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