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Gerber's method: Butyrometric determination of fat content in untreated and pasteurized milk
The Gerber method is rapid testing method by which the fat content in milk is determined using a Butyrometer. It is still used today in farms and in dairy laboratories despite the introduction of automated methods. The advantages of Gerbers method over modern rapid testing methods are:
  • Omission of the need for time-consuming calibration of the measuring gauge 
  • Relatively low investment costs and hence low costs in performing quick tests on individual samples
  • It cam be used on all types of milk
CHEMICALS NEEDED:
- Sulphuric acid 90%
- Amyl alcohol 98%

EQUIPMENT:
- Calibrated butyrometer with suitable stopper
- Pipette for milk 10.75 or 11ml
- Measuring tap for 10 ml sulphuric acid
- Measuring tap for 1ml amyl alcohol
- Heatable centrifuge
GENERAL PROCEDURE

Preparation of the test specimen:
  • Bring the milk sample to 20ºC and mixed well to get an homogeneous distribution of the fat on the sample.
  • Let the sample stand for 3 minutes to allow any pockets of air to disperse. 
Procedure:
  • The same milk specimen must be tested twice.
  • Make ready two milk butyrometers and add 10 ml of sulphuric acid in each with the measuring tap without wetting the neck of the butyrometer.
  • Then pipette 10.75 or 11 ml of milk into the butyrometer in such a way that the butyrometer neck does not get wet and the milk does not mixed with the sulfuric acid (A clear dividing line between the acid and the milk, without a brownish-coloured edge, is a good sing of good layering)
  • Add 1ml of amyl alcohol with the measuring tap. Be careful to avoid mixing of the liquids.
  • Close the butyrometer with the stopper carefully.
  • Place the butyrometer in a butyrometer stand and shake vigorously until all liquids are thoroughly mixed. When the liquids are mixed a considerable a mount of heat and gas are produced. This can cause the stopper to shoot out or the butyrometer to break. Be attentive to all the safety measures.
  • Immediately after mixing place the butyrometers inside the heated centrifuge upsidedown. The butyrometers must be placed exactly opposite each other. Centrifuge 65ºC at 1100 for 4 minutes.
  • Remove the butyrometer from the centrifuge without turning them and read results. 
Reading the results:
  • After removing the butyrometer from the centrifuge it should be held vertically at a high where the meniscus of the column of fat is at eye level.
  • With the help of the stopper locate the line between the residual mixture and fat on a subdivision of the butyrometer scale and read off the high of the column of fat at the lowest point of the meniscus.
  • The result should be given in mass percent.
 
 
 
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SACHET
UNDER CONSTRUCTION

The Dairyman's
ten commandments

Gerber's Method
Butyrometric determination of fat content in untreated and pasteurized milk

 
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