Exam style questions

1. What is the natural sugar found in milk? (1 mark)

2. What enzyme does our body produced to break down lactose? (1mark)

3. What would be know as if we didn’t produce enough of this enzyme? (1 mark)

4. Explain the process of homogenisation and why it is done. (3 marks)

5. Explain the process of pasteurisation and why it is done. (3 marks)

6. What is meant by HTST? (1 mark)7. What is meant by the souring of milk? (2

marks)

Answers1. Lactose (1 mark)2. Lactase (1mark)3. Lactose intolerant (1 mark)4. Milk is forced through a small passage at high velocity. This

breaks down the fat globules in milk into much smaller ones and creates a stabile fat emulsion. Creates a distribution of fat, no cream layer on the top, gives a full-bodied flavour, gives a whiter, more appetising colour and increases the shelf life. (3 marks)

5. Milk is heated to a temp of no less than 71ºC for a minimum of 15 seconds. 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. (3 marks)

6. High Temperature Short Time? (1 mark)7. Bacteria present naturally in milk feed on the sugar (lactose) and

cause the milk to sour. It is a fermentation process. The lactose is converted to lactic acid which causes the pH to fall causing it to sour. (2 marks)

• 2 Dairy products • a) Characteristic, composition and factors affecting:• proteins in milk• caseins• whey proteins• lactalbumin• lactoglobulin• lactose content• b) Processes involved and reasons for:• milk processing• pasteurisation• homogenisation• sterilisation• c) The processes used to produce:• dried milk• evaporated and condensed milk• skimmed milk• cheese• butter• yogurt• ice cream• d) The characteristic changes in:• the souring of milk• mould attacks on cheese

Production of cheese

• Heat treatment of milk – it is pasteurised then cooled to 31oC and pumped into cheese vats.

• Addition of starter culture – starter is added to the milk to sour it (converts lactose into lactic acid). Lactic acid acts as a preservative and gives flavour.

Production of cheese

• Addition of rennet – rennet is from dried stomach of a calf. Contains rennin, an enzyme which causes milk to clot. Added 30mins after the starter.

• Cutting the curd – after 45mins a firm curd is formed. It is cut to release the whey.

• Scalding – curd is heated for 45mins when it is stirred by paddles.

Production of cheese

• Pitching – curds and whey are pumped into shallow coolers and the whey is run off from there once the curd has settled.

• Cheddaring – curd is passed into the cheddar master tower and left for 90mins. The curd drains. Creates silky texture.

• Milling – blocks of curd are milled to form small fragments ‘curd chips’

Production of cheese

• Salting – 2% salt added. Sprayed through fine jets. Flavour and preserves it.

• Pressing – gives texture and shape.• Wrapping – placed in polythene bags

under vacuum to exclude air and put into boxes.

• Maturing – cheese store to mature. Few days or several months. Temp between 5oC – 10oC.

Production of cheese

• Grading – which are mild, medium and mature.

• Packing – cut into retail size pieces. Range of packaging materials used.

Jimmy’s from the fridge 15.10-20.35

Cheese production

Food a fact of life - Food a fact of life

Write down the process as its discussed.

Moulds in cheese

• The moulds used in cheese production are common moulds that are widespread throughout nature.

• E.g. blue cheese production, enzymes eat away at the cheese, turning complex molecules into simpler ones. As a result, the structure of cheese is transformed into a more creamy-crumbly texture, and the sharp flavour and assertive aroma are created.

Moulds in cheese

• Most commonly used:

• Penicillium roqueforti, Penicillium glaucum and Penicillium camemberti.

• These moulds work to restrict the growth of harmful bacteria (Clostridium, Staphylococcus) within the cheeses they produce.

Yoghurt production

• Yoghurt is produced by the controlled fermentation of milk by two species of bacteria Lactobacillus sp. and Streptococcus sp.

• The sugar in milk (lactose) is fermented to acid (lactic acid) and it is this that causes the characteristic curd to form.

• The acid also restricts the growth of food poisoning bacteria and some spoilage bacteria. Yoghurt is safer and can be kept for up to ten days, under proper storage conditions.

Yoghurt production

• Fermenting milks with different micro-organisms has also provided an opportunity to develop a wide range of products with different flavours, textures, consistencies and, more recently, health attributes. These include:

• Live yogurts, which contain harmless bacteria that are added to the milk and are still present and alive.

• Probiotic yogurts, which contain live probiotic micro-organisms that are suggested to be beneficial to health.

• Bio yogurts, which are very popular and are made using bifidobacteria. Bio yogurt has a milder, creamier flavour which is less acidic than some other varieties and has shown to aid digestion and promote good health.

YouTube - How It's Made Yogurt 1min 25secs

Production of butter

1. Cream is heat treated, 2-4secs at 95oC2. Cooled to 4.5oC and maintained until for

several hrs to allow fat globules to harden.

3. A starter is added and temp is held at 15.5-18.5oC for 3-4hrs. Then cooled to 7oC

4. Churned at 4oC-fat globules form grains of butter

Production of butter

5. Buttermilk is drained off and then washed to remove any buttermilk.

6. Butter grains are worked for 10-15mins to form a solid mass. Salt maybe added or maybe left unsalted.

7. Butter can then be packed and graded.

Production of ice cream

• Dairy ice cream contains milk fat and non-dairy ice cream contains vegetable fat.

• Sweeteners, flavourings, emulsifiers and stabilisers are added during processing. Ice cream contains over 50% water from milk or other ingredients and air is incorporated into the product resulting in finely-distributed air cells protected by a layer of fat globules.

Production of ice cream

• The production of ice cream involves mixing the ingredients together, followed by pasteurisation; which reduces the number of non-pathogenic bacteria.

• After pasteurisation, homogenisation takes place. The mixture is left to age for 24 hours and during this time all the dry ingredients are hydrated and the fat is crystallised.

• The product is then frozen in a continuous freezer and air incorporation takes place. When the ice cream leaves the continuous freezer at -5ºC, approximately 50% of the water is frozen. The final process is hardening, which freezes out most of the water at -40ºC. Jimmy 20101219_1728

Exam style questions

• Give a detailed account of the effect of commercial processing on the palatability and nutritional value of cow’s milk. (8)

• Explain the functions of the following in the production of dairy products; (9)– Bacterial cultures– Enzymes– Acids

Exam style questions

• There is a wide variety of milk and milk products available to consumer groups. Suggest possible reasons for this. (8)