food commodities, processing and hygiene key terms

sensible heat

the amount of energy needed to change the temperature of a substance of product without changing the phase of it.

latent heat

energy needed to change the state/phase of a substance

chilling

reducing temperature to the desired holding temperature just above the freezing point of the food.

time temperature indicators

These are labels with a dye (or mixture of dyes) that change colour according to a chemical reaction affected by compounds and/or temperature.

evaporator function in fridge

cold liquid absorbs heat from air in the fridge, chilling the inside of the fridge, the liquid vaporises

compressor function in the fridge

vapour is compressed bringing it to a higher temperature

condenser function in fridge

gas cools and liquifies, releasing heat through the ventilation fins on the back of the fridge. As heat is removed gas is condensed to a liquid

expansion valve function in fridge

flow if liquid is controlled and pressure is lowered so that some of the liquid turns to vapour, evaporation cools the remaining liquid

freezing point of food

temperature at which ice crystals exist in equilibrium with the surrounding water

eutectic temperature

temperature where a crystal of an individual solute exists in equilibrium with the unfrozen liquor and ice

blast freezer

rapidly circulates very cold air to freeze rapidly

fluidised bed freezer

A type of freezer that uses a stream of cold air to suspend and freeze food particles uniformly.

immersion freezer

immerses food in a low temperature coolant

plate freezer

A type of freezer that utilises metal plates to freeze food items quickly and evenly, often used for large batches of products.

scraped surface freezer

A type of freezer that uses a scraping mechanism to continuously remove ice from the surface, ensuring even freezing and preventing product build-up.

cryogenic freezer

A freezer that employs cryogenic gases like liquid nitrogen to rapidly freeze food products, preserving quality and texture.

conduction

controls the transfer of heat through a solid mass or material, heat flows from hot zones to cold zones by vibrational energy between molecules

convention

heat flows from hot zones to cold zones by means of physical movement of fluids (liquid or gas)

natural convection

The process of heat transfer where fluid motion is caused by differences in temperature and density within the fluid, allowing warmer, less dense fluid to rise and cooler, denser fluid to sink.

forced convection

The transfer of heat in a fluid where external forces, such as fans or pumps, create movement, enhancing the heat transfer rate compared to natural convection.

radiation

The transfer of heat in the form of electromagnetic waves, such as infrared radiation, without the need for a medium to conduct the heat.

pasteurisation

thermal process designed to give a 5-6 log reduction in microorganisms and contamination levels

pasteurised milk

milk must be heated to at least 71.7˚C for 15 seconds or another combination with the equivalent effect

batch pasteurisation

63.8˚C for 30 minutes

viscosity

resistance to flowof a fluid, influenced by its temperature and composition.

Reynold’s number

a dimensionless number used to predict flow patterns in different fluid flow situations, determined by the ratio of inertial forces to viscous forces.

Reynold’s number equation

The mathematical formula used to calculate Reynold's number is expressed as Re = (density x velocity x characteristic length) / viscosity.

plate heat exchanger

banks of stainless steel plates with troughs and dimples designed to give turbulent flow. These heat exchangers are used for transferring heat between two fluids with high efficiency and compact design.

commercial sterility

the condition achieved by application of heat, alone or in combination with other treatments, to render food free from microorganisms capable of growing in food at temperatures at which the food is likely to be held in manufacture, distribution and storage.

canning

>3 minutes at 121.1˚C or equivalent to achieve a 12 log reduction in spores of Clostridium botulinum and ensure commercial sterility in preserved foods.

aseptic processing and packaging

a process in which the product and container are separately sterilised and then combined under commercially sterile conditions

sensible heat

the amount of heat required to change the temperature of a substance without changing its state.

latent heat

the heat absorbed or released by a substance during a change of state without changing its temperature.

drying

removal of water from food

air and contact drying under atmospheric pressure

heat is transferred through the food either from heated air or from heated surfaces, the water vapour is removed in the air

vacuum drying

heat transfer by conduction in a vacuum environment, reducing water's boiling point and promoting faster drying.

freeze drying

Water vapour is sublimed off frozen food, maintaining the food structure

3 phases of air drying

tray dryers, tunnel dryers, vacuum dryers

tray dryers

Heating may be an air current sweeping across the trays, by conduction from heated trays or heated shelves that the trays are on or by radiation from heated surfaces.

tunnel dryers

trays on trolleys move through a tunnel where heat is applied by air (parallel or countercurrent) and vapours removed

vacuum dryer

similar to tray dryers but operater under a vacuum and heat transfer is by conduction or radiation

roller or drum dryers

food is spread over the surface of a heated drum (heated by steam), the drum rotates as the food dries and and is then scraped off at the end

fluidised bed dryer

food is maintained suspended against gravity in an upward flowing air stream, there may be horizontal air to move food through the dryer, heat is transferred from the air and to the food material by convection

rotary dryer

food is contained in a horizontal inclined cylinder that it travels through being heated by air flow or conduction of heat from the cylinder walls, either the cylinder rotates or there is a paddle or screw that rotates within the cylinder

spray dryer

used for foods that may be affected by heat. liquid or fine solid material in a slurry is sprayed in the form of a fine droplet dispersion into a current of heated air. drying occurs very rapidly.

freeze dryer

material is held on shelves or belts in a chamber under a high vacuum, food is usually frozen before drying, heat is transferred to the food by conduction or radiation and the vapour is removed by a vacuum pump

trough dryer

materials are contained in a trough shaped mesh conveyor belt and air is blown through the bed of material, the movement of the conveyor continually turns over the material exposing fresh surfaces to hot air

bin dryers

the food is contained in a bin with a perforated bottom, warm air is blown vertically upwards, passing through the material

belt dryer

food is spread as a thin layer on a horizontal mesh or solid belt and air passes through or over the material, usually the belt moves but sometimes material is moved by scrapers

objective of mixing

to obtain a uniform mixture from 2 or more components by dispersing one within the others

tumbling mixer

rotate powders as they flow through a mixer to mix, speed of the mixer is optimied for the blend of ingredients , internal baffles or counter rotating arms can be used to improve mixing

critical speed of mixing

centrifugal force exceeds gravity and mixing ceases

screw type mixer

either U-trough/ribbon or vertical screw mixer designed to continuously mix materials using helical screw flights that transport and blend the ingredients throughout the mixer, used for dry or particulate solids

paddle agitator

A device used to mix liquids or slurries by means of blades or paddles that rotate to create turbulence and promote mixing.

multiple paddle agitator

A mixing device featuring several paddles that rotate simultaneously to enhance mixing efficiency and promote uniformity in liquids or slurries.

turbine agitator

A mixing device that uses a series of blades or discs to create high-shear mixing and effective fluid motion in various materials, often used for emulsifying or dispersing solids in liquids.

anchor and gate paddle

A type of mixer designed with a stationary anchor and rotating paddles, used to mix viscous materials effectively by minimizing product sticking and improving shear.

planetary/orbital mixer

A type of mixer that moves in a planetary motion, allowing for thorough mixing of ingredients, particularly in dough or thick mixtures, by combining rotational and orbital movement.

intrinsic factors affecting microbial growth

properties if the food itself, water content, pH, availability of nutrients, availability of oxygen, presence of natural antimicrobials

extrinsic factors that affect microbial growth

environmental conditions around food, temperature, carbon dioxide

implicit factors that affect microbial growth

interactions between microorganisms, antagonism, synergism, succession

antagonism

a type of interaction where one microorganism inhibits the growth of another, often resulting in reduced competitiveness for resources.

synergism

a type of interaction where two or more microorganisms work together, enhancing each other's growth and activity, which can lead to greater efficiency in resource utilization.

succession

the process through which microbial communities change over time, often involving the replacement of one community by another, leading to shifts in species composition and functionality.

progressing factors that affect microbial growth

physical or chemical effects of food preservation of food preservation processes

sub lethal injury

refers to damage to microorganisms that does not kill them but impairs their ability to grow or reproduce, often resulting from environmental stresses like heat or chemicals. no recoverable on selective culture membrane but under suitable conditions may recover viability. retain their pathogenic traits

repair methods

methods to revive injured cells before plating

blanching

scalding veg in boiling water for a short time, destroys enzymes which can cause off orours and flavours, preserving colour and texture and helps maintain nutritional value.

pasteurisation

mild heat treatment at temperaturesof 60-100˚C, achieves a 5-7 log reduction in pathogenic organisms

thermal D value

time needed at a particular temperature to destroy 90% of the target microorganisms

heat sterilisation

foods heated to a sufficiently high temperature for a sufficiently long time to destroy all microbial activity

botulinum cook

121˚C for 3 minutes, to achieve a 12 log reduction in spores

extrusion

A food processing technique that forces ingredients through a shaped opening, resulting in a specific texture and shape, often used for cereals and snacks. hot extrusion reduced microbial load of a food

psychrophile

A microorganism that thrives at low temperatures, typically between 0˚C and 20˚C, and can spoil food in refrigeration.

psychrotroph

A microorganism that can grow at low temperatures, typically between 0˚C and 30˚C, and can spoil food stored in refrigeration.

mesophile

A microorganism that grows optimally at moderate temperatures, generally between 30˚C and 45˚C, and is commonly associated with food spoilage at room temperature.

thermophile

A microorganism that thrives at high temperatures, typically between 45˚C and 80˚C, and is often found in environments like hot springs.

ionising radiation

damages spoilage and pathogenic microorganisms found in food, radiation causes double or single strans break in the DNA of these organisms, leading to their inactivation or death.

hurdle technology

using a combination of several, less intensive preservation treatments to avoid the sensory and nutrient losses when using one harsh preservation method while ensuring the safety and shelf life of the food product.

grinding

reduction in size by fracturing - mechanical action puts the food under stress or strain

hammer mill (grinding)

swinging hammerheads attached to a rotor, used to pulverize materials into smaller particles.

roller mills (grinding)

both smooth and fluted rollers rotating at different speeds (used for flour)

plate mill (grinding)

2 circular plates, one fixed and the other rotating, material enters near the axis of rotation and is sheared and crushed as it makes its way to the edge of the plates

fixed head mills (grinding)

fixed casing and rotating head with fine clearance between them

ball mill (grinding)

material tumbled with large number of steel balls used for grinfding colourants

edge runner mill (grinding)

heavy broad wheel running around circular trough - used for grinding chocolate and confectionary

cutters

rotating knives in various arrangements

bowl chopper (cutter)

flat bowl with material chopped by revolving bekow a vertical cutting knife

atomisation

aa processing technique that involves converting a liquid into a fine s[ray or mist to facilitate drying or enhancement of food functionality

pressure nozzle

a type of atomiser that forces milk through a small office