Frozen food

Freezing food keeps it fresh from the time it is prepared until it is eaten. For a 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). The cold temperature keeps 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 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 tried freezing things like orange juice and vegetables.

Technology

Freezing food has become faster, easier, and cheaper 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 be strong for filling, sealing, freezing, storing, moving, thawing, and cooking. Many frozen foods are heated in a microwave oven, so some packaging can go straight from the freezer to the microwave.

In 1974, the first special container called a differential heating container (DHC) was made. This metal sleeve helped frozen foods get the right heat. Different sized openings 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 are always looking for new ways to improve frozen food packaging. Active packaging can help keep food safe and fresh 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
• Flavor enhancers
• Odor generators
• Oxygen-permeable films
• Oxygen generators

Effects on nutrients

Freezing food helps keep most of its nutrients. Only a little bit of vitamins may be lost. This makes frozen food a healthy choice. Some frozen meals might have extra salt and fats, so 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 loss happens during cleaning and cooling, not 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 slows down the growth of germs that make food go bad. When food is frozen, these germs can’t grow as fast.

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 frozen foods need to be defrosted before eating. Some frozen meats should be defrosted before cooking so they cook evenly and taste good.

There are 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. After defrosting, cook the food right away or throw it away if you don’t use it.

Quality

When food is frozen quickly, it makes tiny ice crystals. When it is frozen slowly, it makes bigger ice crystals. Bigger ice crystals can break the cells in the food. This can change how the food feels when you eat it and might make it lose its juices when it is thawed.

Different ways of freezing, like using machines with air or 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 showed that a person in America eats frozen food about 71 times a year. Most of these are meals that were cooked and then frozen.