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The acidity is the number of free hydrogen ions available. In food acids cause a sour taste. Basically the more sour the food the greater the acidity. Acidity is measured by pH. The lower the pH the higher the acidity.

See pH.


Additives are chemicals which are added to food to perform many functions, including: extension of shelf life (preservatives); improving taste (flavourings), or appearance (colourings), or texture, or even improve the nutritional value of the food (adding vitamins or minerals). Additives are often only safe at low concentrations so the amount of additive added should be carefully controlled.

See preservatives.


Aerobes are life forms which need to use the oxygen in air in order to live. All animals, including us, are aerobes. Most yeasts and moulds are aerobes. Bacteria are basically divided between those which need oxygen (aerobes) and those which can survive without oxygen (anaerobes).

See air, anaerobes and oxygen.


Above the land and sea, our planet is surrounded by a gaseous layer (known as the atmosphere) made up of air. Air consists of a mixture of gases, the most important ones being oxygen, nitrogen and carbon dioxide.

See aerobes, anaerobes and oxygen.


Aluminium is a metal used in the manufacture of some types of pots and pans. However aluminium is attacked by acids and aluminium can migrate into the food if the pans are uncoated. Aluminium can act as an accumulative poison and has been linked with types of dementia.


Anaerobes are life forms which which can survive without the oxygen in air Some anaerobes are actually killed by oxygen. Green plants can live anaerobically. As far as food hygiene is concerned the most important anaerobes are the Clostridium group of bacteria, including Clos. perfringens and Clos. botulinum. Clostridium bacteria can only grow in the absence of oxygen.

See Aerobes, air, oxygen and Clostridium.


Antibiotics are chemicals produced by microbes (normally moulds but sometimes bacteria) which kill or prevent the growth of other microbes (normally bacteria). The most frequently used antibiotic used to treat disease in man is penicillin. Antibiotics are also used to prevent and cure disease in farm animals and if care is not taken these antibiotics can be present in our food.


Antimony is a metal which is found in enamel and can migrate into food from chipped enamel, especially when used to store acidic food. Antimony can accumulate in the body and cause damage to the nervous system.

Aseptic conditions:

Aseptic conditions means an environment free of microbes. Aseptic conditions are needed when packing sterilised food into sterilised containers. Aseptic conditions are usually created in a small localised area by sterilising the air and enclosing surfaces either with steam or chemicals.


Bacillus cereus:

Bacillus cereus (from Latin, meaning waxy rod) is a spore forming bacteria which produces a toxin when growing in food. This toxin, when eaten with the food, causes inflammation of the stomach, hence stomach pains and vomiting. Cooked rice is the food most commonly associated with this type of food poisoning.


Bacteria are a large group of single celled microscopic life forms whose genetic material (D.N.A.) is not bound within a membrane or stabilised by special proteins (known as histones).

See microbes.


A bactericide is any chemical which kills bacteria. The bactericidal power of a disinfectant means its effectiveness at killing bacteria. The suffix cide is derived from the Greek meaning killer.

See bacteria and disinfectant.

Barrier creams:

Barrier creams are hand creams used to protect hands from drying or cracking. Rough cracked skin harbour more bacteria than smooth skin, so food grade barrier creams should be used by food handlers.

Best Before:

A 'Best Before' date is applied to food in which the microbes are either dormant or dead, hence spoilage is normally due to slow chemical changes occurring within the food. Only low risk food, as far as food poisoning is concerned, should have a 'Best Before' date and all other food should have a 'Use By' date. Often 'Best Before' dated food has to be stored under appropriate conditions to last until its 'Best Before' date. e.g. most frozen food needs to be stored at -18ºC and dried food should be stored in a cool dry place.

See high risk food, low risk food and 'Use By'.

Biological contamination:

Biological contamination is any matter of plant or animal nature, which when added to food matter makes it unfit to eat. The most common type of biological contamination is human hair but other types include animal hair, bits of insects, rodent or fly droppings and toadstools.

See contamination and unfit food.


Blanching is the immersion of fruit and vegetables in boiling water or steam in order to destroy enzymes which will otherwise cause undesirable chemical changes in the product. Blanching is derived from the French for white, as fruit and vegetables lose colour during the blanching process.


A boil is an infection in the base of a hair which causes the surrounding skin to swell. The swelling contains pus. Boils are caused by and contain Staphylococcal bacteria, some of which can cause food poisoning. Hence food handlers should keep all boils covered.

See pus and Staph. aureus.

Botulinum cook:

The botulinum cook is the amount of heat processing required to reduce the chance of survival of a botulinum spore to 1 in 1,000,000,000,000. Low acid food (above pH 4.5) sealed in an air tight container, such as a can, stored above 3ºC, requires a botulinum cook. Normally this consists of heating the food to a core temperature of at least 121ºC for 3 minutes.

See botulism, Canning, Clostridium botulinum and heat processing


Botulism is a severe type of food poisoning caused by eating food contaminated by the toxin produced by Clos. botulinum. The toxin attacks the nervous system and usually results in death within 2 to 8 days if the patient is untreated. The foods at greatest risk are canned, bottled or vacuum packed food where the pH is above 4.5.

See Clostridium botulinum and pH.

Bound water:

Bound water is water which is unavailable for microbial growth. e.g. sugar binds water to it, so microbes cannot grow on properly manufactured golden syrup as all the water is bound.

See free water and water.



C.I.P. is short for Cleaning In Place and is an automatic cleaning system used for cleaning industrial equipment and machines without having to dismantle the equipment. The C.I.P. is normally controlled by a computer or microprocessor and the program should not be short cutted or altered without expert advice.


Canning is the process of storing food in tin plated, lacquered steel containers which have been sterilised by heat treatment. The amount of heat needed for sterilisation depends on the pH of the food and the size of the can.

See lacquering, pH and sterilisation.

Carbonised food:

Carbonised food is food which is burnt in frying, roasting or baking. In industry carbonised food can accumulate on heat exchangers. These burnt food stains cling to surfaces and are difficult to clean.

Central kitchen:

A central kitchen is where the food is prepared, cooked, portioned then either chilled or frozen in a Cook-chill or Cook-freeze operation. A central kitchen normally also has a chilled storage area for Cook-chill or Cook-freeze food.

See Cook-chill, Cook-freeze and feeder kitchen.

Chemical contamination:

Chemical contamination is when food fit for human consumption is made unfit for human consumption by the addition or migration of harmful chemicals into the food.

See contamination and unfit food.

Chemical migration:

Chemical migration is when chemicals move from the food container into the food causing chemical contamination. Examples are antimony from cheap enamel saucepans and poisonous chemicals from non-food safe plastics.

See antimony and contamination.


Chilling is the process whereby food is cooled to a temperature between 0 and 5ºC, then stored at this temperature. Chilling takes high risk food out of the danger zone and protects food from food poisoning and microbial spoilage by slowing microbial growth.

See danger zone, food poisoning, high risk food and temperature.


Chlorination is the addition of chlorine gas to water to prevent the growth of microbes in the water. In canning the amount of chlorine in the cooling water needs to be checked to ensure that the concentration of chlorine is high enough to disinfect the water, but not too high, otherwise the chlorine might cause chemical contamination of the food or corrode the can.

See chemical contamination, disinfection and leaker spoilage.

Clarification (milk):

Clarification is the removal of sediment and bacteria from raw milk by centrifuging it. The milk is span at a fast speed, causing the sediment and bacteria, which is heavier than the milk to move furthest away from the centre of the centrifuge, where it can be collected in collecting bowls.

Clean As You Go:

Clean As You Go makes it the responsibility of all food handlers to keep their work area clean and wipe up spillages as soon as they occur, before they become engrained.

See food handler and spillages.


Cleaning is the removal of dirt, dust and food debris from an area or piece of equipment. Cleaning might remove microbes but does not kill them. Normally a cleaning sequence is as follows: Pre rinse (or pre clean); Main clean (with detergent); Rinse; Disinfection (or sterilisation); Final rinse (if a chemical disinfectant was used); drying.

See detergent, disinfection and sterilisation.

Cleaning schedule:

A cleaning schedule as a plan to ensure that all surfaces and all equipment in food areas are cleaned in a systematic way. The frequency of cleaning and the cleaning procedure depend upon the type of dirt and the speed of accumulation of the dirt.

See cleaning.


Clostridium is derived from the Greek for spindle, as this group of bacteria look like spindles when forming spores. Clostridium bacteria can only grow in the absence of air. Two species of Clostridium can cause food poisoning; Clos. perfringens and Clos. botulinum.

See air, Clostridium botulinum, Clostridium perfringens, food poisoning and spores.

Clostridium botulinum:

Clostridium botulinum can grow in food where oxygen is absent, the pH is above 4.5, and the temperature is above 3ºC. When Clos. botulinum grows in food it releases a toxin. If eaten this toxin causes the disease botulism.

See botulism, Clostridium and toxin

Clostridium perfringens:

Clostridium perfringens is an anaerobic, spore forming rod which produces a toxin during spore formation. This toxin causes a form of food poisoning, which is normally mild but it may be more severe in the very young, elderly or infirmed. The foods most commonly associated with this type of food poisoning are large pots of stews and curries or large joints of meat where the heat penetration is poor or where the cooling time is too long.

See anaerobes, Clostridium, food poisoning and toxin.


Cockroaches are beetle like insects, which are usually found in warm areas where food is stored, although one type of cockroach prefers cooler, drier places such as storerooms or basements. All cockroaches can contaminate food and spread food poisoning microbes including Salmonella.

See food poisoning, insects and Salmonella.

Cold spots:

Cold spots are localised areas which receive insufficient microwave energy during microwave cooking. Thus the temperature in cold spots is often too low to kill microbes. Cold spots can be reduced by; turning the food; stirring the food; allowing standing time during and after cooking and not overloading the microwave oven.

See microbes, microwave ovens and microwaves.

Coliform test:

Coliforms are a group of bacteria which are present in water and the guts of people and animals. Some coliforms can cause disease. In the coliform test, liquid (e.g. water or milk) is added to a purple broth in a test tube, with a small inverted tube at the bottom of the test tube. Coliforms produce acid and gas. The acid causes the broth to change colour from purple to yellow and the gas causes the small inverted tube to rise up the test tube.

See bacteria.


Contamination is the addition of a substance (be it microbial, chemical, physical or biological in nature) to a food fit for human consumption which then makes that food unfit for human consumption. Eating contaminated food may cause food poisoning in the case of microbial, chemical or biological contamination or internal injury in the case of physical contamination.

See chemical contamination, food poisoning, microbial contamination and physical contamination.


In Cook-chill, food is prepared, cooked, portioned then chilled to 3ºC in a central kitchen. A safer version is to portion the food before cooking. The food can be stored chilled for up to 4 days. The food is taken to a feeder kitchen where it is reheated prior to being eaten. Cook-chill is used in large scale catering operations such as hospital food or school dinners.

See central kitchen, Cook-freeze and feeder kitchen.


In Cook-freeze the food is prepared then cooked in a central kitchen, portioned then frozen to -20ºC. The food can be stored for up to eight weeks, before it is reheated in a feeder kitchen before being eaten. Cook-freeze produces a higher quality product than Cook-chill and is used by many airlines.

See Cook-chill, central kitchen and feeder kitchen.


Cooking is the application of heat to food in order to kill all active microbes. Cooking does not always kill spores or break down toxins. Hence the safest option is to cook fresh food and eat the food hot, immediately after it has been cooked. The safest cooking method is a short time, high temperature one, which quickly takes the food through the danger zone.

See danger zone, microbes, spores and toxin.

Cross contamination:

Cross contamination is when microbes are moved from a source rich in microbes to a food (normally a high risk food) which initially was virtually free of microbes. The source rich in microbes can be raw food, refuse or soil from vegetables and the vehicle for moving the microbes can be handler's hands, pests, equipment (knives, tongs etc.) or surfaces.

See contamination, food handler, high risk food, microbes and pests


Curd is basically a mixture of milk proteins which go from the liquid state to the solid state as the pH falls, when making cheese.

See pH and whey


Danger zone:

The danger zone is the temperature range in which food (especially high risk food) is at the greatest risk from microbial attack. Food containing active (or potentially active) microbes should be stored or held within the danger zone for the shortest possible time. The danger zone is between 5ºC and 65ºC.

See high risk food, temperature and microbes.


A design is a construction plan. Food areas should be designed to reduce the risk of contamination by keeping cooked and raw food separate. Also all food areas and equipment should be designed so that they are easy to clean.

See contamination.


A detergent is a chemical (or a mixture of chemicals) which can spread over a surface (good at wetting), causing the dirt to go into suspension. Detergents do not kill microbes but can wash away many microbes with the food debris.

See food debris and microbes.


Diarrhoea (which is derived from the Greek meaning flow through) is loosely known as a runny tummy or the runs, is a condition in which there is abdominal pain and very loose bowel movement accompanied by watery stools. Many types of food poisoning can cause this condition.

See food poisoning.


Disinfection is the process whereby microbes are killed until their number is reduced to a safe level. Disinfection can approximately mean killing all active (vegetative) microbes but not the spores. Using hot water above 82ºC for one minute is the most common disinfectant but a range of chemicals can be used. Equipment and surfaces need to be cleaned before they can be disinfected.

See Cleaning,microbes and spores.

Disinfection (milk):

When milk is disinfected it is heated to 100ºC for about 10 seconds. Disinfected milk is not sterile as spores can survive the disinfection process but disinfected milk is more stable than pasteurised milk. Disinfected milk is mainly used for milk products such as dried milk or yoghurt.

See pasteurisation, spores and sterilisation.

Dried food:

Dried food is food in which part of the free water has been removed to protect that food from microbial attack. Dried food should be stored in a dry environment as many dried foods can take in moisture from their environment, thus increasing their water content, so making them vulnerable to microbial attack. Once water has been added to many dried foods they once again become high risk foods.

See high risk food, humidity, microbes and water.


Drip is liquid released during the thawing of meat (including poultry) and fish. Drip might be contaminated with microbes so cooked or ready to eat food stored in the fridge should be protected against drip.

See contamination, microbes and thawing


Environmental Health Officer (E.H.O.):

E.H.O.s are appointed by local authorities to enforce the food laws (Warning UK only). They can also be consulted on any matter concerning food hygiene. E.H.O.s also have other responsibilities including pollution control.


Exhaustion is the process whereby air is removed from cans before they are sealed. Removing the air reduces the stress on the metal during heat processing and cooling as well as reducing the risk from undesirable chemical changes inside the can such as the vitamin loss.

See canning and heat processing.

Exposed food:

Exposed (or open) food is food in which the retailer has to do some work on, besides storing and selling it. Exposed food is more likely to become contaminated, whilst in the retailer's charge, than sealed food, so retailers who deal with exposed food need to have a greater knowledge of food hygiene.

See hygiene and sealed food.


Feeder kitchen:

A feeder kitchen is a place where Cook-chill or Cook-freeze food is reheated before it is eaten. The feeder kitchen should be next to the dining area, or in a hospital on the ward, as the food should be eaten within 15 minutes, after being reheated.

See central kitchen, Cook-chill and Cook-freeze.


Flies are a large group of two winged insects, which include common disease spreading pests such as houseflies and blowflies. These flies can cause food poisoning by contaminating uncovered food.

See food poisoning and insects.


Food consists of a group of chemicals which are essential for life. These chemicals include proteins, fats, carbohydrates, vitamins and minerals. Most food is from plant or animal origin. Food should be appetising, which means pleasing in appearance, taste, smell and texture (or mouth feel). However other life forms are also interested in our food. These life forms include microbes (bacteria and fungi), pests (insects, rodents and pigeons) and even pets (cats and dogs). Hence food needs to be protected from microbes and pests.

See microbes and pests.

Food borne disease:

A food borne disease is a disease in which the food acts as a carrier for a microbe, which can only grow and produce toxins, hence disease, after the food has been eaten. Food poisoning microbes grow in the food whilst food borne microbes do not grow in the food.

See food poisoning and microbes.

Food debris:

Food debris are bits of food which are formed by flaking or falling off the main body of food. e.g. Bread crumbs from a loaf of bread.

Food handler:

Food handlers are people involved in the manufacturing, processing, distribution and retailing of food as well as catering. Food handlers may be in direct contact with food such as food production and catering staff or indirectly such as designers of food equipment or food production areas.

Food poisoning:

Food poisoning is any illness produced by eating food which is contaminated by toxins (or poisons) from microbial, chemical or biological origin. The vast majority of cases of food poisoning in this country are caused by microbes (especially bacteria).

See bacteria, contamination, microbes and toxin.

Foreign bodies:

Foreign bodies is a technical term referring to any extraneous matter, whether of a physical, chemical or biological nature found in food. Examples of foreign bodies are particles of paint, cleaning fluid and human hair. Usually foreign bodies render the food unfit for human consumption. However foreign bodies also include particles of the wrong food such as a butter bean found in a tin of peas. Legally foreign bodies break the Food Safety Act (1990) (Warning UK only) as foreign bodies are not of the substance expected.

See physical contamination.

Free water:

The free water is the part of the water content of food which is available to microbes.

See bound water, microbes and water.


Freezing is the process where by the water component of the food is changed from the liquid phase to the solid phase (ice) in order to protect the food from microbes. To obtain high quality, the freezing should take place as quickly as possible. In frozen food the microbes are dormant rather than dead.


Fungi are life forms in which the genetic material is bound by a membrane (unlike bacteria), but do not produce their own food (unlike plants) and are unable to move on their own (unlike animals). Fungi vary in size from microscopic yeast and some moulds, to visible moulds, to large mushrooms and toadstools.

See moulds, toadstools and yeasts.



H.A.C.C.P. is an abbreviation for Hazard Analysis Critical Control Points. In this system the places where the product is at greatest risk are known as Critical Control Points. These points need to be identified, monitored and controlled.

See hazard analysis.

Hazard analysis:

Hazard analysis means assessing the risks in a catering or manufacturing process and predicting where in the process the risks from microbial, physical and chemical contamination are greatest.

See chemical contamination, H.A.C.C.P., microbial contamination and physical contamination.

Heat exchanger:

A heat exchanger is a piece of equipment in which liquids of different temperature are pumped across either side of a metal plate (or sometimes metal tubes are used with one liquid in the inside and another on the outside of the tube). Heat then flows across the plate (or tube) from the liquid of higher temperature to the liquid of lower temperature.

See temperature.

Heat processing:

Heat processing is the application of heat to food in order to kill all or most of the microbes thus making the food safe to heat. Heat processing might also improve the flavour and texture of food. Cooking is a form of heat processing.

See cooking and processing.

High acid food:

High acid food is food with a pH below 4.5 and does not pose a threat as far as bacterial food poisoning is concerned. However there have been cases of food poisoning caused by pathogenic moulds growing in high acid food. Microbial spoilage of high acid food is usually by moulds and yeasts. Examples of high acid foods are rhubarb and citrus fruits (oranges and lemons).

See acidity, food poisoning, moulds, pathogens and pH.

High risk food:

High risk foods are foods at the greatest risk from microbial contamination, as they readily support microbial growth when kept within the danger zone. Hence high risk food should be stored either below 5ºC or above 65ºC. Unless sterilised then aseptically packed high risk food should have a 'Use By' date.

See aseptic conditions, danger zone, microbes, sterilisation and 'Use By'.


Humidity is the amount of moisture or water vapour in the air. Dried food can take moisture from the air so should be stored under low humidity. However raw meat, fruit and vegetables should be stored under high humidity to prevent them drying out.

See dried food and water.


Hygiene is derived from the Greek goddess for health (Hygeia). The purpose of food hygiene is to ensure that the food we eat is healthy and free from contamination. Food hygiene is about protecting food from microbes, pests, physical and chemical contamination. The most important factors are temperature, time, cleanliness and keeping the food covered.

See contamination, microbes, pests and temperature.


Improvement notice:

An improvement notice (Warning UK only) is a notice issued by a local authority (via an E.H.O.) to a person in charge of a food business stating how the business is breaking the food laws and what actions must be taken in order to comply with the law. An improvement notice is legally binding.

See Environmental Health Officer (E.H.O.).

Ingrained dirt:

Ingrained dirt refers to liquid which has dried onto a surface making it difficult to clean. Often ingrained dirt attracts other dirt and debris by sticking to it, thus causing an accumulation of dirt which attracts microbes and pests.


Insects are a large group of animals whose bodies are divided into three sections (head, chest and abdomen) and have three pairs of legs and two pairs of wings. As far as food hygiene is concerned the most important and dangerous insects are flies and cockroaches, although other beetles play a part in spoilage of food.

See cockroaches and flies.

Integrated cleaning:

Integrated cleaning is incorporating cleaning into the job of all food handlers whose work involves direct contact with food. Integrated cleaning includes Clean As You Go and cleaning schedules.

See Clean As You Go, cleaning schedule and food handler.


The intestine is the part of the gut where the breaking down (digestion) of food is completed and water and nutrients are absorbed into the blood stream. The intestine normally contains a large number of useful and harmless bacteria. However pathogens and poisons from food can attack the intestine causing abdominal pain and diarrhoea.

See bacteria, diarrhoea, food, nutrient, pathogens and stomach.



Lacquer is a resin coating of cans which protect the inside of the can from acids in food which would otherwise attack the metal causing it to corrode. If the can is going to be stored in poor conditions the outside of the can, can be lacquered as well, to protect the metal from corrosion.

See canning.

Lactic acid bacteria:

Lactic acid bacteria are bacteria which convert milk sugar (lactose) into lactic acid and are used in the manufacture of cheese and yoghurt.

See starter culture.

Leaker spoilage:

Leaker spoilage is where a can is spoilt by the can sucking in a drop of cooling water, containing microbes. Leaker spoilage can be prevented by: chlorinating the cooling water; using a good quality of can; and carefully controlling the temperature and pressure changes during heat processing and cooling.

See canning and chlorination.


Listeria (or more accurately Listeria monocytogenes) can cause a food borne disease known as listeriosis, which has 'flu' like symptoms but can cause miscarriages in pregnant ladies. Listeria can survive and grow in a wide range of temperatures from 2 to 75ºC. The foods at greatest risk are soft cheeses, pates, salads and ready to eat meals such as Cook-chill foods.

See Cook-chill and food borne disease.

Low acid food:

Low acid foods are foods with a pH above 4.5 and are at risk from bacterial food poisoning. If low acid foods are to be preserved in cans, bottles or pouches they need to be heat processed to a core temperature of 121ºC for at least 3 minutes (or equivalent) to ensure that they do not cause an outbreak of botulism.

See Botulinum cook, botulism, food poisoning, heat processing and pH.

Low risk food:

Low risk foods are foods which are unlikely to cause food poisoning due to having either a high acid content (low pH; below 4.5) or a low moisture content (or strictly speaking little free water). Normally temperature control is not essential for low risk foods as they usually spoil due to chemical changes. Hence low risk foods have a 'Best Before' date.

See acidity, Best Before, free water, and pH.



Like rats, mice are rodents but much smaller than rats. There are three common groups of mice; house mouse, field mouse and harvest mouse. However most food contamination is by the house mouse, which can also spread pathogenic bacteria. Mice contaminate food with a trail of droppings, spillages and greasy fur marks.

See contamination, pathogens, rats and rodents.


Microbes are a large group of life forms which can only be seen with the aid of a microscope. Microbes are subdivided into bacteria, fungi (which includes moulds and yeasts) and viruses.

See bacteria, fungi, moulds and yeasts.

Microbial contamination:

Microbial contamination is the addition of harmful microbes, either pathogens or spoilage organisms, to food fit for human consumption, making it unfit for human consumption.

See contamination, pathogens and unfit food.

Microwave ovens:

Microwave ovens are metal boxes in which food is heated or cooked by microwaves. The way food is heated depends on the shape of the food and the water distribution in the food.

See cold spots, microwaves and thermal runaway.


Microwaves are a type of high frequency radiation which are absorbed by water molecules, causing them to vibrate and move faster, hence producing heat. This heat can be used to cook and reheat food in microwave ovens.

See microwave ovens.


Moulds are a type of fungi which have multi- nuclei cells and grow by branching out from an area of high mould density. Moulds are involved in the spoilage of food and some produce poisons known as mycotoxins which cause food poisoning.

See food poisoning, fungi and spoilage.



Nutrients are chemicals which are essential for life, which we obtain from our food. These include proteins, carbohydrates, fats, vitamins and minerals.



Oxygen is a gas found in air, which is essential to sustain all animal life forms and many microbes known as aerobes. However some bacteria are poisoned by oxygen so cannot live in the presence of air. These microbes are called anaerobes. Oxygen makes up about 20% of the air.

See air, aerobes and anaerobes.


Pack integrity:

The pack integrity of the food is normally provided by the primary packaging which prevents liquids from leaking out, as well as protecting the food against microbial, chemical and physical contamination.

See contamination and sealed food.


Pasteurisation is a type of heat processing, normally applied to milk and milk products, in which sufficient heat is applied to kill all the harmful microbes. As not all spoilage microbes are killed pasteurised products have a short shelf life and have to be stored chilled.

See microbes and spoilage.


Pathogens are microbes which cause disease. Most microbial food poisoning are caused by bacterial pathogens but some are caused by moulds.

See bacteria, microbes, moulds and toxins.

Personal hygiene:

Personal hygiene is the behaviour that food handlers need to practise to ensure that they do not contaminate the food or cause an outbreak of food poisoning. Examples of personal hygiene include not smoking, wearing protective clothes and reporting of disease.

See contamination, food handler, food poisoning and protective clothes.


Pests are all animals (including rodents, insects, birds and even pets like cats and dogs), which can spread or carry food poisoning microbes or by their actions spoil food.

See food poisoning, insects, pigeons, rodents and spoilage.

Petri dish:

A petri dish or plate is a small round, flat lidded dish (diameter about 10cm.) used for growing microbes. The microbes are either streaked onto solid agar using a loop or a liquid containing microbes is mixed with liquid agar which is allowed to set.

See microbes.


pH is a scale which measures, acidity / alkalinity and ranges from pH1 for strong acids, such as hydrochloric acid, to pH14 for strong alkalis, such as sodium hydroxide. Water has a pH of 7. Low acid foods have a pH above 4.5 and high acid foods have a pH below 4.5.

See acidity, high acid food and low acid food.

Phosphatase test:

Phosphatase is an enzyme produced by most animals and is always present in raw milk. When heated to a temperature around 71ºC the phosphatase enzyme is rendered non-functional for about 2 to 3 days. Hence a phosphatase test can be done to show that the pasteurisation or disinfection of milk has been successfully carried out.

See disinfection (milk) and pasteurisation.

Physical contamination:

Strictly speaking physical contamination should refer to the addition of extraneous matter to food not directly of biological origin such as paper, paint or glass, but legally the term refers to all contamination of a non-microbial source, including human hair, parts of insects and cleaning fluids.

See biological contamination, chemical contamination, contamination and foreign bodies.


Pigeons are birds which are successful in scavenging in towns and cities. They can carry harmful bacteria and contaminate food, given a chance. Pigeon droppings can also damage the fabric of buildings.

See contamination.

Preserving food:

Preserving food involves indirect methods of protecting food from microbes whilst processing involves direct methods such as heat treatment. Pickling in vinegar, salting and adding sugar are methods used in preserving food.

See processing.


Preservatives are chemicals (known as additives) added to food in order to extend the food's shelf life. Preservatives normally work by either inhibiting (slowing down) the growth of microbes or reducing the rate of undesirable chemical changes (e.g. slowing down rancidity in butter).

See additives.


Processing is the direct treatment of food in order to reduce the number of microbes and enzyme activity in that food, hence increase its shelf life. Processing might also improve the flavour and texture of food. Examples of processing include heat treatment, freezing and drying.

See freezing and heat processing.

Product tampering:

Product tampering is when people (human pests) deliberately and often maliciously add physical or chemical (or even microbial) contaminants to food either, for blackmail, revenge or other nefarious reason. Being more intelligent than other pests, human pests are often the hardest to control and protect food from.

Prohibition order:

A prohibition order (Warning UK only) is an order which prohibits certain premises (in whole or in part) or processes or people being involved in the food business. A prohibition order might be issued by a court after a conviction or in an emergency by an E.H.O. on behalf of a local authority. An emergency prohibition order has to be confirmed by a court within three days of issue.

See Environmental Health Officer (E.H.O.).

Protective clothes:

Protective clothes are clothes worn by food handlers to help to protect the food from contamination. Outside clothes are unsuitable in food areas as outside clothes might contain loose fibres which could cause physical contamination as well as a large number of microbes (as in the case of outside shoes).

See contamination and food handler.


Pus is a mixture of white blood cells and bacteria which forms at the site of an infection, such as a boil. Pus often contains Staph. aureus microbes so food handlers must keep all infected areas covered and prevent pus coming into contact with food.

See boils, food handler and Staph aureus.



Rats are a group of rodents; the most commonly ones found in England being the brown rat. The brown rat is brownish grey in colour and has a tail slightly shorter than its body. Rats carry many pathogens, including Salmonella, and their droppings (and even fur) can contaminate food.

See contamination, pathogens and rodents.


Rennet is an enzyme (biological catalyst), obtained from calf's stomachs, used in the manufacture of cheese. The rennet helps to bring the proteins, which will form the curd, out of solution.

See curd.


A retort is a machine similar to a domestic pressure cooker, where batches of cans are heat processed under pressure. The retort has temperature and pressure gauges and should also have temperature / time recording charts.

See canning and heat processing.


Rodents are a group of animals whose front two teeth (incisors) grow throughout their lives, hence their constant gnawing habit or drive.

See mice and rats.



Salmonella are rod shaped microbes (named after Dr. E. Salmon) which is responsible for a severe and sometimes fatal (especially in the very young, elderly and infirm) form of food poisoning, normally associated with poultry, eggs and fish. The microbe itself acts as a toxin and does not produce a spore. The main causes of Salmonella food poisoning are inadequate heat treatment (cooking) and cross contamination from raw to cooked food.

See cooking, cross contamination, food poisoning and toxin.


A sanitiser is a cleaner which contains both detergents and disinfectants. To sanitise is to reduce the number of microbes to a safe acceptable level. If the surfaces or equipment, to be cleaned, are very dirty or contain a very large number of microbes a separate detergent and disinfectant should be used.

See cleaning, detergent and disinfection.

Sealed food:

Sealed food is food which arrives at the retailer pre-packed and pre-portioned but it is the retailer's responsibility to store the sealed food under the appropriate conditions and handle it properly whilst the food is under his charge.

See exposed food.

Service catering:

Service catering means providing meals and snacks mainly to satisfy a need rather than to make a profit. Examples of service catering are work's canteens, school meals and meals on wheels.

See trade catering.


Sewage is liquid waste which leaves houses and factories by underground pipes called sewers. The sewage is filtered then treated with bacteria before being released into rivers or into the sea. However untreated sewage can contain pathogenic bacteria.

See bacteria and pathogens.


Spillages are powders or liquids which escape from their container, causing a mess on floors, walls or work or equipment surfaces. If not cleaned up immediately food spillages attract microbes and pests and liquid food spillages become engrained onto surfaces making them harder to clean.

See Clean As You Go, microbes and pests.


Food spoilage is the process where by food fit for human consumption becomes unfit due to changes brought about either by microbes, pests or chemicals within the food. Microbes and pests can spoil food rapidly whilst chemical changes within food usually take a lot longer.

See microbes and pests.


A spore is a small protective encasement which allows some bacteria and fungi to survive in harsh conditions. Whilst in the spore form the microbe is dormant and much harder to kill than when the microbe is in the active form. Fungi also use spores as part of their reproductive cycle as well as for surviving in harsh conditions.

See bacteria and fungi.

Staph. aureus:

Staphylococci aureus is derived from the Greek, meaning golden bunches of grapes and berries, as Staph. aureus are small spherical clamps (which look like bunches under the microscope) which are non-spore forming but produce a heat resistant toxin. The toxin is responsible for a type of food poisoning which lasts between 6 and 24 hours. Fatalities from this food poisoning are rare. The main risk of Staph. aureus food poisoning comes from poor personal hygiene, especially the mouth or nose to hand to food route.

See food poisoning, personal hygiene and toxin.

Starter culture:

A starter culture are strains of Lactic acid bacteria which are added to milk, when making yoghurt or cheese, in order to increase the acidity so that some of the milk proteins come out of solution. In making some soft cheeses, strains of mould are also added to the starter culture.

See Lactic acid bacteria.


Sterilisation is the killing of all microbes to a level that the chance of survival of any microbe, both active or spore, is very low. Sterilisation is usually by heat treatment but chemicals or radiation might also be used.

See spore.

Sterilisation (milk):

Sterilisation of milk is the killing of all the microbes in milk either by retorting milk in pressure resistant glass bottles or by heat processing the milk, then filling the milk into cartons or plastic bottles under aseptic conditions. Sterilised milk does not need to be stored chilled before being opened.

See aseptic conditions, heat processing and U.H.T. milk.

Stock rotation:

Stock rotation means using oldest stock first, to ensure that food is used within its 'Use By' or 'Best Before' date. This is to prevent stock losses and reduce the chance of pest attack.

See 'Best Before' and 'Use By'.


The stomach is the part of the gut where food is broken down (digested) by the action of acid plus enzymes. The conditions in the stomach are too acidic for most microbes to grow in. However microbial produced toxins can upset the stomach causing vomiting.



Temperature is a measure of the amount of heat within a substance. The higher the temperature the greater the amount of heat or internal motion in the substance. Microbes need some heat for growth but too much heat is fatal to them.

See danger zone and microbes.


Thawing is the process in which ice is converted back into liquid water. Hence thawing is the reverse process to freezing. Food (except for small pieces) should be thoroughly thawed before cooking to ensure an even distribution of heat. Food should be thawed in a covered container in a cold store or fridge at a temperature less than 5ºC. Food which is thawing should be kept separate from other food to prevent cross contamination by drip.

See cross contamination, drip and freezing.

Thermal runaway:

Thermal runaway is when the microwaves are focused, usually by round objects such as apples, causing localised burning whilst other areas receive insufficient heat. This problem can be reduced by turning the food and allowing standing time during and after cooking.

See microwave ovens and microwaves.


A thermometer is an instrument used for measuring temperature. The popular mercury in glass thermometer should not be used in food areas. These days probe thermometers relying on bimetalic strips are popular in the food industry. They should be calibrated against a standard thermometer in ice at 0ºC and in boiling water at 100ºC before use and at frequent intervals depending on the supplier's advice.

See temperature.


Toadstools are large fungi similar in shape to mushrooms but unlike mushrooms are unsafe to eat. Some toadstools just have a very unpleasant taste, eating others causes nausea whilst eating some types can result in a severe or even fatal case of food poisoning.

Total count test:

The total count (or plate count) test is used to work out the total number of microbes in 1ml of milk. The legal limit is 20,0000 microbes per ml of pasteurised milk. Generally the lower the total count, the better the keeping quality of the pasteurised milk.

See pasteurisation.


A toxin is a poison (normally protein in nature) produced by a living entity. Most cases of microbial food poisoning are due to toxins. The toxin may be present and dangerous even though all the microbes which produced it are dead.

See food poisoning and bacteria.

Trade catering:

Trade catering means selling meals and snacks in order to make a profit. Examples of trade catering are restaurants and takeaways.

See service catering.


U.H.T. milk:

U.H.T. or Ultra High Temperature milk is a type of sterilised milk, in which the milk is heated to 133ºC for one second. This is done either by direct injection of steam or indirectly by using heat exchangers. The milk is aseptically packed into either plastic bottles or cartons.

See aseptic conditions, heat exchanger and sterilisation (milk).

Unfit food:

Unfit food is food which is unsafe to eat either because it is contaminated or because it is decomposing. Food which is passed its shelf life, i.e. 'Use By' or 'Best Before' date is deemed unfit. It is an offence (Warning UK only) to have unfit food on food premises unless the unfit food is clearly in a refuse container.

See contamination.

Use By:

A 'Use By' date needs to be applied to all high risk and rapidly perishable food even if stored under the appropriate conditions. No food should be sold, stored or eaten beyond its 'Use By' date.

See high risk food.


Vacuum packing:

Vacuum packing is a similar process to canning but laminated plastic or nylon pouches are used instead of tin cans. The vacuum packs can be sterilised after they have been heat sealed or the food can be sterilised then aseptically filled into vacuum packs which are then aseptically heat sealed. The pouches are usually sterilised by radiation before being aseptically filled.

See aseptic conditions, canning and sterilisation.



Water is a colourless, odourless, tasteless liquid which is essential for all life. It is composed of two elements: hydrogen and oxygen. Water is used as a solvent for most cleaning agents and hot water or steam is used as a disinfectant or sterilising agent.

See bound water, disinfection, free water and sterilisation.


The whey is the part of the milk which stays in solution after the curd has been separated out, when making cheese. The whey consists mainly of water but contains some proteins, sugars, fats and salt.

See curd.


Wholesome is a term used to describe food which is safe and nutritious. Sometimes the term wholesome is used to describe fresh food which is free from additives and preservatives, whilst other people use the term in contrast to junk food. However as far as the food hygienist is concerned wholesome means safe, nutritious and of high quality.

See additives and preservatives.



Yeasts are small unicellular fungi which reproduce by budding and spore formation. Under the microscope yeasts are a lot larger than bacteria. Yeasts are not known to cause food poisoning but they spoil liquid foods such as fruit juices, wines and beers.

See fungi, microbes and moulds.


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