Potassium nitrate (Saltpetre)
A naturally occurring mineral generally caused by the oxidation of nitrogenous matter in the presence of alkalis and alkaline earths. It occurs as crusts on walls, rocks, and in caves from where it derives its name, from the Latin sal petrae - salt of rock. It also forms in certain soils in, Egypt, India, Iran, Italy and Spain, with deposits in the great limestone caves of Indiana, Kentucky and Virginia.
It can also be artificially manufactured by the reaction of potassium chloride with nitric acid or, importantly for vegetarians or those trying to avoid GM foods, from waste animal and vegetable matter.
It is white in colour, soluble in water, and has a cool and salty taste.
Potassium nitrate is probably better known for its use in blasting powders and fireworks or as a fertiliser for intensive crops such as tomatoes and potatoes but as a food preservative it is one of the most effective (and oldest) ways of preserving meat. In inhibiting the growth of the bacterium responsible for botulism, Clostridium botulinum, it has probably prevented many deaths.
Whilst in general it is rapidly excreted, under some specific conditions it may be converted in the stomach and saliva to potassium nitrite, which can prevent haemoglobin in the red blood corpuscles performing as an oxygen carrier. This can lead to cyanosis, sometimes called 'blue baby syndrome' in infants. Nitrites can also produce potentially carcinogenic nitrosamines.
In addition, prolonged exposure to even small quantities may cause anaemia or kidney inflammation, with ingestion of large amounts possibly causing severe abdominal pain and vomiting, muscular weakness, vertigo and irregular pulse.
Used in Dutch cheese as well as many meats, such as, cured meats, bacon, ham, tongue, sausages, smoked frankfurters, pressed and tinned meats.
Occurring naturally in body fluids and plant juices acetic acid, also called ethanoic acid, is the most important of the carboxylic acids. It is an important metabolic intermediate being involved in fatty acid and carbohydrate metabolism.
In one of its most common forms, vinegar, (from the French vin, wine; aigre, sour - giving away its origins), it has been used as a preservative since ancient times.
Vinegar can be made from any liquid that is capable of being converted into alcohol in a two-step process. During fermentation the sugar in the liquid is converted into alcohol and carbon dioxide gas by the actions of yeast enzymes. Then, in a process first described by the French physicist Louis Pasteur in 1864, the alcohol then combines with atmospheric oxygen by the action of Acetobacter bacteria, forming acetic acid and water. (Although it was early in the 18th century that a Dutch technologist, Hermann Boerhaave, found that the rate of acid production was directly proportional to the amount of surface exposed to air).
It is because of the variety of source materials, and the differing organic acids and esters derived from that source material which are also present, that are responsible for the different flavours and aromas of vinegar, for example, grapes - wine vinegar, apples - cider vinegar, malted barley or oats - malt vinegar.
In addition to the method for producing vinegar, large amounts of acetic acid are prepared synthetically either by acetylene being hydrated to acetaldehyde, which is then oxidized or by a process using methanol, from gas or oil, and carbon monoxide.
Pure (over 99%) acetic acid, is called glacial acetic acid, and is a corrosive, colourless liquid with a boiling point of 117.9 C. which is completely miscible with water. It is so corrosive that it could burn through the oesophagus and it has been used in products to remove warts and corns.
In foods it is used for its antibacterial properties, as an acidity stabiliser, diluting colourings, as a flavouring agent and for inhibiting mould growth in bread. In brewing it is used to reduce excess losses of carbohydrate from the germinated barley and to compensate for production variations, so producing a consistent quality beer.
It can be found in beer, bread, cheese, chutney, horseradish cream, pickles, salad cream, brown sauce, fruit sauce, mint sauce and jelly and tinned baby food, sardines and tomatoes.
Lactic acid, an organic compound belonging to the family of carboxylic acids, occurs naturally in the blood (in the form of its salts, called lactates) when, during exercise, glycogen is broken down in the muscles. It can be converted back to glycogen in the liver. Also occurs naturally in sour milk as the result of bacteria activity, molasses, fruit and some seeds during germination.
First isolated in 1780 by a Swedish chemist, Carl Wilhelm Scheele, it is usually obtained commercially by heating and fermenting carbohydrates such as sucrose, molasses, starch, or whey.
As a food additive it increases the antioxidant properties of other substances and can be used to add a bitter taste. In brewing it is used to reduce losses of carbohydrates from germinated barley and for adding to the malt slurry to assist in making a beer of consistent quality.
It is the commonest acidic constituent of fermented milk products such as sour milk, cheese, and buttermilk.
Used in beer, cheese, carbonated drinks, jams, jellies, soft margarine, marmalade, infant milks and cereals, pickled red cabbage, salad dressings, sweets, tartare sauce and many tinned products, such as babyfoods, mackerel, pears, sardines, strawberries and tomatoes.
Vegetarians should be aware that as it is a naturally occurring animal product it could conceivably be of animal origin.
Ascorbic acid (Vitamin C)
Vitamin C, essential for growth, healthy teeth, gums, bones, skin and blood vessels and aiding the absorption of iron, is found naturally in many fresh fruits and vegetables.
It is commercially manufactured by several different methods, however one in particular should be noted. This involves a fermentation process using the genetic material of two enzymes from different bacteria being transferred to a single bacterium - Genetic Modification.
It is used as an antioxidant in the brewing industry where it improves the shelf life of beers and prevents haze development, a preservative in the meat industry where it helps maintain colour, an improving agent in the baking industry and also for inhibiting discolouration in cut fruits, fruit pulp and juices.
In addition to its use in these areas it can also be found in butter, frozen egg products, powdered and concentrated milk, frozen croquette potatoes, tinned baby foods and wine. It can also be added to products that may lose their vitamin C in processing - such as dried potatoes.