Assessing the quality of liquid milk is done through performing quality assurance tests, which begin by sampling of the liquid milk. It is important for safety and economic reasons. All dairy products must be tested for quality assurance purposes.
The objective of raw milk quality assessment is to ascertain the quality of the finished product. You have to make sure that you are starting off with the best quality raw milk so that you can assure the consumers that the quality of the finished product is the best.
Since you are dealing with large quantities of milk, it is necessary to take a representative sample from which you will be able to vdetermine the quality of the entire batch. This is why you will need to do sampling of liquid milk.
Sampling liquid milk from a single container
At the processing plant, you will be receiving milk in single batches, either from individual farmers or from bulking stations. You will need to obtain samples from these single containers.
To do this, mix the milk mechanically and then draw the required quantity of sample. Label the sample container appropriately and follow the general sample handling procedures.
Sampling liquid milk: collecting a composite sample from several containers
A composite sample is the quantity of milk obtained by mixing proportional parts of different milks. A sample is then picked from the composite sample to represent the whole lot.
Sampling liquid milk from storage tanks and road tankers
Storage tanks usually have agitators used to mix the milk. Ensure the milk is mixed gently for about 15 minutes in the tank and in case there are no mechanical agitators, mix the milk mechanically using a stirrer and then pick the sample using a dipper.Careful sampling is the root of proper quality assurance in dairy processing #dairy #yoghurt #cheese Click To Tweet
Pick the samples proportionate to the size of the tank. The minimum amount of the sample should be at least 500 mls.
Most modern tanks and tankers have automatic samplers from which you obtain the sample after the contents have been uniformly mixed.
Sampling Different Dairy Products
a) Sampling cream
Cream is thicker than fluid milk; therefore, the tester should use a sampling tube with a wider diameter. It is important to ensure that the cream has been properly mixed before picking the samples.
Make sure to examine the samples soon after collection as any delay may lead to deterioration in the sample quality. This is due to the susceptibility of cream to enzymatic degradation given its high butter fat content. This could jeopardize the results.
b) Sampling evaporated milk
Put the unopened cans in a water bath at 60°C for two hours. You will need to remove the cans from the water bath every 20 minutes for a vigorous shaking.
After the two hours have elapsed, remove the cans and cool to room temperature. Remove the lid and mix the content with a spatula. At this point, you can get a composite sample from different cans.
Depending on the type of tests to be done, you can test the sample the way it is or you can mix with distilled water. The value obtained from the test is adjusted using a correction factor.
c) Sampling sweetened condensed milk
Temper the unopened cans in a water bath at 35°C for 30 minutes. After the time has elapsed, empty all the contents of the container while still warm and mix to a uniform consistency.
Take 100 grams of the sample and mix with 500 grams of distilled water in a water bath. Get a test sample from the diluted mixture for testing and correct using the dilution factor used.
d) Sampling dried milk
Avoid sampling in a high humidity environment. Take samples from different parts/regions of the mass to be tested using a tubular trier and then transfer the collected samples to a dry clean container and seal immediately.
Roll and invert the container to make the sample homogeneous. If there are lumps, sieve the sample, grind the residue and sieve again. Test immediately or keep the sample in an airtight container for analysis at a later date.
Under some circumstances, it may be necessary to keep the sample in an opaque container.
e) Sampling butter
Take samples from a batch of bulk butter using a stainless steel trier from the different sections, which you will then mix to obtain a homogeneous sample.
You may soften the samples by warming in a water bath at 38°C while checking the sample regularly during this process. After it has obtained the required texture, weigh the required quantity and carry out the tests.
When you are sampling packaged butter, pick packets from different areas in the storage room. Combine all these samples together to obtain a homogeneous mix from which you will get the test sample.
f) Sampling cheese
For small pieces of cheese take the entire cheese block while for the larger cheese blocks, obtain samples using triers that reach into the centre of the cheese block.
For hand cheese, cut or shred the cheese using a food chopper then mix before getting a representative sample.
g) Sampling ice cream and other frozen dairy products
Allow the sample to soften to room temperature and then mix for about two minutes in a blender. Obtain the test sample and conduct the required test procedure.
If the ice cream or the frozen dairy product contains fruits and/or nuts, mix in a high speed blender for about seven minutes to make sure that it is fully homogeneous before obtaining the test sample for conducting the required tests.
h) Sampling pasteurized milk
For retail packages, pick a number of packages but for bulk packaging, mix the bulk and take 500 mls as a representative sample.
When sampling from closed systems (e.g. UHT), there will be an inbuilt sampling equipment or mechanism on the system for taking the samples aseptically.