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Soya yoghurt is a product not yet available commercially. If incorrect cultures are used for the manufacture of the yoghurt, a vile tasting product is prepared. Special strains of Lactobacillus acidophilus which utilises raffinose and stachyose present in soya beans, instead of lactose must be used. Two cultures are used for the preparation of this product, one for flavour and the other for the production of acid.
Soya milk is used for the manufacture of soya yoghurt
Mixing with other ingredients
The soya milk is mixed with whey solids ( 1part whey solids:50 parts soy bean milk), and sucrose ( 2,5 parts sucrose : 50 parts soy bean milk). The sucrose is added to promote the taste of the final product. The whey is added to increase the firmness of the product.
Heating is the imparting or generation of heat to a product
Heated to boiling point (90-100°C) in a vat which is heated indirectly. The vat are jacketed vessel used for heating and cooling for small-medium scale processors. The tanks are insulated to ensure that an even temperature is maintained during processing. Cone-shape tanks will ease the removal of the product
Mixing with adjuncts
A 20% gelatin solution which has been sterilized at 121°C for 10 minutes is prepared for addition to the heated mixture. A 1% solution (2,4 parts of 20% solution : 50 parts soy mixture) .
Cooling involves extracting heat from the product to decrease it temperature using an appropriate device such as a heat exchanger and medium, e g water, air or refrigerant
Cooled to (50-80°C) by stirring the mixture or by pumping cold water in the double sided vat. The vat are jacketed vessel used for heating and cooling for small-medium scale processors. The tanks are insulated to ensure that an even temperature is maintained during processing. Cone-shape tanks will ease the removal of the product
Fermentation is the conversion of organic substances to simpler substances by the action of enzymes or living organisms such as bacteria or microorganisms, including yeasts, moulds and fungi.. Fermentation changes the quality of the products and some food products are more edible after fermentation, more nutritious and more flavourful.
Fermentation takes place in fermentation tanks (large scale ) and in the jacketed vessel used for heating and cooling for small-medium scale processors. The tanks are insulated to ensure that an even temperature is maintained during the incubation. Cone-shape tanks will ease the removal of the coagulum
The product is pumped into the fermentation tanks and inoculated with a 2% culture of a mixture of Lactobacillus acidophilus B-1910 1and Lactobacillus acidophilus B-2092 1. The product and starter culture mixture is agitated to ensure even dispersion of the culture in the product. The product is incubated for 20-24 h at 37-40°C.
Cooling involves extracting heat from a food product to decrease its temperature using an appropriated device such as a heat exchanger and medium, eg water, air or refrigerant.
The fermented product is cooled to 15°C. This is done to retard further acid development. Tubular or plate heat exchangers are used for large scale producers and small and medium scale processors will pump water into the jacket of the vessel to cool the contents.
The plate cooler is similar to the plate heat exchanger. It is compact, simple and easily cleaned. It consists of series of stainless steel plates mounted vertically supported by cylindrical bars and tightly packed and sealed together. The plates have waffle-like indentations which provide a large heat transfer area and a turbulent flow of the liquids. A rubber-seal between the plates keep them about 16-18mm apart to minimise the risk of structural damage to the coagulum. The liquids leave the plates through holes in the corners of the plates. Open and blind holes route the liquids to the correct plate processing area. Chilled water is used to cool the coagulum indirectly.
Tubular coolers is made up of a bundle of tubes enclosed in a container. The coagulum passes through the pipes and a counter-flow of cooling agent passes around them.
The yoghurt can then be kept in storage under controlled conditions for 10-20°C
The cooled product is gently stirred with minimal shear to the product. Positive displacement pumps and short lengths of wide diameter pipelines are used for large scale processors
There are three different kinds of positive displacement pumps 1) Pumps with reciprocating displacers which is a low-pressure piston pump and is often used in the filling machines. Damage to yoghurt is minimised by a short contact time between the pump and the yoghurt, low temperature of operation (10-15°C) and no back pressure. 2) Rotating displacement pumps where the product moves through a rotating cavity between two rotors. The yoghurt enters the pump by gravity and a portion of the yoghurt is trapped between the lobes and the pump casing and is then gently transferred to the other side of the pump. The advantages of the rotating displacement pump : can work at a high speed, suitable for pumping viscous products. 3) Screw pump: Used especially for fruit yoghurt. A single helical rotor/screw turns within a static stator. The yoghurt travels along a continuous spiral without a change in volume, the yoghurt is treated gently.
Small and medium processors will stir the yoghurt in the vat. The vat are jacketed vessel used for heating and cooling for small-medium scale processors. The tanks are insulated to ensure that an even temperature is maintained during processing. Cone-shape tanks will ease the removal of the product
Fruit and flavour addition (optional)
Blending is a means of dispensing additional components or ingredients into an existing food system, uniform distribution of ingredients/components
Pasteurised fruit is added in. In line mixers with a gentle stirring action are used to disperse the fruit evenly throughout the yoghurt. The requirements set by the legislation must be met and adhered to.
The fruit can be manually added to the yoghurt in the vessel (batch blending). Continuous blending consists of three units, namely the metering device to ensure the correct amount of fruit per volume yoghurt added and a metering device for the yoghurt and a mixing chamber to ensure uniform distribution of the fruit.
Filling and Sealing
Filling involves displacing the air in the container with a food product prior to sealing
Sealing is the closing of a packaging material to ensure that the food stays enclosed and uncontaminated.
The containers (bottles/cans) are filled, by the injection of the mixture into the containers with nozzles. Small and medium scale processors will hand fill and seal the containers. The containers are hermetically sealed. A hermetically sealed container is an unopened containers which cannot be opened without breaking or damaging the container, seal, adhesive tape or any other attachment which may protect the contents against the entry of micro-organisms. The product must be stored at temperatures between 4-5°C.
Products must be correctly labelled according to the requirements set out in the Labelling and Advertising Regulations R2034/1993
1 South Africa - Foodstuffs, Cosmetics and Disinfectants Act (No 54 of 1972) and regulations:
1.1 Fats and Oils:
R1316/1996 Edible fats and oils
R965/1977 Preservatives and antioxidants
R2507/1982 Anticaking agents
R115/1986 Acids, Bases and salts
R2527/1987 Emulsifiers, Stabilisers and Thickeners
1.3 Maximum levels of residues
R1809/1992 Maximum levels of residues of veterinary medicines and stock remedies
R246/1994 Maximum levels of pesticide residues
R1518/1994 Maximum levels of metals in food
R1183/1990 Perishable foodstuffs
R2034/1993 Labelling and advertising
R692/1997 Microbiological Standards
2 South Africa - Health Act (No 63 of 1977) and regulations
R1128/1991 Inspections and investigations
???R2261/1991 Food premises and the transport of food
3 South Africa - Agricultural Products Standards Act (No 119 of 1990) and regulations
4 South Africa - Perishable Export Control Act (No 9 of 1983) and regulations
5 South Africa - Occupational Health and Safety Act (No 85 of 1993) and regulations
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