Agro-processing of dairy

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One of the many opportunities available to farmers to grow their markets, turnover and profits is by adding value to farm produce through further processing. Two types of processing methods normally apply to raw materials, primary processing and secondary processing.

Milk is one of the most versatile products available to the processor. Processing options include fermentation, concentration, freezing and several other preservation methods. Processed dairy products are divided into five groups:

Concentrated dairy products

Butter – continuous process

Butter is a dairy fat spread that contains at least 80% fat by weight and less than 16% moisture. Butter can either be made from sweet (uncultured) or sour (cultured) cream. The process makes use of a continuous butter-making machine (churner) with capacities ranging from 12kg per hour to 10 tons per hour.

Butter oil – direct process

Butter oil consists of more or less pure milk fat in liquid form, generally containing between 99,3 and 99,8% milk fat. Butter oil is convenient for mixing and metering into other products such as chocolate, ice cream and various confectionery products.

Pasteurised cream

Pasteurised cream is a high-fat fluid dairy product that has undergone mild heat treatment to inactivate pathogenic micro-organisms and to improve the keeping quality of the product. The fat content of the product is adjusted so that it corresponds to a specific product category as prescribed by legislation, for example the terms ‘whipping’, ‘whipped’, ‘dessert’ and ‘coffee cream’.

Evaporated milk.

Evaporated milk

Evaporated milk is a concentrated, sterilised product with a light colour and an appearance similar to that of cream. It is used as a replacement for fresh milk for cooking, coffee creaming and even baby feeding (when fortified).

Cultured dairy products

Amazi

Amazi is cultured (sour) milk that is manufactured by inoculating pasteurised milk with a specific bacterial culture. The finished product has a firm texture, no gas bubbles and no separation of whey from the coagulum.

Cultured buttermilk

Cultured buttermilk is the product obtained from buttermilk that has been inoculated with a starter culture to produce a viscous liquid with a mild lactic flavour.

Yoghurt.

Stirred yoghurt

Stirred yoghurt is a fermented milk product with a thick, smooth consistency and may or may not be flavoured. It is incubated in tanks, stirred, flavoured and cooled before packaging.

Gouda cheese

Gouda is a close-textured, mild cheese. It is classified as a semi-hard cheese.

Cheese spread

Cheese spread is a blend of hard cheese with added emulsifying salts. The mixture undergoes a heat treatment that increases its shelf life. Cheese spread has a relatively high moisture content (± 55%) and a pH of 5,7 to 6,3.

Sour cream

Cultured (sour) cream is the product obtained from cream that has been inoculated with a starter culture to allow for the development of lactic acid and flavour compounds under controlled conditions.

Kefir

Kefir is a smooth, viscous, fermented dairy drink with a fresh acidic taste and contains lactic acid, alcohol (±1%) and gas (carbon dioxide).

Kefir.

Frozen dairy products

Frozen yoghurt

Frozen yoghurt resembles ice cream and is prepared by freezing an aerated mixture of yoghurt.

Liquid dairy products

Pasteurised milk

Pasteurised milk is milk that has undergone a mild heat treatment to inactivate pathogenic micro-organisms and to improve the keeping quality of the product. The fat content of the product is adjusted to create different product categories that suit the legal classification of milk based on its contents.

Sterilised milk

Sterilised milk is milk that has been subjected to a special heat treatment to extend the shelf life. The milk is heat treated in the final retail container (glass or thermo-stable plastic bottles). The sterilised milk will remain fit for consumption for several months if stored at ambient temperatures. The milk has a characteristic cooked flavour and rich texture. Flavoured and coloured products are also available.

Powdered dairy products

Acid casein

Acid casein is the product obtained by coagulating milk with acid. This provides a much more effective way of preparing caseinate solutions. Acid casein is mainly used for paper coatings and adhesives.

Rennet casein

Rennet casein is the by-product obtained by coagulating milk by means of rennet. It is fairly insoluble, but it can be dissolved using polyphosphates and it is then used to manufacture cheese analogues. Rennet casein can also be used in the manufacturing of plastics, especially blanks for button manufacturing, and in the manufacturing of artificial horn and ivory.

Roller-dried caseinate

Caseinate powder (roller dried) is produced from fresh (wet) or dry casein curd that has been dissolved in a diluted alkali solution and dehydrated by means of roller drying. It is extensively used as an emulsifier in processed meat products or as a milk substitute.

Milk powder.

Spray-dried caseinates

Caseinate powder (spray dried) is produced from fresh (wet) or dry casein curd that has been dissolved in a diluted alkali solution and dehydrated by means of spray drying. It is extensively used as an emulsifier in processed meat products or as a milk substitute.

Cheese powder

Cheese powder is the product obtained by the removal of the water fraction from cheese, with or without food additives. Cheese powder is usually manufactured from cheddar cheese. Cheese powder is utilised in the flavouring of snacks, where it is used to coat or mix the product.

Ice cream powder

Ice cream powder is prepared by dehydrating a pasteurised ice cream mix. The powder is sold to retailers to prepare soft-serve ice cream using a special in-store freezer.

Roller-dried milk powder

Milk is dehydrated on hot rollers. Roller-dried milk has some specialised applications, e.g. for chocolate manufacturing.

Spray-dried milk powder

Milk powder is manufactured by dehydrating pasteurised, concentrated (evaporated) milk by means of a spray-drying process.

Whey powder

Whey is the watery residue of cheese and casein production. Powdered whey can be used for animal feed, milk substitute and as an ingredient in the baking industry.

Further processing options

The products discussed above are only a small sample of the many processing methods and products available to the dairy processor. Other options range from products such as condensed milk and set dairy dessert to ricotta.

The manual on the agro-processing of dairy contains complete information on the products discussed above, as well as many other processing methods and products available to the dairy processor. It is available from the ARC – Institute for Agricultural Engineering. Contact Elmarie Stoltz on 012 842 4017 or stoltze@arc.agric.za.

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