Frozen food

Freezing food keeps it fresh from the time it is prepared until it is eaten. For a very long time, farmers, fishermen, and trappers have kept grains and produce safe by storing them in unheated buildings during winter. Freezing slows down the process that makes food go bad by turning the water inside it into ice, which stops most germs from growing.

In factories, there are two ways to freeze food: using machines or using very cold air, also called flash freezing. How fast the food is frozen is very important to keep its quality and texture. Freezing very quickly makes tiny ice crystals that help keep the food's natural structure.

Today, people use freezers in their homes to keep food fresh. Experts suggest freezing food on the day it is bought. In 2012, a group of supermarkets in the United Kingdom started a campaign to encourage people to freeze food as soon as possible, but not after the "use by" date on the package. This advice was supported by the Food Standards Agency, as long as the food had been stored properly before freezing.

Preservatives

Frozen foods don’t need extra preservatives because tiny living things like microorganisms can’t grow when the food is kept very cold, below −9.5 °C (15 °F). This cold temperature helps keep the food fresh without any extra ingredients. Sometimes, a substance called carboxymethylcellulose (CMC) is added to frozen food. It’s a stabilizer that has no taste or smell and doesn’t change the quality of the food. For keeping food fresh for a very long time, even colder temperatures might be needed.

History

People in cold places have used natural freezing, like winter frosts, to keep food fresh for a long time.

In 1861, a man named Thomas Sutcliffe Mort set up the first freezing factory in Sydney, Australia. He worked with an engineer named Eugene Dominic Nicolle. In 1868, they sent the first frozen meat to London. Later, frozen meat shipments from Australia and New Zealand to Europe began in 1881. By 1899, frozen chickens and geese were being sent from Russia to London.

In 1929, Clarence Birdseye brought "flash freezing" to the United States. He got the idea from seeing how people in Labrador and the Inuit in Canada used natural freezing to keep food. In 1934, Iceland started helping fishermen freeze their fish. During World War II, the military also tried freezing things like orange juice and vegetables.

Technology

Freezing food has become faster, more efficient, and less expensive over time. One way to freeze food quickly is by using very cold liquids, like liquid nitrogen. This method is often used for fish, seafood, fruits, and berries, but it can be costly.

Most frozen food is frozen using machines that cool the air, similar to regular freezers. While this method is cheaper for large amounts of food, it is usually slower. There are many ways to make this process faster, such as blowing cold air over the food or using cold metal plates to freeze it.

Some methods include:

• Air-blast freezing, where food is placed in a cold room with air blown over it.
• Belt freezers, which use a conveyor belt inside a cold room.
• Tunnel freezing, where food moves on racks through a tunnel of cold air.
• Fluidized bed freezing, where small pieces of food are blown by fast-moving cold air for quick freezing.

Other methods use direct contact with cold surfaces or liquids to freeze the food faster. These include plate freezing, where food is pressed between cold metal plates, and immersion freezing, where food is dipped into a very cold liquid.

Individual quick freezing is a term for any freezing method that freezes food quickly and individually, not in large blocks.

Packaging

Frozen food packaging needs to stay strong during filling, sealing, freezing, storage, moving, thawing, and even cooking. Since many frozen foods are heated in a microwave oven, special packaging can go straight from the freezer to the microwave.

In 1974, the first special container called a differential heating container (DHC) was made for the public. This metal sleeve helped frozen foods get the right amount of heat. Different sized openings around the sleeve let people choose how much heat their frozen dinner needed.

Today, there are many choices for frozen food packaging, like boxes, cartons, bags, pouches, boil-in-bags, lidded trays and pans, crystallized PET trays, and plastic cans.

Scientists keep studying new ways to improve frozen food packaging. Active packaging can sense and remove harmful things, helping keep food safe and fresh for longer. Some new ideas being studied include:

• Oxygen scavengers
• Time temperature indicators and digital temperature data loggers
• Antimicrobials
• Carbon dioxide controllers
• Microwave susceptors
• Moisture control: water activity, moisture vapor transmission rate, etc.
• Flavor enhancers
• Odor generators
• Oxygen-permeable films
• Oxygen generators

Effects on nutrients

Freezing food helps keep most of its nutrients, with only small amounts of vitamins being lost. This makes frozen food a good and healthy choice compared to fresh food. However, some frozen meals may have extra salt and fats added, so it’s a good idea to check the nutrition label and ingredients list.

Vitamin content of frozen fruits and vegetables

• Vitamin C: This vitamin is often lost more than others. Most of the loss happens during cleaning and cooling, not during freezing.
• Vitamin B₁ (thiamin): About 25% of this vitamin may be lost. It dissolves easily in water and can be destroyed by heat.
• Vitamin B₂ (riboflavin): There isn’t much research on how freezing affects this vitamin. Some studies show small losses, but it’s thought that losses happen during preparation, not freezing.
• Vitamin A (carotene): Very little of this vitamin is lost during freezing. Most loss happens during long storage times.

Effectiveness

Freezing is a good way to keep food fresh. It works by slowing down the growth of germs that make food go bad. When food is frozen, these germs can’t grow as fast, but they might not be completely stopped.

Food can stay good in the freezer for many months if kept at a very cold temperature of −18 °C (0 °F) or colder. This helps make sure we have food available even when it’s not in season.

Defrosting

Many foods that have been frozen need to be defrosted before we eat them. Some frozen meats should be defrosted before cooking to make sure they cook evenly and taste good.

There are several safe ways to defrost food:

• in a refrigerator
• in a microwave oven
• wrapped in plastic and placed in cold water or under cold running water

It’s best to avoid leaving food at room temperature because it can be unsafe to eat. After defrosting, cook the food right away or throw it away if you don’t use it.

Quality

When food is frozen quickly, it forms many small ice crystals. When it is frozen slowly, it forms fewer but larger ice crystals. The size of these ice crystals matters because larger ones can break the cells in the food. This can change how the food feels when you eat it and might cause it to lose its juices when it is thawed.

Different ways of freezing, like using machines with air or using very cold liquid nitrogen, can change the size of the ice crystals and affect the quality of the frozen food.

Reaction

A study from 2007 found that, on average, a person in America eats frozen food about 71 times each year. Most of these are meals that have already been cooked and then frozen.