My studies showed me that once ancient man domesticated various livestock animals, he learned that the milk from the lactating mammal was tasty and highly nourishing. It wasn't long before he started to keep some of these animals specifically for their milk. Goats and cows were particularly important for this use, depending of course on the terrain. The goats would have been better in stony mountainous areas rather than cows, but where the vegetation was lush and the terrain flatter, the cow would provide more milk. Our islanders use a lot of milk, some goats' milk and much more cows' milk. The island has limited pasture land, so we import milk every year.

Once the milk was obtained from the animal, it had to be consumed quickly if it was preferred fresh. However, if an excess of milk was taken, it could not be stored in a fridge as we do today. Bacteria from the environment would gain access to the milk and start turning the milk sugar, lactose, into lactic acid, making the milk sour. With the milk becoming acid, the proteins in the milk would denature. Depending on which bacteria got to the milk first, yogurt or cheese of various flavours would be formed.

Bacteria are microorganisms usually visible only under a microscope. However, there are millions of them all around us, on surfaces, in air, water and soil and in animals and plants. Bacteria are single celled organisms that divide very rapidly in good growing conditions. Most bacteria are beneficial, but a few cause problems like disease and food spoilage. Bacteria that live beneficially with animals and plants live in symbiosis with their host. Some harmful bacteria produce toxins that make animals and plants sick - these are pathogens. Some harmful bacteria grow in our food and make it unpalatable, and even unsafe, to eat. Beneficial bacteria are used to provide new foods like cheese and yoghurt. Most of the beneficial bacteria are active in soil and water breaking down dead plant and animal material and releasing nutrients for recycling in the world.

Yogurt is formed when two particular strains of bacteria together form a symbiotic culture in fresh milk. They are Streptococcus thermophilus and Lactobacillus bulgaricus or L. acidophilus. The Streptococcus species starts to grow in the milk first. It produces methanoic acid and carbon dioxide.

These byproducts contribute to creating the ideal environment for the growth of the Lactobacillus species. L. bulgaricus releases peptides from the breakdown of milk proteins by proteolytic enzymes. The peptides in turn stimulate the growth of S. thermophilus.

The important chemical changes that take place are the conversion of the milk sugar lactose to lactic acid by L. bulgaricus and the formation of ethanol, which is a metabolic by-product produced by both bacteria. The lactic acid makes the milk proteins coagulate, causing the yogurt to thicken. The ethanol gives the raw yogurt its characteristic flavour.

The production of lactic acid results in a drop in pH of the milk. The pH of yogurt is about 4.2 - 4.4. This low or acidic pH prevents other harmful bacteria from colonizing the yogurt. Thus the goodness of the milk is preserved and can be consumed for some time after it is freshly produced at the dairy. It is argued that yogurt not only has the same nutritional value of milk, but that it is more easily digested.

Treatment of infections with antibiotics taken orally (by mouth) also kills important bacteria living in the digestive tract of the patient. This can lower the numbers of normal gut microorganisms and result in large numbers of antibiotic resistant bacteria. As a consequence patients get upset stomachs and even diarrhea. It also makes it difficult for doctors to treat patients with antibiotics, if their systems are filled with bacteria that are resistant to these medicines. To restore the normal gut microorganisms after treatment with oral antibiotics, doctors often recommend that patients eat yoghurt containing live bacterial cultures.

Requirements:
Fresh milk
Milk powder - optional, a thicker consistency will be achieved with the addition of milk powder
Small quantities of natural yogurt - note it must contain live cultures
A thermometer
Ice water if access to a fridge is limited
A thermos flask (or any other container that will help to keep the temperature constant)
A sieve

Procedure:

1. Measure an amount of milk into a container. (e.g. 2 cups)
2. Add 60-80g of milk powder if a thick yogurt is desired. Drinking yogurt will not require the addition of powdered milk. Sugar may also be added at this point.
3. Heat the milk to 85°C. If a thermometer is not available, heat the milk until a layer of foam begins to form on top of the milk. This step denatures the milk proteins and drives out dissolved air.
4. Quickly cool the milk to 40 - 45 °C in ice water.
5. Add about 1 teaspoon of live yogurt culture to 1 l of milk.
6. Use a clean spoon to stir the culture into the milk well to ensure it is evenly distributed
7. Pour the mixture into the flask and keep it at a constant 42°C. Leave for about 3 - 6 hours to thicken.
8. When the desired consistency and flavour is achieved, the yogurt can be cooled.
9. Sliced or chopped fruit, fruit pulp or more sugar may be added to the cooled yogurt to taste.

Answer the following questions:

1. Describe how you think yogurt production is an application of biotechnology.
2. What chemical changes must occur in milk before yogurt is produced? Which bacteria are responsible for each of these changes?
3. How does this chemical change contribute to the preservation of food?
4. Why do you think that the species name given to the Streptococcus species is thermophilus? Hint: break the word "thermophilus" down and look at the Greek meaning for each of the stem words.
5. Look at the following graph. It is applicable to yogurt production. Provide labels for the axes, the curves and a heading for the graph.

Cheese

Terms:

If a Streptococcus, Lactobacillus or Leuconostoc bacteria get to the milk first, cheese could be made. These bacteria will ferment the milk, causing lactose to be converted to lactic acid. The milk proteins will coagulate as a result of the increased acidity, causing then to curdle. The remaining watery liquid is known as the whey. The curds are drained of the whey and then compressed and aged to make a hard cheese.

In the olden days when it was difficult to control which bacteria would have access to the milk to ferment it into a cheese, a small amount of cheese was kept to start a new batch. Today there are known cultures that are specially bred and added to sterilized milk to make specific cheeses.

In this activity you are going to make cottage cheese. Cottage cheese is a very soft cheese. It is soft because it retains much of its whey and is only slightly drained. It is not aged at all so we will be able to make some on our own in the laboratory in a relatively short time. It will be a good idea to start this activity on a Monday so that the cheese can be enjoyed on the following Friday.

Requirements:

500ml of full cream milk
50ml of buttermilk
non-fat powdered milk (optional)
salt
herbs or gherkins or chopped chives or any other flavouring to taste
A double layer of muslin or cheesecloth (readily available at fabric shops) about 30cm square
A long length of string (1m will do)
Kitchen sieve
Thermometer
Bunsen burner and matches
Measuring equipment from the kitchen
A vessel in which to heat the milk over the flame
A mixing spoon

Procedure:

Monday

1. Wash your hands thoroughly because you will be working with food that you want to eat eventually. Also make sure that all the equipment you are going to use is very clean.
2. Pour the 500ml of full cream milk into a large beaker and heat to 37°C.
3. Stir in the buttermilk and mix well. At this point you may also add the powdered milk.
4. Cover the beaker with a cloth.
5. Incubate the mixture in a warm place (warm room temperature will do i.e. 25°C - 35°C) for 48 hours or until a firm curd has separated from the whey.

Wednesday

1. Make a double layer cloth, about 30cm square out of cheese cloth or muslin.
2. Line a kitchen sieve with the cloth and pour the curds and whey into the sieve.
3. Gather up the edges of the cloth to form a bag holding the curds. Use string to tie the top of the pouch closed. Hang the pouch where it can drain further. The bag will have to be refrigerated overnight.

Thursday

Open the bag and add flavouring of your choice. Re-tie the bag and let it hang overnight again.

Friday

Serve the cheese with crackers or bread. Share the cheeses amongst each other to try out all the different flavours.

Answer the following questions:

1. Explain why buttermilk is added to the plain milk to make cheese.
2. Why is it necessary to heat the milk?
3. Describe what takes place in the milk as it turns to cheese. You must refer to biochemistry and proteins to answer this question.

"One day, thousands of years ago, Xau was preparing to go out and track a herd of wildebeest in the hope of bringing home some fresh venison for his family. His mother was concerned about what he would find to eat, because all the maroelas were past their best and would give her son a stomachache.

The previous evening the goats had been milked and there was plenty of milk for everybody for the day. Xau's mother took a fresh calf stomach which had been cleaned for use as a container (remember, bottles had not been invented yet). She made sure that it was sealed with fine stitches of gut and filled it for milk for her son.

Xau set off early on his journey. He was a very pensive young man, always thinking about the philosophy of nature and could walk for hours appreciating his the Great Creation around him. He picked up the wildebeest spoor and started to visualize his hunt. The fresher the tracks became, the more excited Xau got and the more he focussed on the creature he would carry home to feed his family. He was so taken up with his hunt that he did not become hungry.

He found the herd, killed an old wildebeest bull, thanked it for giving its life to ensure the continuity of the lives of his family, heaved as much of the carcass as he could carry across his shoulders and retraced his steps home, glowing with pride.

On arrival home, Xau's mother was delighted with the meat he had acquired, but she was also pleased about the wonderful new stuff he had brought home in the calf-stomach carrier. It was a solid yellow substance in a liquid that she discarded. She compressed the hard solids into a block and served it with the meal. The first hard cheese dish ever to be served."

Cheese making is an ancient craft that was probably discovered by accident in a way similar to that outlined in the story above. It was used to preserve milk from attack by microorganisms that would make it unfit for human consumption. The soft cheese made in the activity above is a simple cheese. The harder yellow cheeses that are more popular in the making of a good toasted cheese sandwich require rennet in their production. Rennet is a mixture of chymosin and pepsin from a calf's stomach. Its role is to coagulate the main milk protein, casein. Rennet was traditionally extracted from the stomachs of unweaned calves, but recently geneticists have genetically altered a bacterium, which does the same thing as rennet, and this is added to the milk instead.

Today cheese making is an important industry with large-scale cheese makers throughout the country. The production of most cheeses involves the following steps:

The milk is heated to eliminate any microorganisms that may be present. This is to make sure that when the cheese is being made only selected bacterial strains will be present and the resulting cheese will be of a predictable quality.

Step 2 Milk coagulation

The coagulation is caused by the addition of the starter culture that consists of rennet and lactose-fermenting bacteria. The milk then forms curds and whey. Obviously Little Miss Muffet did not wait for her cheese to form when she sat down to eat her curds and whey.

Step 3 Curd extraction

The whey is discarded and the curds are retained.

Step 4 Salting, pressing

The curds are pressed to remove any remaining whey and bind the curd into a solid mass. Sometimes salt is added to the curds before they are pressed. The salt acts as a preservative and flavour enhancer. This raw cheese is then moulded into shape and coated with a layer of plastic or wax. This coating of the cheese prevents other wild microorganisms from colonizing the ripening cheese.

Step 5 Ripening

The cheese is stored under conditions appropriate for the type of cheese being made. The bacteria and any other microorganisms used specifically for that type of cheese continue to bring about chemical changes in the curd which improve and enhance the flavour of the cheese. The milk proteins are broken down into peptides enhancing the flavour and fats are also broken down into fatty acids. Thioesters are released during this process which give the cheeses their aromas.

Although bacteria are important microorganisms in the production of cheese, various fungi also sometimes play an important role. Camembert cheese has its surface sprayed with the spores of Penicillium camemberti and Roquefort or Blue cheese has Penicillium roqueforti inserted into its curd by special steel needles. The fungus on these cheeses gives them their characteristic flavours.

Look at the following label that has come off a cheese made in the Paarl area of the Western Cape:

Answer the following questions:

1. Draw a flow diagram to illustrate the manufacture of this cheese.
2. Which microorganism is responsible for the blue colour in the cheese?
3. What is Jersey milk?
4. Why do you think the manufacturer suggests the cheese be served at room temperature?

Win a PRIZE! (R100 book voucher from Exclusive Books, awarded monthly). E-mail your answers to this crossword puzzle to The Wizard. Click on the cool guy to send your e-mail. Go to the library, supermarket or to a local dairy to find some answers.

3 The thinning of the bones which leads to the loss of bone mass. Everybody loses bone mass with the natural process of aging, but when the loss of bone is so dramatic that even the slightest strain causes the bones to break, it is diagnosed as this disorder. By following a balanced calcium-rich diet, a healthy lifestyle and regular exercise, one can reduce one's chances of developing this disease.

5 The Indian name for butter from which the water has been driven off by heat.

6 A fine cotton fabric of very loose weave, originally used to press curds during the cheese making process.

10 A product in the cheese making process is the solid phase of the coagulum separated from the whey by cutting the coagulum. It consists of proteins, fat and some minerals and vitamins and will ultimately become the cheese.

11 The kind of milk that is left after the cream has been removed. It contains all the nutrients of milk with the exception of the fat and the vitamins associated with the fat.

12 The main protein in milk, from which it can be separated by the action of acid, the enzyme rennin, or bacteria. It is also the main component of cheese.

13 A yoghurt-like culture consisting of Lactobacillus acidophilus and any of the several species of Bifidobacteria. Health benefits claimed to be associated with the consumption of products containing this culture include the reduction in blood cholesterol, the alleviation of lactose intolerance, a strengthening of the immune system and a reduced risk of stomach and intestinal cancer.

14 The control of environmental conditions to prevent contamination.

15 The general term for anti-bacterial and anti-fungal substances produced by living organisms e.g. penicillium. The presence of these substances in milk is illegal.

1 The mechanical process by which milk is passed through a narrow opening at high pressure. The fat globules are broken up into smaller globules and evenly distributed throughout the milk. This will prevent the formation of a cream layer.

2 The process of milk thickening due to the presence of lactic acid and/or rennet. It is an important step in the cheese and yoghurt making process.

4 A colourless, almost odourless liquid produced by certain bacteria during the fermentation of lactose.

5 A rich, creamy frozen confectionery made commercially since the twentieth century from various milk products, sugar and fruit. It was made in China before 1000BC and was probably introduced to Europe by Marco Polo.

8 A type of bacteria which ferments lactose to propionic-acid, carbon dioxide and other products. These bacteria are used in the manufacturing of Emmenthal cheese where they are responsible for the formation of eyes and contribute to the characteristic sweet flavour.

9 Holes produced by propionic bacteris due to propionic acid fermentation of acid, carbon dioxide and other products.

Bread baking has been around since before the 20th century BC. The bread leavening and baking process was probably discovered by accident in Egypt where archeologists have found pieces of leavened bread in deposits dating back to the year 3 500 BC.My uncle Tshepo has a bakery on our island. I asked him for his recipe so that I could make bread that reminds me of home when I get homesick. This is the recipe he gave me:

Flour           100 parts
Salt            1 part
Sugar           1 part
Yeast           5 parts
Vitamin C       0,5 parts
Milk or water   60 parts

Because Uncle Tshepo bakes between 1000 and 1200 loaves of bread per day, his recipe does not give fixed amounts.

Convert the above recipe into one where 3 cups of flour will be used. Remember that 1 cup equals 250ml.

Uncle Tshepo told me that all the ingredients in the recipe play a very important roll in production of a loaf of bread. If any ingredient is left out, the bread will flop. Let us look at what roll each of the ingredients plays:

Flour:

Bread is mostly made using wheat flour which contains several proteins, collectively known as glutens. It is the glutens in the flour that give the bread dough the elasticity required creating the spongy, light texture characteristic of bread. The dough must be elastic enough to hold the carbon dioxide bubbles created by the yeast. The gluten, when hydrated undergoes chemical changes that make the dough elasticFlour made from any other grain does not contain as much gluten.

The flour is also a rich source of carbohydrate and it is for this reason that bread is a staple in many diets throughout the world. We eat bread for the energy we derive from it.

Salt:

Develops flavour and toughens the gluten so that the dough will be less sticky. Because it slows down the rate of fermentation, it is sometimes added after the fermentation process.

Sugar:

The primary function of the sugar is to provide a substrate for the yeast. The yeast feeds on the sugar causing the fermentation that is required for the dough to rise.

Yeast:

The yeast is a block of single cell organisms whose job it is to change the sticky dough of dry ingredients and liquid into the light and spongy mixture which is baked to create bread.

After mixing all the ingredients, the yeast feeds on the sugar, breaking it down into ethanol and carbon dioxide. The carbon dioxide is trapped in the elastic matrix formed by the dough, causing the dough to increase in volume. This is called leavening or rising.

Vitamin C:

This helps to make the dough more elastic, resulting in less time required for leavening.

Milk or water:

The liquid component of the recipe binds all the dry ingredients and hydrates the glutens in the flour.

Other ingredients may be added to the basic recipe to alter the flavour, nutritional content and shelf life of the loaf.

Non-fat milk powder can be added to improve the flavour and nutritional value. Fats such as butter or oil makes the dough easier to handle, improves the texture of the crumb, increases the shelf life and in some cases enhances flavour.

Eggs add flavour and colour as well as making the dough easier to handle. They also make the crumb softer.

Other commercial ingredients may be added such as dough improvers to adjust handling properties, yeast foods to enhance leavening, mould inhibitors to increase shelf life and vitamins and minerals to increase the food value of the bread.

The following information was found on a loaf of bread purchased at a supermarket in Boksburg.

Question:

By considering the nutritional information given above, discuss this statement: 'Bread is a staple food mainly in countries where wheat is grown.'

The baking process

The following scheme applies to all conventional bread production:

It is important during this step to make sure that ingredients are put together in the correct proportions. If too little or too much of a single ingredient is added, the bread will be a culinary flop.

When mixing the dry and wet ingredients, the glutens in the flour become hydrated. These proteins undergo physical and chemical changes allowing them to coalesce into gluten fibrils that give the dough its silky, elastic characteristics. The kneading process also helps to create nuclei for gas production and the expansion of the dough.

It is now that the yeast must perform its important task. It feeds on the sugar breaking it down to ethanol and carbon dioxide. Enzymes in the yeast cells catalyze this fermentation process. The carbon dioxide bubbles are trapped in the dough, causing the volume of the dough to increase (the dough rises).

The yeast also contains proteolyic enzymes that act on the glutens, making them less tough and stringy. Overall, the leavening process leads to tastier, lighter dough that is more easily digested.

The dough is kneaded to release the bubbles that are too large. Too large bubbles will spoil the texture of the bread and will lead to slices with big holes in them.

The dough is cut into loaf size pieces and placed in loaf pans. In industry this is referred to as the make-up stage.

The yeast is asked to do it job once again to ensure the correct spongy texture of the loaf.

The loaves are baked and it is during this process that the yeast cells are killed off, the ethanol is evaporated and the flour and other ingredients are cooked.

Any enzymatic reactions are also stopped.

Follow the recipe, trying to see the science involved in the process, and answer the questions associated with each step.

Ingredients:

Questions:

Step 1:

Start the action of the yeast (before combining any of the other ingredients) by softening the yeast in lukewarm water with 1 teaspoon of sugar for 10 minutes. Both the compressed yeast and the fast granular yeast should be treated in this way. The compressed yeast should be crumbled, whereas the granular yeast may be added directly from the package.

Questions:

Step 2:

Scald the milk. The purpose of scalding is to destroy enzymes in the milk, thus protecting both the yeast and the dough.

Questions:

Step 3:

The scalded milk, salt and ¼ cup of sugar is then put into a large mixing bowl and cooled until lukewarm. (If half water is used, this may be added lukewarm to the scalded milk to hasten cooling).

Questions:

Step 4:

Stir yeast mixture into lukewarm liquid. If the yeast is overheated at any time, it will be injured or even destroyed; if it is too cold, it will act very slowly.

The ideal temperature for the rising of yeast bread is an even warmth of about 84°F, which is a little less than body temperature.

Step 5:

Add about half the sifted flour (4 cups) and beat until smooth.

Questions:

Step 6:

Beat in the cooled melted shortening.

Step 7:

Add enough flour to make a smooth soft dough. The softer the dough can be kept without sticking to either the board or hands, the lighter and more tender the bread will be when baked.

Step 8:

Sprinkle the breadboard very lightly with 1 to 2 tablespoons of flour and rub evenly over the surface. (The flour on the board will be part of the sifted flour measured for the bread, since most of it will be kneaded into the dough).

Questions:

Step 9:

Turn the dough onto the floured board, cover and let rest for 10 minutes before kneading. As can be seen in the drawing, the dough is very soft as it is turned from the bowl. Allowing it to rest will cause it to stiffen and be easier to handle without adding an excess of flour.

Step 10:

Now knead the dough until the outside is smooth and elastic, for 10-15 minutes. There are 3 basic motions to kneading: folding the dough over on itself towards you, pushing the dough with the heel of the hands away from you, and then making a quarter of a turn and repeating the process. The drawing illustrates the first motion of folding the dough towards you.

Questions:

Step 11:

Then in an easy rhythm the motion of the hands rocks back to the heel of the palm and the dough is pressed and pushed out away from you. This kneading of the dough develops the bread protein (gluten) and provides an elastic structure that will be strong enough to hold the expanded gas produced by the yeast, and will hold the shape of the loaf when it is baked.

Questions:

Step 12:

By lifting up the edge of the dough and turning it with the left hand, and at the same time folding the dough over with the right, you will again be in position to repeat the kneading process starting with step No. 10. This process may be somewhat awkward at first, but with practice both hands may be used to advantage, and an easy, rhythmic, continuous motion developed. The dough should feel satiny and smooth, and should stick to neither the board nor the hands.

Questions:

Step 13:

Round up dough into a smooth ball and place in a well-greased clean mixing bowl large enough to let it double in bulk without overflowing. To prevent the formation of a thin crust on top, which will make streaks in the dough and bread, turn the ball of dough over in the grease bowl to coat the entire surface with fat before setting to rise.

Questions:

Step 14:

Cover the bowl with waxed paper and a towel, lid, or a second bowl of the same size, and place in a warm spot away from draughts to rise until fully doubled in bulk; 86°F is the best temperature for this rising. If the room is too cool, the bowl of the dough may be set in a cupboard with a pan of hot water beside it.

Questions:

Step 15:

The dough should not be hurried through this first rising. Allow enough time for it to fully double its bulk (from 1 ½ to 2 hours). When the dough is light enough, there will be gas bubbles visible just below the surface of the dough and the dent made by pressing your finger into the dough will remain and not spring back.

Questions:

Step 16:

When the dough has risen fully, punch down by plunging your fist into the centre and folding the entire edge towards the centre and punching down again. Then turn the dough over so that the smooth side is up, cover and allow to rise again until double in bulk. The second rising will take less time than the first. A single rising will produce a very satisfactory loaf, but for a very superior loaf a second rising is recommended. After each rising, punch down and turn out on a lightly floured board.

Step 17:

Divide into 3 equal portions, and round up into balls.

Questions:

Step 18:

Cover with bowls, and let dough rest for 10 minutes, then shape into loaves. This 'rest period' keeps the dough from springing back as it is shaped into loaves or rolls, and makes it much easier to handle because the protein is relaxed.

Step 19:

Place loaves in greased bread pans, cover and let rise again until doubled in bulk, about 1 hour, in a warm place (86°F).

Questions:

Step 20:

Bake in a moderately hot oven (400°F) for 15 minutes, then reduce heat to 375°F and bake for 35 minutes longer for loaves of this size. Bread when done should be well risen, with a fully rounded top ("spring"). The loaves should sound hollow when tapped on the bottom.

Questions:

Step 21:

Turn loaves out and cool thoroughly for at least 3 to 4 hours, uncovered, and away from draughts before slicing. If cooled too quickly, the crust will shrivel, become bumpy and soft.

Genetic scientists are looking for ways to produce better strains of yeasts to be used in baking. They want to produce strains that provide better flavour and that make the dough rise in less time and at lower temperatures.

Questions

1. What benefits would a commercial baker derive from creating a strain that makes bread rise faster and at lower temperatures?
2. What other improvements could you suggest the genetic scientists look at?