Before becoming a technician for refrigeration, it would make perfect sense to understand how fridges preserve food.

The definition of cold is the “lack” of heat as we explained earlier. The colder an object is, the slower the molecules move. In the case of food cooling in a fridge, the molecules move slowly, which makes organisms move sluggishly and reduce reproduction, but does not necessarily kill them. In some cases, organisms can become dormant.

Refrigeration also slows down the oxidation of food which reduces bacteria growth in cells and fibres found in food. It also reduces the evaporation of moisture from food, too much-released condensation, and promotes bacterial growth.

Understanding bacteria

Food needs to maintain a steady low temperature. As bacteria can rapidly grow on food which causes it to spoil, an optimum temperature is required to slow down this process of reproduction.

Important to remember is that we get sick or infected by bacteria because of the number of bacteria that enter our digestive systems. High numbers of bacteria overwhelm our immune system, therefore refrigerators help to minimise the infection rates by reducing the number of times bacteria can multiply/reproduce.

Bacteria can reproduce at a rate where it doubles every 20 minutes in temperatures between 5°C and 60°C (Danger zone).

In other words, if a piece of chicken has 4 single bacterial units, leaving it for 30 minutes or longer in the “danger zone,” then by the two-hour mark you will already have 256 germs. If you leave it sitting out for just one more hour, the number of bacteria will reach 4,096. This is why food should be refrigerated within 2 hours of cooking, prepping or storing.

Food Storage Temperatures

Refrigerators above 0°C slow down this bacterial growth to keep food longer, however, food eventually spoils after a few days because of enzymes in the food and sporadic bacteria that are still growing slowly.

In the case of freezers where the temperatures can range from -15°C to -18°C, they do not necessarily “kill” bacteria, instead they ultimately “freeze” bacteria into dormancy, which is why it is important to cook thawed food as soon as possible as it can spoil faster.

Food frozen near to freezing point can spoil and taste “funny” due to ice crystals breaking down colloids and tissues.

This is why food should either be kept cool at 1.7°C to 7.30°C for refrigeration, or preserved for long term at -15°C.

Food kept between 1°C and -10°C promotes ice crystals to form and grow in the food tissue, which can alter the taste considerably, or spoil food to be inedible.

Because refrigerators can dry the air, food must be kept in storage containers to preserve the moisture level in the container and to prevent cross-contamination with other foods.

Although a cold fridge or freezer slows down or kills bacteria, the food needs to be carefully placed in a refrigerator for hygienic purposes and preserve food longer, and minimise waste.

Ideal temperatures for beverages

Although there is no set rule for the chilling of beverages, however, there is one exception where the beer will retain a better taste without the bloating effect when it is kept at 4 to 7°C.

With the exception of brewed beverages, on average 4°C is the optimum temperature for cooldrinks, enough to keep customers satisfied

Also important to remember, is that glass bottles kept at freezing or below freezing could explode because liquid expands when frozen.

Correct refrigeration health and hygiene

Seal and close all produce

Storing uncooked meat

Storing fresh produce

Marinade can be dangerous!

Do not use door shelves for dairy

Follow the 2-Hour Rule

Allow food to cool before placing it in the fridge

Remove cardboard packaging

Fresh vegetables and produce should be in a crisper

Use “Date-Dots” on all produce

Never place raw and cooked meat in the same fridge without being sealed

Place raw food beneath cooked food

Freezing facts