The Gerber method is a primary and historic chemical test to determine the fat content of substances, most commonly milk and cream.[1] The Gerber method is the primary testing method in Europe and much of the world.[2] The fairly similar Babcock test is used primarily in the United States, although the Gerber method also enjoys significant use in the U.S. as well.[3]
The Gerber method was developed and patented by Dr. Niklaus Gerber of Switzerland in 1891.[4]
Milk fat is separated from proteins by adding sulfuric acid. The separation is facilitated by using amyl alcohol and centrifugation. The fat content is read directly via a special calibrated butyrometer. Gerber developed specialized butyrometers (tubes), pipettes, and centrifuges. Water baths built specifically for the Gerber tubes are often used.
The test is still in widespread use today and is the basis for numerous national and international standards such as ISO 2446, International Dairy Federation (FIL) Regulation 105, BS 696 (United Kingdom), and IS 1223 (India). Larger facilities may prefer to use faster analysis techniques such as infrared spectroscopy as these greatly reduce the potential for user error and reduce the time and COSHH requirements.
The test continues to be improved and standardized.[5]
The two major defects associated with the Gerber method include:
- Charring – is observed as tiny black specs at the fat/non-fat interface in the butyrometer. This problem is due to charring of the milk proteins by the concentrated Gerber acid. It could also arise as a result of pouring the milk sample directly onto the acid in the butyrometer. To avoid charring, first, ensure the acid concentration is right. Secondly, while adding the milk sample, let it flow on the side of the butyrometer to avoid violent reaction when it drops on the surface of the acid.
- Light colored fat column (with or without brown specs at the interface) – may affect one's ability to read the fat content correctly. This problem is due to weak acid, which fails to dissolve all the milk non-fat content. To avoid this problem, use sufficient volumes of the Gerber acid at the correct concentration.
Ionel Rosenthal; Uzi Merin; Gita Popel; Solange Bernstein; Amnon Kadman (1985). "An Analytical Assay for the Determination of Oil Content in Macadamia". Agricultural Research Organization, Israel. Archived from the original on 16 May 2008. Retrieved 4 September 2008. Fast and accurate test methods were developed for this purpose. Two, basically similar, methods are in use: the Gerber and the Babcock methods (Atherton & Newlander. 1977). The Gerber method is the standard one in most European countries, whereas the Babcock is more common in many states of the U.S.A., although the Gerber method is also employed. Both methods are based on the digestion of all milk components, except oil, by concentrated sulfuric acid and the separation of the oil from the aqueous phase by centrifugation in special glassware, called butyrometers. In addition to fluid milk products, the Gerber test can be used for the assay of fat in cream, concentrated milk, ice cream, cheeses, and sausages (Pearson, 1970), provided that special both-ends-open butyrometers are employed. The very similar Babcock method, with various digesting reagents, has been applied satisfactorily to fish products (Horwitz, 1975).
James, Ceirwyn S. (1994). Analytical Chemistry of Foods. Springer. pp. 50–51. ISBN 978-0-8342-1298-5. Retrieved 28 August 2008. Gerber method. This is a method used extensively in the UK and Europe for the routine estimation of fat in dairy products. Specific Gerber tubes, or butyrometers, have been designed for specific dairy products such as whole milk, skimmed milk, cream and cheese. Methods have been developed for these particular products and also for other dairy products, such as butter and ice cream, by using butyrometers designed for one of the above specific products and modifying the procedure for the alternative products. Thus, the fat content of butter may be measured by using cream butyrometers and that of ice cream by using whole milk or cheese butyrometers, appropriate modifications to the method being undertaken.
The procedure involves measuring a specified amount of dairy product into the butyrometer, and adding concentrated sulfuric acid (to dissolve the non-fat milk solids) and amyl alcohol to aid the separation of fat and aqueous phases. Water is added where necessary to bring the liquid levels to a point where the fat level is on the scale. The addition of the sulfuric acid causes the temperature of the mixture to increase and the fat to liquif, additional warming in a water bath is occasionally necessary to effect complete liquifying of the fat and also the solubilisation of the non-fat solids. The mixture is centrifuged in a special Gerber centrifuge for a set time at 1100 rpm, and then the tubes are placed in a water bath to standardize the samples before the fat reading is read off the calibrated scale of the butyrometer.
James, Ceirwyn S. (1994). Analytical Chemistry of Foods. Springer. pp. 50–51. ISBN 978-0-8342-1298-5. Retrieved 28 August 2008. Babcock method. The principle of the Babcock method is similar to that of the Gerber described above. It differs from the Gerber method in the nature of the glassware used and in the specification of dividers or calipers to measure the length of the fat column. The Babcock method is widely used in the USA.
Badertscher, René; Thomas Berger; Rolf Kuhn (January 2007). "Densitometric determination of the fat content of milk and milk products". International Dairy Journal. 17 (1). Elsevier Ltd: 20–23. doi:10.1016/j.idairyj.2005.12.013. The fat content of a milk product is an important indication of quality, both economically and physiologically. In the dairy industry, it is mainly determined by using quick methods. Spectrometric measuring methods are often used. However, these methods have to be calibrated, which is costly. Many laboratories, therefore, are using a method developed by the Swiss chemist and dairy-owner Niklaus Gerber, patented in 1891 under the name Acid-Butyrometrie. This method is still used because it is simple, fast, low-cost and suitable for a relatively high sample throughput. However, butyrometry has several disadvantages. The determination cannot be automated and involves a certain risk in handling highly concentrated sulphuric acid, especially while reading the butyrometer. Handling the butyrometer requires practical skills, which has a negative effect on the robustness of the method. A great disadvantage is the varying definition of fat compared with the reference methods. In the latter, fat is always defined by extraction with a non-polar solvent. In the butyrometric method, this extraction step is missing. Several attempts have been made to harmonize the fixed butyrometer scale with the values from reference analysis. Even with the costly gravimetric reference methods, attempts were made to automate or simplify the procedure.
"Association of analytical chemists (AOAC) recommends Gerber test". Dairy Field. Stagnito Publishing. July 2002. Research was recently published in the Journal of AOAC International, which concludes that the Gerber method be adopted as an official first action for testing butterfat in whole milk. The Gerber method is used worldwide as a simple and rapid method for determining the fat in raw and processed milk. It was first recognized in the United States in 1960 and remains an approved volumetric procedure in Standard methods for the Examination of Dairy Products. However, it had never gained status as an official method by AOAC. Additionally, the volume of the test portion has not been internationally agreed upon.
