This inhibits the growth of spoilage microbes. Consequently yoghurt keeps well in the fridge for some days. The presence of lactic acid causes the structure of the milk protein to change, this gives Yoghurt its special thickened texture. The lactic acid also gives the yoghurt its sharp taste. Other products of the lactic acid fermentation such as acetaldehyde give the yoghurt its characteristic smell.
Cheese-Making
The basic principle involved in making all natural cheese is to coagulate or curdle the milk so that it forms into curds and whey. Curdling is done by the addition of a starter (a bacterial culture which produces lactic acid) and rennet the coagulating enzyme which speeds the separation of liquids (whey) and solids (curds). There are two basic categories of starter cultures. Generally, cheesemaking starts with acidification. This is the lowering of the pH (increasing acid content) of the milk, making it more acidic. Classically, this process is performed by bacteria. Bacteria feed on the lactose in milk and produce lactic acid as a waste product.
After acidification, coagulation begins. Coagulation is converting milk into curds and whey. As the pH of the milk changes, the structural nature of the proteins changes, leading to curd formation. Essentially, the proteins in the milk form a curd that entraps fat and water. Although acid alone is capable of causing coagulation, the most common method is enzyme coagulation. The physical properties of enzyme-coagulated milk are better than that coagulated purely with acid. The traditional source of enzyme is rennet.
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After the coagulation sets the curd, the curd is cut. This step is usually accompanied with heating the curd. Cutting the curd allows whey to escape, while heating increases the rate at which the curd contracts and squeezes out the whey. The purpose of this stage of the process is to make a hard curd. Many surface ripened cheeses have their surfaces smeared with a bacterial broth. With others the bacteria is in the atmosphere of the curing chambers. These cheeses are called washed rind varieties as they must be washed regularly during their ripening period (longer than for Camembert or Brie) to prevent their interiors drying out. The washings also help promote an even bacterial growth across the surfaces of the cheeses. As this washing can be done with liquids as diverse as salt water and brandy, it also plays a part in the final flavor of the cheese. The ripening occurs.
Beer-Making
The first step is, called malting, involves steeping the grain in water for several days until it begins to germinate. During germination, enzymes within the grain convert the hard, starchy interior of the grain to a type of sugar called . At this point, the grain is called . After several days, when the majority of the starch has been converted to sugar, the malt is heated and dried. This process, called kilning, stops the malt from germinating any further. After kilning, the dried malt is processed in a mill, which cracks the husks cracked malt is transferred to a container called a tun, and hot water is added. The malt steeps in the liquid, usually for one to two hours. This process, called mashing, breaks down the complex sugars in the grain and releases them in the water, producing a sweet liquid called wort. The temperature and amount of time used to mash the malt affects the body and flavor of the finished beer.
In the next step, called brewing, the wort is transferred to a large brew kettle and boiled for up to two hours. Boiling effectively sterilizes the wort to kill any bacteria that may spoil the wort during fermentation. During this stage of the brewing process, hops are added to the wort to provide a flavor and bitterness that balances the sweetness of the wort. After brewing, the wort is cooled and then strained to remove the hop leaves and other residue. The brewer transfers the wort to a container in which it can ferment. Yeast is then added or pitched into the wort to begin fermentation. When the yeast has consumed most of the fermentable sugar, the wort becomes beer.The beer is transferred to an airtight container, called a conditioning tank, for a second fermentation.
Wine-Making
Grapes are firstly crushed. The crushed grapes and juice are called must. What happens next depends on the type of grape. Red-grape must is sent directly to the fermentation tanks. White-grape must is sent first to a wine press, where the juice is separated from the skins, because white wines are fermented from skinless grapes.The must, whether from red grapes or pressed white grapes, is ultimately sent to the fermentation tanks. These tanks are airtight. The tanks are cooled with glycol to maintain a temperature. The winemaker adds sugar and yeast to start the process of fermentation. The type of yeast and the amount of sugar added depends on the type of grape. Once the fermentation process is completed, red wines are sent to the press to separate the skins from the wine.. Once the yeasts are removed, the wines are stored in either stainless steel storage tanks or oak barrels. In some red wines, a second type of fermentation, called malolactic fermentation, is undertaken while in storage. In malolactic fermentation, the winemaker adds a bacteria to the wine that breaks down malic acid, a byproduct of aerobic (oxygen-requiring) metabolism, into lactic acid, a byproduct of anaerobic (no oxygen) metabolism. Lactic acid is a milder acid than malic acid. The aging process can be anywhere from three months to three years.
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