Gerber Test for Fat in Raw Milk Procedure

Gerber Test for Fat % in Raw Milk Procedure 1. Add 10 ml of Gerber sulfuric acid : ( specific gravity 1. 823) at 15 -21 c into Gerber Butyrometer. 2. Add 1 ml of isoamyl alcohol and insert the lock stopper grasp the test bottle at the graduated column and shake it until the curd is completely digested. 3. Adjust temperature of the milk sample to 22 -21 C°. 4. Transfer 11 ml well mixed milk sample to Gerber test bottle. 5. Place them in a Gerber centrifuge close the cover and lock. After the required speed 1500 rpm centrifuge for 5 mint stop the centrifuge. 6. Directly read the fat in Gerber butyrometer and describe result in fat%.

Principle or mechanism of test Both the milk and Gerber sulfuric acid • are mixed to produce an exothermic reaction that disintegrates the emulsion structure in milk (i. e. the acid produces necessary heat to complete digestion of the non fatty materials) The exothermic reaction in combination of • the isoamyl alcohol releases the liquefied fat for measurement and prevents charred milk fat. The free fat is collected in the graduated portion of the neck of the Gerber. bottle

Table (1) the minimum Fat% in different animal species. Animal species Cows Buffalo Sheep Goat fat% in milk minimum %3 %5 %4 % 2. 5

Purpose of Gerber test (Causes of decrease fat %) he milk * extract or remove the fat from the milk • k) *The agitation is not perfect * The milking did not include the last drop • which contains the last drop of fat. 2 - Calculate the total solid and total not • fatty material and protein by having the fat% and using some equations

Direct Oven Drying Method for Determination of Total Solids Content of Milk • • Determination Weighing dish preparation. Number the clean weighing dishes and dry for at least 2 hours in a forced air oven at 100+1 degrees Celsius. Store dishes in dessicator until needed (must be used within one week or redried). Touch predried dishes only with clean, dry tongs. Sample preparation. Prepare by tempering milk to 38+1 o. C and mixing. Sample and weigh milk at 38+1 o. C. Total solids determination. Remove metal shelf from oven and place next to balance. Record all weights to four decimal places. Weigh a predried sample dish. Pipet approximately 3 g of 38+1 o. C milk (nearest 0. 1 mg) directly into a preweighed sample dish. Do not chase the drift. Record the sample weight immediately after the weight stabilizes and just before it starts its steady drift to lower numbers. Remove dish from balance and place dish on oven shelf for transport to oven. Check balance zeros between samples. Blanks. Weigh 2 empty, predried dishes. Drying. Preheat the oven to 100+1 o. C. The hot air exhaust vent should be open to allow moisture to be removed from the oven. After weighing is completed, turn off the oven and place shelf plus all dishes (including blanks) into the oven, close the door, turn on the oven, and dry for 4 hours at 100+1 o. C. Do not open the oven door or place anything else into the oven until the 4 -hour drying is completed. Cooling. Remove dishes from the oven and cool to room temperature in desiccator (>30 minutes). Weigh the dish plus dry milk on the same balance as was used for the initial weighings.

Calculation • [(weight of dish + dry milk) - (wt of dish)] • • - (mean blank) Percent TS = ------------------------------ x 100 [(wt of dish + milk) - (wt of dish)] Maximum recommended difference between duplicates 0. 05% total solids Sr = 0. 019 SR = 0. 042 RSDr = 0. 149% RSDR = 0. 327% R value = 0. 054 R value = 0. 118

(Direct Oven - Ether Extraction) Method for Solids-Not-Fat in Milk • Principle Solids-not-fat is determined by conducting total solids and fat analyses. Percent fat is subtracted from percent total solids to obtain percent solids-not-fat. • Determination • Conduct total solids analysis of milk by the direct forced air oven drying method. • Conduct fat analysis of milk by Gerber method. • Calculation Percent solids-not-fat = Percent total solids - Percent fat • Maximum recommended difference between duplicates 0. 06% total solids • Sr = 0. 019 SR = 0. 041 • RSDr = 0. 218% RSDR = 0. 466% • r value = 0. 055 R value = 0. 117

Reference • J. L Clark, et al. , 1989. Journal of Association of Official Analytical Chemists, 72: 712 -718.