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.
How is milk 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, Scandanavia, 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 bourne 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 pasturisation and heat treatment techniques can be used in the production of milk which can affect storage capacity-detailed in later sections.
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.
Whole milk
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.
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
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
Organic milk comes from cows that have been grazed on pasture that has no chemical fertilisers, pesticides or agrochemicals used on it. Organic dairy herds diets must be made up of at least 60% grass so organic herds are truly free range and spend most of their time out in the fields. Organic dairy has higher welfare standards as well as being better for the wider environment.
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.
Organically produced milk contains higher levels of omega-3 polyunsaturated fatty acids, these are plant derived, short-chain fatty acids.
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
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).
The cold milk that enters the heat exchanger is heated by the hot milk leaving it, which in turn is partly cooled. After 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.
Homogenisation
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.
Untreated (raw) milk
All milk sold via the supermarkets and milkmen has to be heat-treated (pasteurised) to kill harmful bacteria. However, untreated milk can be bought direct form a limited number of farm distributors in England and Wales.
The farmer must hold a licence from DEFRA, the Department for Environment, Food and Rural affairs (formerly known as MAFF) to be able to sell this milk.
In 1999 the government introduced tighter controls on the production of milk when sold untreated, including more prominent and comprehensive labelling. Labels must indicate that the milk has not been heated above 40ºC. It must also carry the following warning: “This milk has not been heat treated and may therefore contain organisms harmful to health”.
The government prohibited sales of untreated milk through shops, hotels and other catering establishments in 1989. The sale of untreated milk in Scotland was banned in 1983.
Untreated milk represents less than 1% of the household milk market.
Filtered milks
Filtered milk goes through an extra, fine filtration system, which prevents souring bacteria from passing through.
The nutritional content of the milk is unaffected but the shelf life is increased.
The processes involved include, microfiltration, ultrafiltration and nanofiltration.
Microfiltration is the most commonly used process and is a pressure-activated separation process which uses a membrane that is permeable to substances with a low molecular weight but rejects material with a high molecular weight.
In the process of microfiltration of skimmed milk, bacteria are removed using ceramic filters with 1.4 micrometer holes to separate the milk from the bacteria. After this process, virtually all the bacteria present in the milk are removed.
The milk is then homogenised to standardise and evenly distribute the fat molecules, where it then undergoes the pasteurisation process before being chilled down quickly to 5ºC or less.
Microfiltration adds an extra level of cleanness which can extend shelf life up to 45 days when stored at temperatures of up to 7ºC and an average 7 days once opened.
Filtered milk is available in whole, semi skimmed or skimmed milk varieties
Homogenisation
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.
Information from the Dairy Council.
