Butter fat testing using Gerber method is one of the many quality assurance test procedures carried out in milk. It is a simpler modification of the Babcock method with special butyrometers for various dairy products.
Butter fat determination is necessary to determine the amount of butter fat present in milk and milk based products.
One can be able to conduct a butter fat test on fresh milk, fermented milk, cream, etc.The Gerber method is the most widespread and direct method of butter fat content analysis in milk Click To Tweet
Advantages of butter fat testing using Gerber method
- Simple/easy to use
- Very fast
- You read the results directly
Disadvantages of the Gerber method
- Needs expertise
- Required equipment are costly.
The principle of butter fat testing using Gerber method
The centrifugal force exerted in the mixture separates the lighter fat portion from the heavier non-fat portion of the milk. Sulfuric acid dissolves the protein that encapsulates the butterfat (fat globule membranes). Amyl alcohol provides a clear distinction between the fat and non-fat portions.
Before we go into the technical aspects of butterfat testing, we should ask ourselves one question:
What are the sources of fatty acids that constitute butterfat?
The milk butterfat comes from three major sources/pathways, namely:
- Synthesized by the mammary gland from acetate and B-hydroxybutyrate that are produced by the rumen bacteria. These are majory composed of short chained fatty acids and some medium chained fatty acids. The chain length differs among species and is controlled by the specificity of the enzymes involved in the removal of fatty acids from the synthetase complex. This is the major source of fatty acids in butterfat synthesis.
- Fatty acids synthesized from glucose via glycolysis, citric acid cycle, and cleavage of citrate leading to formation of acetyl coenzyme A and oxaloacetate. This pathway leads to formation of only minimal amounts of fatty acids in milk.
- Fatty acids can also come from pre-formed fats that are transferred to the mammary gland via blood and lymph. This pathway leads to formation of long-chained fatty acids of 16 carbons or more.
What is “low-fat-syndrome” and how do you deal with it?
Animals fed on low-roughage diet have diminished acetate and increased propionate production in the rumen. As a result, they produce milk whose butterfat content is nearly half the content of butterfat from cows fed on high-roughage diets.
Due to low acetate, the former can only produce minimal proportions of short and medium-chained saturated fatty acids hence low butterfat content in the milk they produce.Low fat syndrome is when a cow produces milk with low #butterfat content. #lowfatsyndrome Click To Tweet
To address this problem, cows should be fed on high roughage diet to promote synthesis of acetate, which is responsible for synthesizing short and medium chained fatty acids.
Equipment and materials you will need for butter fat testing using Gerber method:
- Sulphuric acid (density 1.807 – 1.812 g/ml at 270C, colourless).
- Amyl alcohol (specific gravity 0.815-0.818).
- Butyrometers: 6%, 8% and 10% scales depending on the sample fat content. (Ensure they have proper stoppers).
- Automatic acid dispenser (use 10 ml acid pipette in the absence of an automatic dispenser) for sulphuric acid.
- 10.75 ml pipette for milk sample.
- 1 ml pipette for amyl alcohol.
- Gerber centrifuge (you can also use a hand driven centrifuge in the absence of an electric one). Gerber centrifuge are the best (like the one in the anchor image) because they are self heated hence will eliminate the need for a water bath.
- Water bath at 650C (in the absence of a Gerber centrifuge)
Procedure for milk butter fat testing using Gerber method#Butterfattesting Why do we use 10.75 ml of milk for the #Gerber method? Learn more... Click To Tweet
The most reliable, straightforward method is the Gerber butterfat test method, and it is conducted as follows:
- Add 10 ml of Gerber acid into the butyrometer followed by 10.75 ml of the milk sample and then 1 ml of amyl alcohol.
- Cork the butyrometer tightly and mix the contents. This helps to dissolve all the Milk solid Non Fat (MSNF) and separate the fat.
- Balance the butyrometers in the Gerber centrifuge and run it for 5 minutes. (Gerber centrifuge is self heating; the fat remains liquid)
- After centrifuging the butyrometer, read the butterfat content directly on the stem.
Why do we use 10.75 ml of milk for the Gerber method?
The principle relies on the weight of fat in the sample. For each 1% callibration of the butyrometer, there will be 0.125ml of fat.
This means that the weight of the fat content is equivalent to the volume X density; 0.125 x 093 = 0.1125.
Now, if 1 % graduation represents 0.1125g then 100 % will give us 11.25g of the fat content.
Milk has an average specific gravity of 1.032, you should use 11.25 / 1.032 = 10.9 ml of milk. There are impurities introduced by the isoamyl alcohol (about 2.5%) into the sample that will affect the reading.
Again, there is also some residual volume of milk left in the pipette, hence the pipette calibration to 10.75 ml.
Functions of Gerber’s acid (conc sulphuric acid) includes the following:
- Digests casein and organic matter in milk to facilitate fat separation. The differences in density between the acid and fat will make the distinction clearer during and after centrifuging.
- Adding milk into the acid produces an exothermic reaction. The heat produced melts the fat and reduces its viscosity. This makes its quantity easy to determine on the butyrometer stem.
How to determine butter fat content in a cheese sample
When determining the butterfat content of cheese, add the 10 ml Gerber acid and follow with cold distilled water.
Ensure that, while topping up with water, the level reaches the 6 mm mark.
After that, weigh 3 g of the cheese sample and add into the butyrometer followed by addition of 1 ml of amyl alcohol.
Shake to dissolve all the contents after securely corking it.
Finally, centrifuge using the procedure outlined above to determine the butter fat content.
The video below illustrates how you should carry out the butter fat testing using Gerber method.
Modern centrifuges are self-heated, so you don’t need to put the butyrometer into the water bath after centrifuging.
Problems/Defects of butterfat testing
The most common defect you can encounter while testing for butterfat content is charring. This is when you observe black specs at the lower fat/non-fat interface of the butyrometer contents.
Possible causes of this defect include:
|Possible cause of charring||How to avoid|
|The acid is either too strong or too much||Reduce the volume of acid used or use an equivalent quantity of weaker acid|
|Pouring milk directly into the acid||Hold the butyrometer at an angle to allow the milk to flow on the side of the bottle|
|Failure to mix the acid and the milk evenly||Ensure all the mix thoroughly mixes (use a rotary motion to achieve this). Take caution because the reaction is exothermic|
|Too warm milk or acid||Temper to between 15°C and 20°C.|
The other defect of butter testing that is closely related to the first one is the presence of a light colored fat column. You may also observe light colored specs at the bottom of the fat column. This may affect your reading of the butyrometer column when performing butter fat testing using Gerber method.
Here are the causes and remedies
|Possible causes||How to avoid|
|The acid is either too weak or too little||Increase the volume of acid used or use an equivalent quantity of a stronger acid|
|Failure of the curd to dissolve completely before you start centrifuging||Ensure all the curd thoroughly dissolves (Thoroughly mix it up in a rotary motion).|
|Too cold milk or acid||Temper to between 15°C and 20°C.|
While working in the lab, you must abide by the laboratory safety rules. Wash off any acid spills on skin with plenty of water.
Always practice safe disposal of the acid contents after the experiment. The acid may corrode the plumbing works.
Reasons for butterfat content variations in milk from cows of the same breed
Ideally, cows of the same breed should produce milk with a consistent butterfat content. However, that is not the case. You will notice that the butterfat content varies widely and these are some of the possible causes of this variation:
Butterfat content varies from cow to cow based on some individual traits and other prevailing conditions. It is a natural occurrence.
Stage of lactation
Healthy cows hit their peak in butterfat production immediately after parturition. The content reduces regularly until it hits its lowest after 60 days. From that point, the butterfat content begins to increase again until it hits the peak at the end of the lactation period.
Age of the cow
As the cows advance in age, they experience a slight uniform decline in butterfat production. It is perfectly normal.
Heat period (oestrus)
The hormonal imbalance that comes with estrus affects milk production. While there is an observed drop in milk production, the milk has a slightly higher butterfat content.
Season of the year
Butterfat is highest during dry seasons when the animal has plenty of roughage than during rainy/cold seasons when the amount of dry matter intake drops.
Time/frequency of milking
When milking regularly, e.g. twice a day, the morning milk will have a lower volume but higher butterfat content than the evening milk. The cow’s system has adequate time at night to create more butterfat due to reduced activity.
Prevailing weather conditions
Cool weather favors production of more milk with higher butterfat content than hot humid weather.
Feeds and nutrition
Cows that feed on balanced diet will produce more milk that is rich in butterfat content than those that lack crucial nutrients in their diet.
Other contributors to butterfat variation that can affect butter fat testing using Gerber method
- Frequency of milking and complete emptying of the udders
- Health of the animal
- Milking methods used
- Disturbances/excitement level of the animal