Varieties of Milk
Varieties of milk
There are many different varieties of milk available for consumption within the UK.
The different milks tend to vary according to the way they are produced, and in their fat content.
Which milks are available?
Natural whole milk is milk with nothing added or removed.
Whole standardised milk is whole milk standardised to a minimum fat content of 3.5%.
Some EU member states may produce an additional category of whole milk with a minimum fat content of 4%.
Whole homogenised milk is identical in fat and nutrient content to whole milk or whole standardised milk however it has undergone a specific process known as “homogenisation” which breaks up the fat globules in the milk. This spreads the fat evenly throughout the milk and prevents a creamy layer forming at the top.
How is it produced?
Natural whole milk is collected from the dairy herd and undergoes various processing techniques before it reaches the shelf for consumption by the general public.
Most of the milk consumed in Europe, Scandinavia, the USA, Australia and New Zealand is pasteurised.
Pasteurisation is the process whereby milk is heated with the purpose of killing potentially harmful micro-organisms such as certain pathogenic bacteria, yeasts and moulds which may be present in the milk after initial collection. This helps to protect against any food bourn illness that can occur through consumption of raw (unpasteurised) milk.
Following pasteurisation, the milk is rapidly cooled and is then stored in a refrigerator in order to preserve its shelf life.
Various pasteurisation and heat treatment techniques can be used in the production of milk which can affect storage capacity.
Much of the milk in the market is now homogenised as well as pasteurised. Homogenisation offers a way to reduce the fatty sensation of whole milk and prevent the formation of a cream plug.
Semi skimmed milk
Semi skimmed milk is the most popular type of milk in the UK with a fat content of 1.7%, compared to 4% in whole milk and 0.3% in skimmed milk.
Skimmed milk has a fat content of between 0.1-0.3 %. Skimmed milk therefore has nearly all the fat removed.
It contains slightly more calcium than whole milk and lower levels of fat soluble vitamins, particularly vitamin A, as this is lost when the fat is removed
The lower level of fat in skimmed milk reduces its calorie (energy) content. For this reason it is not recommended for children under the age of 5 years as they need the extra energy for growth. However it is ideal for adults who wish to limit their fat or calorie intake.
Skimmed milk has a slightly more watery appearance than other types of milk and has a less creamy taste due to the removal of fat.
Organic milk comes from cows that have been grazed on pasture that has no chemical fertilisers, pesticides or agrochemicals used on it.
The producers must register with an approved organic body and are subject to regular inspection.
Once the cows have been milked, the milk is treated in exactly the same way as regular pasteurised milk.
There is no evidence to suggest that organic milk is any more nutritious than conventionally produced milk. Although there have been studies to show that organically produced milk contains higher levels of omega-3 polyunsaturated fatty acids, these are plant derived, short-chain fatty acids which appear to be of limited health benefit compared to the longer chain omega-3 fatty acids found in oily fish.
Jersey and Guernsey milk
Channel Island milk is produced from Jersey or Guernsey breeds of cow and has a particularly rich and creamy taste.
It tends to be slightly higher in calories and fat than regular whole milk and also has a higher content of fat soluble vitamins -particularly vitamin A which is important for the promotion and maintenance of healthy growth and development.
Jersey and Guernsey milks tend to have a visible cream line and are commonly found in supermarkets as “breakfast milk”.
The flavoured milk market is one of the fastest growing dairy sectors.
There are a wide variety of flavours and consistencies to cater for all ages and tastes with a choice of long-life (i.e. Ultra Heat Treated or sterilised) or fresh flavoured milk.
Most flavoured milk products are produced using reduced fat milk varieties and usually have a fat content of around 1%.
The most popular flavours are chocolate, strawberry and banana however more sophisticated flavours such as peach, mocha or products made with real Belgian and Swiss chocolate have been developed for the more adult market.
In comparison with plain milks, flavoured milks tend to have slightly higher sugar content, however studies have suggested that they are still a favourable option for children and teenagers as they provide a wide range of beneficial nutrients.
One study has shown that children consuming flavoured milk are not actually likely to have higher sugar or energy intakes as children consuming flavoured milk would likely, consume fewer less healthy sweetened drinks.
Flavoured milk is also less likely to cause damage to teeth than sugary foods and drinks.
Interestingly recent studies have suggested that chocolate flavoured milk can be used as an effective recovery aid after intense bouts of exercise.
Heat treated milks
Approximately 99% of milk sold in the UK is heat-treated, to kill harmful bacteria and to improve its shelf life.
Pasteurisation is the most popular method of heat treatment. It is a relatively mild form of treatment, which kills harmful bacteria without significantly affecting the nutritional value or taste of the milk.
The basic process for whole milk involves heating the milk to a temperature of no less than 71.7ºC for a minimum of 15 seconds (max 25 seconds). This process is known as High Temperature Short Time (HTST).
Following recommendations by The Advisory Committee on the Microbiological Safety of Food (ACMSF), which advises the UK Government Food Standards Agency, the UK dairy industry has extended the holding time for heat treatment of liquid milk to 25 seconds at 72°C. The purpose of this recommendation was to eliminate M. para tuberculosis (MAP) from milk.
After this the cold milk that enters the heat exchanger is heated by the hot milk leaving it, which in turn is partly cooled. Following heating, the milk is cooled rapidly to below 6ºC using chilled water on the opposite side of the plate. This process also extends the keeping quality of the milk.
Sterilised milk is available in whole, semi skimmed and skimmed varieties. It goes through a more severe form of heat treatment, which destroys nearly all the bacteria in it.
Firstly the milk is pre-heated to around 50oC, then homogenised, after which it is poured into glass bottles which are closed with an airtight seal.
There is no legally defined process for sterilising milk but, commonly, filled bottles are carried on a conveyor belt through a steam chamber where they are heated to a temperature of between 110-130ºC for approximately 10-30 minutes. Then they are cooled using a cold water tank, sprays or, in some cases, atmospheric air and then crated.
The sterilisation process results in a change of taste and colour and also slightly reduces the nutritional value of the milk, particularly the B group vitamins and vitamin C.
Unopened bottles or cartons of sterilised milk keep for approximately 6 months without the need for refrigeration. Once opened it must be treated as fresh milk and used within 5 days.
UHT or ultra heat treated milk is a form of milk that has been heated to a temperature of at least 135ºC in order to kill off any harmful micro-organisms (e.g. harmful bacteria) which may be present in the milk. The milk is then packaged into sterile containers.
All milk that is available for sale to consumers through supermarkets and milkmen must be pasteurised i.e. heated to 71.7ºC in order to make it safe for consumers and improve its shelf life. However UHT milks have a longer shelf life as a result of the higher temperatures to which they are heated and the packaging used to store them.
UHT milk is available in whole, semi skimmed and skimmed varieties.
Homogenisation of milk involves forcing the milk at high pressure through small holes. This breaks up the fat globules in order to spread them evenly throughout the milk and prevent separation of a cream layer.
This process basically results in milk of uniform composition or consistency and palatability without removing or adding any constituents. Homogenisation increases the whiteness of milk because the greater numbers of fat globules scatter the light more effectively.
Most milk available on the market is homogenised at present.