WINE
After the grapes, which acquire natural yeasts during growth, are harvested the juice is extracted in presses. Solid matter, such as the seed and stems, are taken out in a high speed, rotating centrifuge. Sometimes the juice or ‘must’ is heated gently to kill unwanted microorganisms. Alternatively, sulphite – derived from sulphurous acid – is added to control the microorganisms. The must ferments naturally, due to the biological activity of the natural yeast of the grapes. They convert the natural sugar in the grape juice into alcohol.
Red wine, made from black grapes, is fermented at 21- 29 C for about two weeks. Its colour derives from the skin pigment, anthocyanin. White wine is fermented at 10- 15 C for three to six weeks. Cooler temperatures need longer periods for adequate fermentation. Red wine, being more complex, requires higher temperature fermentation.
Afterwards, the wine is filtered to remove sediment, then stored and later bottled. Most wine is now stored initially in large steel tanks. It may be matured for one or many years, during which important flavour changes occur.
BEER
Barley is the major raw material for beer, of which 15.5 thousand million gallons are drunk every year. To turn barley into beer, harvested barley grains are moistened with water and allowed to germinate until they sprout. Sprouted barley is called malt, and it dried for use later.
Most modern breweries buy prepared malt. They soak it in warm water, in what is called the ‘mashing’ process, and then extract liquid, which is called wort. The liquid wort is boiled with hops that give the characteristic flavour of beer. It is then cooled and selected strains of yeast are added. Like most plants, yeast grows faster at warm temperatures. Lower temperatures of 10-15 C are used for lager, with a fermentation time of 8 to 10 days. Lager yeast requires a cooler temperature in which to grow.
At the end of fermentation, the beer is filtered or spun in a cylinder called a centrifuge, which removes the yeast cells. It may be pasteurised by heating to give it a longer life, and is often casked, bottled or canned and aged before being drunk. Beer contains 85 to 93% of water. It may also contain a small percentage of sugar, between 2 and 10% alcohol, and some minerals and b vitamins.
BREAD
One of the ingredients of bread is yeast. After the dough has been kneaded, it is put in a warm place. The yeast respires with oxygen by feeding on the sugars and breaking them down into carbon dioxide and water. These gases cause the dough to rise. As you bake the dough, the yeast is killed, and the gases expand to give the bread a spongy texture. If dough without yeast is used, it will not rise. The bread it makes is called unleavened bread.
DAIRY PRODUCTS
Milk is a watery solution of protein, sugar, vitamins and minerals with fat droplets to make the milk white. But it also contains bacteria that feed, breed, and make the milk sour in a few days. Our ancestors discovered that they could preserve the nutrients in the milk by turning it into cheese and yoghurt.
CHEESE
After cows are milked, a tanker transports their milk to the dairy. The milk is heated the pasteurise it, killing harmful bacteria. Next, special bacteria are added to the milk, they feed on lactose (milk sugar), making lactic acid in the process. The acid thickens the milk and makes it turn sour. The milk is warmed and rennet, which comes from calves’ stomachs, is added. Rennet contains an enzyme called rennin that makes part of the milk thicken into solid lumps. The solid lumps are called curds. They are cut to help the watery part of the milk (whey) drain away. The whey is made into food for farm animals. Salt is added to the curds, and they are pressed to remove any remaining whey. The curds are shaped into moulds and stored on cool shelves and left to ripen into cheese.
YOGHURT
Adding certain bacteria (lactobacilli) to milk and allowing this to ferment without oxygen makes yoghurt. The bacteria multiply and cause the milk to thicken. They reduce the sugar content by converting the milk to sugar, lactose, into lactic acid (similar to cheese production). This is why natural yoghurt tastes sour.
OTHER FOODS
Enzymes are also used in the production of many other foods. In meat, they are used to make it tender. In confectionery enzymes are used to break down starch syrup into glucose syrup (carbohydrases are used) or change glucose into fructose which is sweeter so less is needed and is used in slimming foods (insomerase) or break down sucrose into glucose and fructose or lastly, to make artificial sweeteners. Enzymes are also useful in baby food as they start off the digestion process of proteases and lipases. Enzymes also have other uses including medical treatments for cancer and penicillin as well as biological washing powders. These breakdown stains (proteases attack proteins and lipases attack fats) and also to soften fabrics (cellulases break down the ‘bobbly’ bit that can form.
