Gerber Test for Fat % Gerber Test for Fat % in Raw Milkin Raw Milk

ProcedureProcedure

11 . .Add 10 ml of Gerber sulfuric acid :( specific Add 10 ml of Gerber sulfuric acid :( specific gravity 1.823) at 15-21c into Gerber Butyrometergravity 1.823) at 15-21c into Gerber Butyrometer. .

22 . .Add 1ml of isoamyl alcohol and insert the lock Add 1ml of isoamyl alcohol and insert the lock stopper grasp the test bottle at the graduated stopper grasp the test bottle at the graduated

column and shake it until the curd is completely column and shake it until the curd is completely digesteddigested..

33 . .Adjust temperature of the milk sample to 22-Adjust temperature of the milk sample to 22-21C21C.°.°

44 . .Transfer 11ml well mixed milk sample to Gerber Transfer 11ml well mixed milk sample to Gerber test bottletest bottle..

55 . .Place them in a Gerber centrifuge close the Place them in a Gerber centrifuge close the cover and lock. After the required speed 1500 rpm cover and lock. After the required speed 1500 rpm

centrifuge for 5mint stop the centrifugecentrifuge for 5mint stop the centrifuge..66 . .Directly read the fat in Gerber butyrometer and Directly read the fat in Gerber butyrometer and

describe result in fatdescribe 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 fat% in milk minimum

 Cows 3%

Buffalo 5% Sheep 4% Goat 2.5 %

Purpose of Gerber test

 ( Causes of decrease fat )%

*Add water to the milk • *extract or remove the fat from the milk (skim

milk) *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+1oC and mixing.  Sample and weigh milk at 38+1oC.

• 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+1oC 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+1oC.  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+1oC.  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.