese, were largely household made. Fresh milk, although considered a very desirable food, because of its perishability, was consumed close to the time and place of milking, and it was an insignificant item of trade. The industrial revolution and the great increase in urban population near the middle of the 19th century led to the establishment of first cheese and butter (creamery) factories (in the United States in 1854 and in 1872, resuectively). he introduction of the power centrifugalseparator, between 1880 and 1890, resulted in a greater expansion of the butter industry (1). The creameries furnished a definite stimulus to milk production and to development of an increasing market for fluid milk. It was imperative to use some means for detecting the common adulteration by watering of milk. The lactometer, probably invented by a Frenchman, M. Quevenne early in the 19th century, was similar to an ordinary hydrometer furnished with a scale to indicate the milk specfi gravity and was among the first satisfactory devices used to detect this adulteration. First creameries operated on whole milk, but eventually the system was changed to that of also bringing to the factory only cream that was separated by gravity a t the farm. Earlier attempts to determine the correct market value of farmers' milk and cream were weighing andlor measuring the volume of milk or cream received. It was immediatelv atmar.. ent that injustice was done by paying the same price for aU milks reeardless of the butter fat value. Trading - cream was even more difficult, as the fluctuations in its fat content were much larger than in milk.
solution and comparingwith a standard table relating this parameter with fat content (in a modern version of this analytical approach; i.e., Wollny acetic acid-ether method, the refractive index of the extract is measured and related to the fat content). Alternatively, after evaporating the solvent, the volume or the weight of the residue gave the amount of fat. The weighing of the residue still is used in modern extraction methods, such as Schmidt-Werner (hydrochloric acid-ether) and Rose-Gottlieb (ammonia-ethanol-ether) gravirnetric methods.
Extraction Methods to Determine Fat Content In the laboratory it was possible to estimate accurately the fat content by extraction of fat with a solvent. Dry and wet solvent extraction methods were available (2).In dry gravimetric methods, a weighed sample was dried over an absorbent and the fat was extracted by a suitable solvent, usually ether. Thus, in the Adams method the milk sample was absorbed on a coil of filter paper which was then dried and extracted. Other absorbents used were sand or asbestos. In wet extraction methods, a measured sample of milk was treated with acid or alkali solutions. followed bv fat extraction with an immiscible solvent. he solution of fat was separated, and the quantity of fat present was estimated. For example, in the Soxhlet alkali-ether method this was done by measuring the specific gravity of the fat
Inaccurate Optical Test The lactoscope, invented during 1870's by a Professor Feser of Munich, was an inaccurate optical test that never enjoyed popularity. A simple version of this instrument was described as a "circular elass dish. on the underside of which was a fixed pattern i f black &allel lines clearly visible through the transparent material". A measured quantity of water was placed in the dish, and the milk to he examined was dropped into it and stirred until the eye could not distinguish the number of lines in the pattern below. The number of milk drops required for this distortion was then related to a table with the percentage of butter fat.
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'~iklausGerber (185&1914) was trained at the Universities of Berne, Zurich, Paris, and Munich and spent two years at the SwissAmerican Milk Co. in Little Falls, N.Y. After returning to Switzerland, in 1887. he founded his own daiw. named United Dairies of Zurich. ~ecauskof the Door aualitv of &due to lackof hvaiene and dilution with theseb;oblems bv effec..~.writer, GP& .. .. S; hisdoal - = - - to -- eliminate -~~ ,~ twely test ng tne m ik. n 1892 in the swrss Mrk Journal, G&& presents hs 'Acia-B~tyrometry', a fast,slmp e ana re1 aole analys s of fat content in milk. The test, originally meant to be used only by his own daiw, had not received extended experimental attention and did not assume its present form until 1895. ~~~~~~
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Lengthy, Inaccurate Analytical Procedures The extraction methods were too difficult and slow for use in the creamery and more expeditious analytical procedures were suggested (3, 4). In the "creamery inch" method a sample of milk (113 cubic in.) to be gauged was poured into a cylindrical vessel (creamometer or cream gauge) immediately upon being taken from the cow. After standing for about 12-24 h the height of the cream layer was measured. A "creamem inch",. i.e.,. a 1-in. laver of cream in the vessel was taken as representing one pound of butter. The method was not only lengthy but also inaccurate, because of variations in the raiesof creaming of milks of different oripins, and in the fat content in the cream luycrs obtained In the '.churn test", the cream was churned in a tin can and the butter formed was collected and weighed (allowance was not made for the fat content of the buttermilk). In the similar "oil test", the milk or cream was churned in a 9-in. long graduated glass tube, the tube with contents was then placed in a warm water bath until the butter melted. and the volume of oil formed was read on the graduated scale. The tests were subject to verv considerable errors because of the ineEciencv of the ch;rning and the narrowness of the layer of fat obtained.
Primitive Centrifugal Methods Primitive centrifugal methods also were advocated. In the "Fjord's tester" ,1878, the milk samples were whirled in ordinary test tubes in a centrifuac until the cream was compressed into a top layer containing about 70% of fat. The volume of cream was measured by means of a pair of dividers marked with graduations on an attached quadrant. In the "ladocrite" test, introduced by De Lava1 in 1885, centrifuge and acid were utilized for the first time in a direct volumetric estimation of fat. The milk (10 mL), acidified by addition of 10 mL of a mixture acetic acid:sulfuric acid (20:1), was warmed in a water bath at 80 "C, for
15 min, the acid digest was poured into a metal test bottle fitted with a elass "tubulure". and the temoerature was lowered to 6 0 k . The test bottie was then placed in a cmtrifurre head constructed to fit on the soindle of a De Laval cream separator (replacing the normal bowl) and was whirled for 5 min a t 5000-7000 rpm to separate the fat. The centrifuge was heated with hot water to keep the temperature above 50 'C. The volume of the fat was read on the graduations of the glass tubulure. Introduction of the Babcock Test In 1888 Stephen Moulton Babcock (1843-1931) came to the University of Wisconsin as a professor, and combined this position with that of chemist and later director (in 1899) of the Agricultural Experiment Station until his retirement in 1913. At that time the dairy industry was makinggreat strides in Wisconsin, and William A. Henry, Dean of the College of Agriculture, pointed out to Babcoek the great need for a practical test for fat in milk and cream. Babcock, a native of New York, graduated from Tufts College in 1866. After serving for two years (1875-1877) as instructor a t Cornell University under professor Caldwell, he studied for two years at the George Augustus University in Gottingen in Wohler's laboratory, under Hans Hiibner, obtaining his degree in 1879. Formally, he was the last American student who obtained his degree before Wohler's retirement (5).It seems that the atmosphere in Wohler's laboratory was very friendly. Babcock recalled that on one occasion, when chided for "wasting" so much time on American students, Wohler answered, "I know, I know, but they are all such nice boys" (6).Appointed chemist a t the Agricultural Experiment Station in Geneva (New York) in 1882, he remained there six years.
Announcement of the Babcock Test
The Bulletin of the University of Wisconsin Experiment Station No. 24, entitled "A New Method for the Estimation of Fat in Milk Especially Adapted to Creameries and Cheese Factories", published in July 1890, described the new Babcock test (7, 8).For the first time, the test employed a combination of fat release by sulfuric acid, and centrifugation as a means of separation the fat. The whole procedure was so simple that anyone could learn it in a short time. In milk, the fat is dispersed as an immiscible emulsion in the aqueous phase of milk plasma. The stability of fat emulsion is attributed to a-protecting membrane surrounding the nucleus of the fat globule. This encapsulating material consists of a mixture of proteins and lipoproteins
organized in an arrayed, heterogeneous arrangement. In Babcock test, concentrated sulfuric acid (17.5 mL of&SO4, sp. gr. 1.82-1.83 a t 20") is mixed with milk (18 g) in a special calibrated test bottle (Fig. 1).In these specific reaction conditions, the acid hydrolyzes the milk proteins to constituents which are no longer capable of maintaining the fat droplets in the emulsified state of dispersion, and also char the lactose; the fat is not affected (complete digestion of organic matter requires 7.3 g, 9 g and 18 g of 98% sulfuric acid for 1g of carbohydrate, protein, and fat, respectively). The heat generated by the reaction (- 101°C) melts the fat globules and contributes to coalescence and phase separation. At the temperature reached during testing the fat has a specificgravit; of 0.9 compared to approximately 1.43 for the acid mixture. The separation of fat is assisted by centrifuging the test bottles. The amount uf fat in the sample is dctcmined directlv bv measurine the heieht of the Sat column collected in t6e lalibrated k c k . ~ a c 1% c graduation has a capacity of 0.2 cm3. The specific gravity of butter fat at about 60 'C, which is the temperature at which the test is read, is 0.9 g/cm3. The 0.2 cm3 of butter fat, therefore, weighs 0.18 g. If 0.18 g fat represents 1%of the milk tested, 0.18~100gofmilkmust be used. In the case ofmilk, the sample is measured, instead ofweighed, into the test bottle. The averam specific mavitr of milk is 1.032. Hence, 18 g of milk havea volume of 17.44 cm3. But when milk is ooured from the oioet. a ~ ~ m x i m a t e0.15 l v cm3 remains in ihe pipet and faiis be discharged into the test bottle. For this reason a 17.6 mL oioet which delivers 18 rrof milk. is standard equipment fo; ihe Babcock test. Babcock's test bottle was the same shape only smaller and of heavier glass. as that used a c o u ~ l eof years before by Short (9, who used a mixture of aceti;and s;lfuricacids to obtain free. and thus insoluble fattv acids. in samoles of milk hydrolyzed by alkali. The voluAe of separatei fatty acids was estimated in the calibrated neck of the test bottle. The centrifuge has undergone considerable changes since the inception of the Babcoek test. The transition has been from unheated, hand operated, to the electrically powered and heated centrifuges. 'The earlier centrifugalizers as Babcock's . . . were heavy pieces of mechanism turned by hand . . . Where steam or electric power was ready a t hand rotation was effected by mechanical means, but a yard of strong window blind cord attached a t one end to a wooden handle, wound a few times round a pulley encircling the spindle, and withdrawn by a smart pull, precisely as in spinning a top, will cause the disc to revolve for 3-5 min, and being quite sufficient is almost everywhere preferred" (10). The electric powered centrifuge was introduced sometime between the years 1900 and 1909.
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Babcock Test Promoted Honesty
Babcock's refusal to patent the method was a factor responsible for the widespread of the test. It soon was adopted for ~ e n e r ause l in the United States, Canada, New zedand, ~u;tralia, and South Africa and has been instrumental in olacine the dairv industrv on a substantial and permanent basis. Because it made possible to pay for the true butter fat value of the milk and cream, it was said that "The Babcock test did more to promote honesty among dairymen than reading the Bible ever did" (11).Also, the test enabled the grandiose improvement of the dairy breeds of cattle by providing a handy tool for determining the butter fat production of the individual cows in a herd. Few inventions relating to agriculture have been of greater practical significance.
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Figure 1. Babmck test bottles for milk (A). cream (B), skim milk (C) and buttermilk (D), and E, plunger for checking the accuracy of cali-
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Additions and Suggestions by Others
Shortly aRer the introduction of the Babcock test, Leffman and Beam (12) suggested the addition of amyl alwhol and hydrochloric acid to the sulfuric acid as a means of assisting the fat separation and shortening the whirling time. The use of amyl alcohol was reported also by Beimling (13)and James (14). Gerber' (15) found that the addition of hydrochloric acid is quite needless, since the addition of a small amount of amyl alcohol alone, greatly facilitated the fat separation after treatment with sulfuric acid (as a matter of fact, "amyl alcohol for milk analysis" is a mixture of isomers in which isoamyl alwhol predominates). In the Gerber test there is no addition of hot water between the whirlings. Gerber also substituted the flatbottomed flasks used as test bottles by Babcock, for special stoppered glassware called lactobutyrometers (Fig. 2). Then term lactobutyrometer was first introduced by Marchand in 1854 (16) for the fust volumetric method of estimating fat in milk. The technique of Marchand's consisted of mixing, in a ladobutyrometer, 10 mL of milk, a drop sodium hydroxide, 10 mL of ether and 10 mL of alcohol. When the ether-fat layer had separated fully, the number of divisions on the graduated neck were read as degrees and converted by an empirical formula to weight of fat in grams. Babcock and Gerber Tests-Tests of Choice While the Babcock method is the test of choice in North America, the Gerber test has found wide applicationinEuropean countries. A remarkable fact is that aRer almost 100 years ofuse, the two methods are virtually the same a s when they were first introduced in 1890-1892. Several methods utilizing alkaline or detergent solutions that circumvent the need of the corrosive sulfuric acid in the ordihave been suggested' nary Babcock Or Gerber but they have not found general acceptance. Ironically, however, the 100 years anniversary of Babcock-Gerber tests may mark the depreciation in the importance of chemical tests for fat. ~-~~ Significance of Fat in the Diet Changes Today, when the value of milk is gaining prominence, the prestige of fat as a human nutrient is not what it used to be. The milk composition is routinely determined by clean, rapid and accurate, nondestructive infrared techniques (which, however, are yet to be calibrated by BabcocWGerber methods!).
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Journal of Chemical Education
Figure 2. Old-style Gerber butyrometers. ~i~~~~~~~~ cited ,,-,,, c.c.; MeKay,G. L.; hrsen, c . B
~ ~ ~ ~ N~ ; ~w ~ 1m9:p2. IY ~ : ~ ~ ~ , 2, wi.bn, A. L.; winton, K B.; ~ h ~o ~ i ~ s r ~w1ley: ~ f N~~ W ~ Yo ~ dL 1 9, ~4 5; : 725~~ 732. 3. Hunziker, 0. F TheButlerlnduafv: La Grange,IL. 1940:~ 11. 4. M ~ D O ~ ~FI H. I . ~ l ~ i~ t~ t . ~ ~ bianuol; o l l ~ N~ ~b Wzealand uniuersit7 h a s : W ~ I lington, 1953; pp 14861487.
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7. ~abeock,c ~.msc.AgrEjlp(.StoBuI. 1890, No.24. 8.Bsbeoek.C. J, lEsc.&r Erpt Slo. 7lhAnn. Rpf. 1890.98113. 9. Shorf F. G.Wise Agr E r p ~ Sia. Bul. 1888, No. 16. 10. Will~ughby.E. F Milk. ItsPmductran and U w ; C Griffin and Co.: London, 1904: p 229. H. L.Selonce 19S1, 74.8687. ll. 12. ~ e r m a n , n : ~ e a w m ,~ h t ~ m i y 1892.17,8354. st
i: gEr;,;; ~ ;zLg.$i ~ $~ ~ ~~~ ; & ;,'~~~: ~ ~ , No, ..her,N. M ~ I C ~ 1892,21,891: 1833.23.656; 1895. 25,169. 16. Marchand, E. J do P h r m . el & Chimlo l854,26,34&352.
