On milk treatments.
Raw, thermised, pasteurised, UHT heat treatments.
Raw milk contains harmless bacteria in a completely normal way. Among this normal milk flora, we find the famous lactic acid bacteria which have technological utility since it is these strains of bacteria which are used to ferment milk and produce yogurt or cheese. They also play a certain role in protecting raw milk against pathogenic bacteria by occupying space ( microbiological competition or the Jameson effect ). These bacteria feed on the sugars, fats and proteins in milk to produce complex flavour compounds and acids, which are sought after in the production of cheese or yogurt. Raw milk has been found to harbour over 150 types of microorganisms.
Advantage: Its diverse microbiological flora contributes in maintaining a healthy microbiota.
Disadvantage: Low shelf drive, 3 to 5 days, possible presence of pathogens harmful to groups at risk.
Thermisation:
Thermised milk is milk that is heated for a minimum of 15 seconds to a temperature between 57°C and 68°C. It is usually performed by cheese makers who do not own a dairy farm and do not have direct access to raw. There may be a slight increase in pathogen numbers and the maker will thermise in order to reduce these numbers and maintain though a certain diversity by not killing everything.
Advantage: Thermisation makes it possible to preserve a taste and nutritional value which are closest to raw milk.
Disadvantage: Part of the enzymes and microflora will continue the progressive degradation of the milk, leading to shorter storage than for other more violent heat treatments.
Pasteurisation:
Pasteurisation is the heat treatment of the “softest” milk. It involves heating the milk to a temperature between 72°C and 75°C for 15 seconds then cooling it immediately or let it cool by itself a the cheese making vat. This gentle treatment eliminates all possible pathogenic and active enzymes while not altering in a too drastic manner the structure of the milk. This is the technique used by pasteurised milk cheese makers.
Advantage: The shelf life is between 21 and 30 days. Pasteurisation would be the treatment which makes it possible to preserve the structural quality of milk and allows for the creation of quality cheeses.
Disadvantage: Pasteurised cheeses are re seeded with selected micro organisms for the purpose of cheese making. They are not as microbiologically diverse as the two above, they may not therefore inhibit pathogen proliferation by biological competition ( Jameson effect ).
High pasteurisation:
Halfway between classic pasteurisation and UHT treatment in terms of temperatures, high pasteurisation uses higher temperatures (between 85 and 134°C) which destroy all the germs.
Advantage: The shelf life is between 21 and 30 days.
Disadvantage: The shelf life is shorter than for UHT milk. Milk treated by high pasteurization is not sterile and must therefore be stored in the refrigerator.
UHT treatment
Developed in Switzerland in 1951 and adapted at the industrial level in 1962, the UHT process was a real revolution in the dairy industry. UHT are the initials for High Temperature Uperization, since simplified to Ultra High Temperature.
Principle: The milk is brought almost instantly to a very high temperature (between 140 and 150°C) for a very short time (2 to 5 seconds) and it is stored in anaerobic packaging ( absence of oxygen ). The product is considered sterile.
Advantage: UHT treatment allows the milk to be preserved for a very long time, around 3 months or even more. A big advantage for consumers but even more so for distributors, UHT milk can be stored without problem at room temperature, making it possible to drastically reduce logistics and storage costs. Curiously, in the era of sustainable development, we frequently find it unnecessarily filling the fridges of certain department stores... Disadvantage: Slight modification of taste, depending on the processes used (indirect UHT). Requires packaging impermeable to light and oxygen. In the case of cardboard cartons, an aluminium foil is added, generating an additional ecological cost compared to cardboard packaging for other milks.
Homogenized & standardized mechanical treatments.
Homogenised:
milk fat globules naturally tend to rise to the surface to form a creamy layer, floating on the leaner phase of the milk. This property of fat poses a problem in the case of drinking milk because the fat would float in the consumer's glass or would remain partly stuck to the wall of the milk carton. The homogenisation process consists of breaking the fat globules into fine particles. To do this, the milk is passed through a nozzle with a pressure of 100 bar for milk intended for pasteurisation and a pressure of up to 250 bar for milk intended for ultra-high temperature (UHT) heating. Temperature and pressure determine the size of the fat globules resulting from this treatment. These do not rise to the surface, but are distributed homogeneously in the aqueous phase of the milk, which prevents the cream from separating even after storage for several days
Standardised:
the level of fat naturally present in milk is variable. It depends on several factors such as the breed of cattle, the cows' diet and the seasons. Drinking milk, for its part, often has a fat content that has been voluntarily adjusted to a certain percentage; we then speak of standardised milk. The adjustment is made by mixing whole milk and skimmed milk until the desired fat content is obtained.
Whole, semi or skimmed mechanical treatments.
The difference between these 3 categories is the level of fat present in milk, the fat may have been removed and added to bring it to a standardised value.
Whole milk: This is basically milk containing all of its fat, generally varying around 3.9% and more, in particular for milk from cheese-producing cows. It can be standardised but its fat content must, in all cases, be greater than or equal to 3.5%. Thus, the majority of whole milks are standardised at a minimum of 3.5% in order to recover the fat for resale. Note that the standardisation of whole milks was authorized a few years ago in order to harmonize legislation with European regulations. Standardisation is therefore authorized, but is not obligatory. Dairy processors did not hesitate to take advantage of this to make their butter with the fat they remove from milk. Non-standardised whole milk has become rarer.
Semi skimmed milk: As its name suggests, this type of milk has been standardised and now only contains a portion of its original fat content. Its fat content averages between 2% or 2.7%.
Skimmed milk: AKA low-fat milk, is milk that has been deprived of almost all of its fat and must have a fat content equal to or less than 0.5% fat. Many commercial skimmed milks have a fat content of 0.1% fat.
Some sources:
http://www.agroscope.admin.ch/data/publikationen/1313495031_217.pdf
(http://www.db-alp.admin.ch/fr/ueberuns/faq_detail.php? id=85
http://www.rts.ch/emissions/abe/alimentation/1371022-lait -bouillu-lait-foutu.html
What to choose, France, “Choose the right bottle of milk” Agroscope, nutritional values of milk: http://www.agroscope.admin.ch/trinkmilch/index.html?lang=fr