Dairy Science
Automated Milk Analysis and Calibration
Hi, Milkfans
 When doing any automated milk analysis you must remember that the apparatus is calibrated against a certain referance. It is not wise to test cow’s milk on an apparatus that has been calibrated with goat’s milk or vice versa. This has to do with the different sizes of the fat globules, etc.
This is also the reason that ( I think) that goat’s milk digest easier than cow’s milk. It has nothing to do with goat’s milk not having any lactose – that’s nonsense.
 All for today,
Leon the Milkman
Â
UHT Milk Problems
Hi, Milkfans
UHT milk translates to “Ultra High Temperature” Milk and is also known as long-life milk.
It is made by pasteurizing at something like 132-150 degrees Celsius for a second up to 15 seconds.
To prevent problems it is important that the milk is not going sour, that it has the right salt balance and that there is not too much serum proteins ( colostrum ) in the milk.
Put into practice you should get an analysis of salts in “normal” milk and what variance is allowed to test the milk against. Also make sure the farmer does not have too many cows calving at the same time to prevent high colostrum in the milk.
It is a good idea to do an Alcohol Test on the milk with an alcohol strength of 72-75% alcohol. This will give a fast and accurate indication of the heat tolerance of the particular milk.
Regards,
Leon the Milkman
Density vs. Specific Gravity of Milk
By determining the specific gravity (SG) of milk the following information can be obtained.
• An indication of adulteration of milk with added water.
• If the fat percentage is available the solids-non-fat (or total solids content) of the milk can be calculated.
- Definition
Specific gravity is the relationship of the mass of a specific volume of a substance to the mass of an equal volume of water at the same temperature.
Density is measured as mass per volume (g/ml) at a specific temperature.
The specific gravity of milk at 20 °C is ± 1.030 and is determined by the relative proportions of fat (SG = 0.93), water (SG = 1.0) and solids-non-fat (SG = 1.614).
Kind regards,
Leon the Milkman
Calorie vs. calorie
Hi, Milkmen and Milkmaidens
Have to do a calorie count for a product label?
Here in South Africa we use kiloJoules and the conversionfactor to get that to Calories is to devide by 4.2.
Thus 100 Cal amount to 420 kJ.
Check this difference though: calorie is the energy it takes to heat one gram of water one degree Celsius, and a Calorie(used in Food Industry) is actually a kiloCalorie(1000 Cal.) that has no relation to a calorie. :-), but is equal to 4.2 kJ.
Got it all figured,
Leon the Milkman
The case of Psychrotrophic bacteria
Psychrotrophic bacteria seem to be becoming the newest thorn in the side of the dairy industry. Scary bit is that we are helping them along.
“How?†do you ask?
Because of economic factors the pre-processing time of raw milk has been extended to an average of 4 days. This allows ample time for psychrotrophic, proteolytic bacteria to grow, and form heat stable enzymes. Although the psychrotrophic bacteria are easily killed off by normal pasteurization temperatures, the formed enzymes can survive UHT processes.
This causes multiple problems and we here at Elsenburg Dairy Lab have especially seen those problems on products like cottage cheese and UHT milk, more so over the past few years.
This is a group of bacteria that actually loves the cold chain, as it helps them outwit, outlast and outperform their competition. 😉
Nowadays psychotropic bacteria predominate in raw milk in the cold chain, especially Pseudomonas spp.
So much so that when the same milk is plated out and incubated at 7° C and at 30° C(as in Total Plate Count), the psychotropic growth will overtake the mesophilic growth, causing psychrotrophic counts to be higher than total plate counts.
I don’t think the methods of analysis are of much importance in this article, because there are many, ranging from microbial(determining the bacteria) and biochemical(determining the formed enzyme). Qualitative tests are of no use as we want to be able to enumerate the psychrotrophic bacteria.
The main concern I have is to raise awareness of a fast growing problem, that will only become more so in the future.
Possible solutions are the following:
1) Ask your lab to do a monthly psychrotrophic count on all farmers. This will identify
your high risk milk supply.2) Thermising the milk to 68° C before cooling on the farm. This would have to be done with a plate heat exchanger, but would be economical at this stage, because the milk is already at body temperature(37° C) and the treated milk can run against the incoming milk to heat it and to be cooled down itself. An ice bank would also be needed to finish the cooling process. The thermising process would obviously increase the overall quality of
the milk as well, without influencing heat stability to a large degree.
3) Very rapid cooling on the farm to 2° C, instead of the usual 4° C and keeping it there until processing.
4) Using a pre-cooler at the factory to cool the milk down quickly from the 5-7 °C that it arrives at, to 2 °C.
Kind regards,
Leon the Milkman
Freezing Point
Hi, Milkfans
The freezing point of milk is used to detect added water. As you should know water freezes at 0° C and because milk has some salts and lactose that are in solution the freezing point of milk is slightly lower than water – to the point of about a half a degree Celsius.
In fact for the test, the freezing point of milk should fall between -0.512° C and -0.550° C. If it is closer to zero water is added and if it lies beyond -0.550° C the milk is either going sour or solids, like whey powder was added.
Kind regards,
Leon the Milkman
Cheese Yield vs. Milk Solids
Hi, Cheesefans
This is a topic not many lay cheesefanatics know about: the influence of milk solids on the yield of cheese.
The higher the Solids – being Fat, Protein( these are the ones important in cheese making) – the higher the yield of cheese out of a certain volume of milk.
Generally cow’s milk gives a higher yield than goat’s milk.
Thus you need more goat’s milk to make a kilo/pound of cheese than you would with cow’s milk.
Kind regards,
Leon the Milkman
Â
Â
Cheese Yield and Factors Affecting Its Control: Proceedings of the IDF Seminar Held in Cork, Ireland
Density vs. Specific Gravity
Hi, Milkfans
Density is measured as mass per volume (g/ml) at a specific temperature.
Specific Gravity is the relationship of the mass of a volume of a substance to the mass of an equal volume of water at the same temperature.
In dairy both the density and the specific gravity are influenced by the fat percentage and the SNF-percentage.
Top of the day to you,
Leon the Milkman
Yeast in cheese.
Hi, Cheesefans
If you made cheese and you end up with a spongy curd that smells like beer brewing, bread or pineapple when you press on it and smell close by at the same time, then it is a pretty sure thing that you have yeast in that curd. To confirm you will have to have a yeast-and-mold test done at a microbiology lab. This takes a full 5 days.
You’ll have to make processed cheese 😉
Kind regards,
Leon the Milkman
Holes in cheese
Hi, Milkfans
Two types of holes to be found in cheese. The one is a mechanical , irregular hole, mainly caused by too little pressure. The other is a gashole which is round, smooth and shiny, and is caused by bacterial growth( hopefully the good kind).
Regards,
Leon the Milkman
Follow me on 