Dairy pertains to milk and its derivitives. Milk is an opaque white fluid secreted by female mammals. Intended as the sole sustenance for newly born offspring it is very nutritious. "Milk", without qualification, generally denotes cow's milk. However the milk of many other mammals is also a source of human food.
A complex structure, milk is an emulsion, suspension and solution of fat globules, protein, salts, sugar and vitamins in water. While most milks contain the same substances, they vary in their proportions from species to species, and within the same species, according to breed.
When fresh milk stands, the fat globules, being too large to remain in suspension and lighter than water, eventually rise to the top, formimg a rich layer called cream. Creaming, the separation of milk fat, is now usually achieved by centrifuge.
By its nature raw milk is hospitable to microbes and is readily tainted. Many milk-based products derive from measures to control this susceptibility and exploit it to advantage. Thus the conversion by certain bacteria of lactose to lactic acid give rise to yoghurt and sour cream. Nowadays, routine pasteurization, the combination of high temperature and time, destroys most of the microbes, both harmful and beneficial, in raw milk.
Much milk is also homogenized, a treatment forcing milk through tiny holes. Broken thereby into smaller globules, the fat is distributed through the milk and cannot "cream".
Cheese is, essentially, a mass of solids extracted from curdled milk. It is, however, phenomenally diverse in character, the result of the many variations in the extraction process. Cheeses range in taste from mild to strong, in aroma from imperceptible to pungent, in texture from soft to hard, in colour from white to yellow to blue, in size from tiny to huge, in fat content from low to high, and in age from fresh to mature, all with nuances in-between.
Because of the many variables, there is no single standard cheese-making method; nevertheless, all cheeses have certain processes in common. First the milk is soured, and thereby separated into curds (solids) and whey (liquid). Next the solids are concentrated: a coagulant, often rennet, is added and/or the curd is 'cut', and sometimes 'cooked', then drained of whey; some are also pressed. Finally the formed cheese is variously ripened: some from the outside, either by the growth of a white mould or surface bacteria; others internally by their original starter bacteria.
The amount of moisture left in the curds, and the related fineness of the particles, determines the type of cheese; moist cheeses generally being more susceptible to bacteria, ripen faster. Hard cheeses, which have much of their moisture removed, take longer to mature.
The type of milk used also influences the character of the cheese. The differing compositions of milk from different species and breeds, whether it is skimmed, whole or enriched, and whether it is raw or pasteurized, all contribute to flavour, colour and texture in cheese.
The place where the cheese is made also makes a difference. The animal's diet, often geographically specific, plus indigenous air-borne moulds, impart unique qualities to cheese. Many cheeses are named for their place of making.
Their diversity of styles and tastes makes classifying cheeses difficult. As well as milk type and origin, they are frequently grouped by the nature of their rind and their overall texture.
An egg is a spheroidal reproductive body, laid by a female animal. Containing the potential embryo and, importantly, its food reserves, enclosed in a shell or membrane, eggs are extremely nutritious. All eggs consist of a thick, viscous, transparent liquid "white" surrounding a round sac of opaque yellowish "yolk". The white is composed of mostly water and some protein; the yolk of protein, water and fat.
Being porous, egg shells are pervious to odours, water and air. At the large end of an egg is an air pocket, which enlarges as the egg ages. The freshness, or otherwise of an egg can thus be tested by whether it contains suficient air to float.
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