by Tom Stobart
A few modern methods are important industrially but not possible in the home – for example, the removal of micro-organisms from liquids by filtration which, if done effectively, will make them keep. The shelf life of *flour is much increased by the removal of the germ from the grain – nutritionally a harmful practice. In some cases, the enzymes in the germ are inactivated by heating before it is returned ‘dead’ to the flour.
PRESERVATIVES are substances that are added to foods to make them keep; they destroy or at least discourage micro-organisms or slow down natural processes that cause spoilage. Into the last category come anti-sprouting agents, which are sprayed over vegetables, mainly potatoes, to prevent them sprouting in store. For their safeness, we can only trust to the vigilance of the governmental agencies which monitor our food.
Although the term preservatives conjures up thoughts of sinister additives produced by the petrochemical industry, the description covers many things that food manufacturers would consider old fashioned or downright folksy. Herbs and spices contain essential oils which can be antiseptic, often quite strongly so; thymol, which is found in thyme, is used in mouth-washes.
Cloves, cinnamon, white mustard and even pepper have similar properties. The preservative action of spices is important in sausages and pickles, while curries will keep sweet for several days in the hot Indian summer. White mustard seed is particularly effective in chutneys. A clove in stock will help keep it sweet as well as adding background flavour.
The most important traditional preservatives are salt (in *brines and *dry-salting), sugar (in *jams), vinegar (in *pickles) and *lactic acid (which is produced in sauerkraut and fermented pickles). Various nasty substances, including *disinfectants such as formaldehyde, which were used in the past as preservatives, are now generally forbidden. Some preservatives which are purely industrial in application are outside the scope of this book For example, carbon dioxide under great pressure stops yeasts from growing and is used to hold fruit juices, such as crude apple juice, in bulk before filtration, sterilization and bottling.
Most preservatives are acids – in sufficient strength, and given sufficient time to operate, any acid will prevent putrefactive bacteria from growing and will kill disease organisms. The hydrochloric acid in the stomach kills most of the bacteria that we eat. Certain acids, though, have antiseptic properties over and above those that result from their acidity. They thus come into the category of chemical preservatives.
Apart from germ killing, the other important preservative function is preventing oxidation. The effect that oxygen can have on food is demonstrated by the way that cut surfaces of apples or potatoes turn brown when exposed to the air. Oxygen is a prime destroyer, which attacks many foods, helped by enzymes and the ultra-violet rays in sunlight. Oxidation destroys such vitamins as vitamin E very quickly and turns fats rancid. In the kitchen, discolouration of vegetables and fruit is prevented by using lemon juice. Commercial anti-oxidants include sulphurous acid and its derivatives.
*Acetic acid is the acid of vinegar, for which it is used as a substitute in some cheap pickles.
Benzoic acid and sodium benzoate. Benzoic acid was discovered in gum benzoin in 1608 and prepared from urine by Scheele towards the end of the 18th century. It can be bought from pharmacists in the form of white, shiny needles. More commonly used as a preservative is the sodium salt, a crystalline powder with a sweetish, astringent taste. Sodium benzoate is slightly alkaline (pH 8), but must be used in slightly acid conditions if it is to be effective as a preservative (in an alkaline medium, such as milk, it has almost no preservative effect). In the countries including the UK and US – where sodium benzoate is allowed, 1 part per 1,000 is considered safe. lt is used particularly in fruit juices and tomato sauces (which are acid) to prevent spoilage after opening. Cranberries, which have remarkable keeping qualities, contain natural benzoic acid.
Boric acid is a mild antiseptic, which used to be a standard item in medicine cupboards. It was once a common preservative for margarine, butter, cream, caviar, ham, etc. Most foods are preserved by 0.5% of boric acid, but it is now banned for commercial products in the UK and US, though many other countries allow it. There is probably no harm in its occasional home use, provided the dosage is properly measured, but few recipes specify it.
*Citric acid is an anti-oxidant and a weak preservative. However, bottled lemon juice has to be treated with sulphur dioxide, which has the same properties much more strongly.
*Lactic acid is unusual in being a preservative that is normally formed in foods by fermentation rather than added to them.
Salicylic acid and its sodium salt sodium salicylate have been used as commercial food preservatives in some countries but are forbidden in others. Salicylic acid is chemically related to aspirin – acetylsalicylic acid – and is medically used in rheumatic liniments and for treating corns (it loosens, swells and softens the surface cells of the skin). It is poisonous if used too freely over a long period, and some people are allergic to it, as others are to aspirin. However, recipes from Italy use salicylic acid as a preservative in home-made tomato concentrates at the rate of 1 gram per kg (2¼ lb) and no more. At this rate, and for home use, when you know how much you are using the preserved food, it must be relatively harmless, but like any chemical it is not something to throw in by the handful. The advantage of such chemical preservatives over complete sterilization by heat, is that they do not alter the flavour.
Sorbic acid is used to stop the growth of moulds on cheese and bread.
Sulphur dioxide (SO2), sulphurous acid (H2SO3), and sulphites. Sulphurous acid is not known in a pure state, but, at least in theory, is formed when sulphur dioxide (for instance, from burning sulphur) is dissolved in water. Sulphurous acid and sulphites are toxic to all micro-organisms, but especially so to wild yeasts. Metabisulphites, particularly in the form of *Campden tablets, are the most convenient source of sulphur dioxide on a domestic scale. In this form, they are invaluable to home makers of wine, beer and cider. Sulphur dioxide is also used in fruit juices and in the drying of fruit. There are limits in most countries on the concentration of sulphur dioxide and its derivatives permitted in foods. Sulphurous acid is also an anti-oxident and a bleach.
[Preservative – French: préservatif German: Schutzmittel Italian: preservativo Spanish: preservativo]
PRESERVED FRUIT. See candied fruit
PRESSURE sometimes has to be applied with a weight – for example, to cheese, gravlax, tongue and terrine – or even with a special press, as used with duck to squeeze out the juices. Most serious cooks have their own favourite weights – old kitchen weights, stones, bricks wrapped in polythene bags and so on. The use of weights bears thinking about since the right pressure for any job has some importance. Pressure of this type is used to squeeze out juices, to firm, to remove air pockets, to shape, or to make food stay in contact with the heat, as in frying a spatchcocked chicken for recipes such as polio alla diavola.
The main significance of pressure to the cook, though, is its effect on the boiling point of water, both with variations of *altitude and in *pressure cooking.
[Pressure – French: pression German: Druck Italian: pressione Spanish: presión]
PRESSURE COOKING. The higher the pressure, the higher is the temperature at which water boils. Thus, increasing the pressure allows a vessel containing water to reach a higher temperature than the 100°C (212°F) at which it would otherwise stay until all the water had boiled away.
The principle is used in the pressure cooker and autoclave (the large scale equivalent of the pressure cooker used in commercial canning and for sterilizing in the operating theatre).
The first pressure cooker, known as the digesteur d’aliments, was invented in 1675 by a Frenchman, Denis Papin. In this, the top of the vessel was held down by a huge clamp, and the valve – where the steam escaped when the set pressure was reached – was held down and adjusted by a long arm with a weight sliding on it (Papin subsequently settled in England a
nd worked with Robert Boyle on the steam engine.)
The modern pressure cooker is much simpler but the principle is the same: sealing in the steam to cause an increase in the pressure and therefore in the temperature. The higher temperature results in more rapid cooking; it can cut times by at least two thirds.
Household pressure cookers are made of aluminium or stainless steel; they should last for many years if looked after carefully. The basic components of a pressure cooker are: a body and cover made of a gauge of metal that will withstand at least six times the maximum cooking pressure, a pressure control, a safety plug, a gasket or sealing ring, and a locking device to keep the cover firmly pressed down.
Separators allow more than one food to be cooked at a time – perforated separators are for small or cut fruit and vegetables; solid ones are for rice and for tinned and frozen foods. A trivet may be used to keep the contents away from the bottom of the pan. Many versions have more than one level of pressure.
High pressure (15 lblsq. in. or 1.05 kglsq. cm.) is for everyday boiling, stewing, braising and pot-roasting meat, poultry, fish, vegetables and milk puddings.
Medium pressure (10 lblsq. in. or 0.7 kglsq. cm.) is for softening fruit for jams, jellies and marmalade, cooking vegetables for chutneys and sauces and for blanching vegetables for freezing.
Low pressure (5 lblsq. in. or 0.35 kglsq. cm.) is for steaming puddings and preparing fruit for *bottling. The liquid used for pressure cooking should never be less than 250 ml (½ pt) -don’t forget it. A pressure cooker can work only if it has liquid inside to produce steam. The amount of liquid used depends on the type of dish and the length of cooking time, but not on the quantity of food being cooked. The liquid itself must be one that produces steam when it boils – such as water, stock, soup, gravy, wine, beer, milk- and not fat or oil alone. However, watery foods like meat can produce a lot of their own liquid. Don’t fill a pressure cooker more than two-thirds full with solid foods, as the steam must circulate freely. With liquids such as soup, milk puddings or fruit, do not fill the cooker more than half full, to allow room for them to rise when they come to the boil. The manufacturer will supply a book of instructions with the pressure cooker, to start with, you should accurately follow the timings quoted for cooking.
Pressure cookers are excellent for many foods. They enable vegetables such as beetroot and potatoes to be quickly steamed with little loss of nutrients, and they save time and fuel. They are not ideal for dishes in which flavours must amalgamate and temper over a period of time. Their drawback is also that as the container is sealed one cannot test, taste or stir without removing the lid; to do that, pressure must first be reduced by cooling in a basin of cold water under a running tap. The sudden reduction of pressure can sometimes destroy the texture of what is being cooked.
PRICKLY PEAR, Cactus pear, Indian fig, Indian pear, Barbary pear or tuna fig is not related to the pear or the fig but is the fruit of Opuntia, the familiar cactus which has large plate-like pads. The best fruit are said to come from O. magacantha, a native of Mexico, but the prickly pear that grows in Europe is O. fiscus-lndica, which is well established in the Mediterranean and North African areas, but also came from Mexico.
The fruits, which have very nasty spines, are borne along the edges of the green pads and, when ripe, are yellow-green, rosy-red, purple or almost black. Although some sorts are small, the largest reach 12 cm (5 in) long. Some plants produce two sets of fruit; the second crop- ripe in October and going on to December- are larger and better to eat. Prickly pears can be fairly tasteless, like slightly sweet, over ripe cucumbers, with lots of small seeds embedded in the flesh, but some varieties can be good. In the US, the best are large and rose coloured, but in Europe – especially in Sicily- the nicest ones have whitish or yellowish fruits. In Sicily, these are called bastardi or bastardom: They keep through to January and are often cut with a small piece of the pad attached to keep them fresh.
To gather the fruits, you need to have your hands well protected, as the spines are tiny, irritating and difficult to get out of your skin. When the fruits have been cut off, the spines must be rubbed off them and rinsed away. Even so, it is safest to extract the pulp while holding the fruit with a thick cloth, tongs or leather gloves. Cut off both ends of the fruit, and slit the skin from end to end, so that the pulp can be loosened and removed. This can be chilled and eaten raw, but may need a squeeze of lime or lemon, as it tends to lack acidity.
The pads of the prickly pear are eaten in Mexico, where they are called nopales (the fruits are called nopalilas or tunas). Very young pads are best and should have the spines but not the skin removed before cooking. They are then cut into small pieces (about 1 cm or ½ in thick) and cooked in well salted water until they are tender. They are then drained and washed under the cold water tap until they are no longer slimy. They are used in soups, cooked as a vegetable, or added to the vegetables for a Spanish type omelette. They may also be slivered and eaten raw with scrambled eggs.
Nopales are available canned en *escabeche, in vinegar, in brine, and in water (nopalitos tiernos al natural, the best to use). Fresh ones appear in US markets that sell Mexican ingredients, but they are not used in Europe, although they could well be in the Mediterranean countries.
[Prickly pear – French: figue de Barbarie Italian: fico d’lndia Spanish: higo chumbo]
PRIMOST. See whey.
PROOF SPIRIT. This is not pure *alcohol but an antiquated concept fortunately becoming obsolete as it caused confusion. An old description is as follows: ‘Formerly a very rude mode of ascertaining the strength of spirits was practised called “The Proof”. The spirit was poured upon gun-powder and inflamed. If at the end of the combustion the powder took fire the spirit was said to be “over proof”. If the spirit contained much water the powder was rendered so moist that it did not take fire, in which case the spirit was said to be “under proof”.’
Proof spirit became defined by act of Parliament in the reign of George Ill as ‘such as shall, at the temperature of 51 degrees of Fahrenheit’s thermometer weigh exactly twelve thirteenth parts of an equal measure of distilled water.’ In more modern terms, British Proof is roughly 57% per cent alcohol by volume at 15°C (60°F), or virtually 50% by weight (a measure which is of course independent of temperature). Its specific gravity is close to 0.8 at 60 °F. The US, in an attempt to rationalize the system, redefined proof spirit as to 50% alcohol by volume.
Many labels still express alcohol content as a percentage of proof strength. To convert British proof to degrees Gay Lussac (effectively the percentage of pure alcohol) multiply by 4 and divide by 7. Gay Lussac to proof, multiply by 7 and divide by 4. US proof to Gay Lussac, divide by 2. Gay Lussac to US, multiply by 2. US proof to UK proof, multiply by 7 and divide by 8. UK proof to US proof multiply by 8 and divide by 7.
PROSCIUTTO. See ham (Italian).
PROSO. See millet.
PROTEINS are exceedingly complex, organic nitrogen compounds which form part of all living cells and are in a sense the basic stuff of life itself Enzymes, for instance, are proteins. They are particularly concentrated in meat and fish, in cheese and eggs, in nuts and in legumes – especially soya beans. Proteins differ widely in their characteristics. Some are soluble or easily mixed with water (such as egg white) while others (such as the casein from milk) are insoluble. Proteins start to coagulate at 50-60°C (122-140°F) and are completely coagulated at around 65-70°C (149-158°F) but some need higher temperatures (e.g., milk protein 100°C or 212°F). Proteins may harden to horny substances when strongly heated. Thus, egg white, when heated, at first becomes solid and insoluble, but, when fried in very hot fat, it becomes downright hard and brittle. However, coagulated proteins can be hydrolysed by acids and enzymes into their constituent building bricks, the *amino acids, and most are broken down by the digestive enzymes in our bodies. The breaking down can also be achieved by long, slow cooking, but dry heat can destroy amino acids, particularly lysine.
The daily req
uirement of protein for an adult would be satisfied by about 225 g (½ lb) of meat or chicken per day with no protein coming from any other source, but most people in Europe and America get their requirements from a mixed diet, and 100-150 g (4-5 oz) of meat a day is enough.
[Protein – French: protéine German: Protein Italian: proteina Spanish: proteina]
PROTOZOA are microscopic, single-celled (or non-cellular) animals. The parasitic forms have complicated life cycles and cause many nasty tropical diseases, such as malaria, sleeping sickness, amoebic dysentery and bilharzia. The most effective precaution against waterborne protozoans in the tropics is boiling; covering food and water helps protect against protozoans carried on flies. Marine protozoans are an important element in plankton and form part of the food of many shell fish. Some are poisonous, and may be dangerous when they are present in exceptionally large numbers, as in the notorious ‘red tides’ (see poisoning).
PRUNE. See plum
P’SST. See monosodium glutamate.
PTARMIGAN. See grouse.
PTOMAINE. See poisoning.
PULASAN. See lychee.
PULSES. The general term for all ripe, dried, edible seeds of *legumes: peas, beans, grams and lentils. They are the main source of protein for poor people, but their use is particularly developed in vegetarian India.
Pulses are generally soaked before cooking; the drier they are, the longer the soaking needed. However, in warm weather, an unpleasant fermented taste may result from the activity of micro-organisms or from the onset of changes leading up to germination. It is probably better to cook pulses without soaking whenever possible. Exceptions are very old, dry beans or very large beans which have to be kept looking nice, with their skins on, to be used, for example, in an hors d’oeuvre. For such purposes, large beans are best given a very full soaking in the refrigerator, so they look thoroughly plump, not wrinkled, before they are cooked. Bicarbonate of soda in the water helps to soften the skins.