Dairy farming: milk processing Case study – part 2

Learning objectives To recall the key stages in milk processing. To learn about primary milk processing.

Case study For three generations a family have farmed dairy cows and produced Cheddar Cheese in the West country. On this farm, each cow produces about 7,000 litres of milk per year, which in total supplies the cheese dairy with just over 7 million litres of fresh milk to be made into traditional farmhouse cheese. This volume of milk equates to an annual cheese production of 6,000 tonnes. Find out more http://www.foodafactoflife.org.uk/VideoActivity.aspx?siteId=19&sectionId=92&contentId=438

Primary milk processing After the milk has been delivery from the dairy, it is pasteurised. Pasteurisation is a process used to kill harmful microorganisms, such as certain pathogenic bacteria, yeasts and moulds, which may be present in the milk after initial collection. This process extends the shelf life of milk.

Pasteurisation The basic process for whole milk involves heating the milk to a temperature of no less than 71.7ºC for 25 seconds. This process is known as High Temperature Short Time (HTST). The milk is then cooled for packing, storage and transportation.

Homogenisation Homogenisation of milk involves the milk being pumped at very high pressures through narrow tubes, breaking up the fat globules in order for these to disperse through the liquid. This process produces milk of a uniform composition and palatability, without removing or adding any constituents. Most milk available for purchase is homogenised.

Packing The milk is then packaged into bottles and labelled. The packaging helps to increase the shelf-life of the milk. The milk is then distributed to supermarkets and shops for sale.

Other methods of heat treatment: Sterilisation This process uses a temperature in excess of 100ºC in order to destroy nearly all micro-organisms present in a food. This is important as some micro-organisms can form spores which have the ability to survive at high temperatures. The product is packed in air-tight containers either before or after heat treatment. Sterilising enables milk to be kept for 2-3 weeks unopened, but results in a burnt, caramelised flavour and browning.

Ultra heat treated (UHT) UHT is a continuous process and the product is packaged after treatment into sterile containers. Typical temperatures and times specified for UHT treatment of milk are 130º C – 150º C for 1-3 seconds. As the product is moving continuously, rather than being stationary, high temperatures can be reached resulting in fewer chemical changes, but having the same sterilising effect. UHT treatment was developed to destroy all micro-organisms without causing as much damage to the product as sterilisation. Milk may taste cooked and will be slightly brown in colour.

Find out more about milk To find out more about milk, access the From grass to glass – the journey of milk poster. Download the poster here: http://www.foodafactoflife.org.uk/attachments/4271d8ea-7f16-48353d1ff4a7.pdf

Quiz Take the quiz. Take the quiz End

Question 1 True or false? Pasteurisation is a process used to kill harmful microorganisms, such as certain pathogenic bacteria, yeasts and moulds, which may be found in the milk after initial collection. A. True B. False

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Question 2 What is homogenisation? A. Milk is heated and cooled very quickly to pasteurise the milk. B. Milk is pumped at high pressure to disperse the fat through the milk. C. Milk is sorted into different types according to fat content. D. The dairy cows are grouped according to milk yield.

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