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The Science Behind Freezing


Freezing is used as a preservation method for almost all foods. From fruits and vegetables to meat and seafood, freezing is a popular way to keep food fresh after harvesting. With an extended shelf life and more nutrients, frozen products are frozen when they have the most minerals and vitamins. However, what exactly happens when food is being frozen?

Chemical Changes

We all know that fruits and vegetables start to deteriorate right when they are harvested. Freezing happens right after harvesting to seal in the taste and texture of the product at its peak degree of ripeness. However, the chemistry behind this is a little more complicated. Fresh produce contains enzymes, which cause the loss of color, loss of nutrients, flavor changes, and color changes. These enzymes have to be inactivated to prevent these reactions.

For vegetables, enzymes are inactivated with blanching. Blanching exposes vegetables to boiling water or steam for a short period of time. Then the vegetable is rapidly cooled in ice water to prevent it from cooking. Blanching also helps destroy microorganisms on the surface of the vegetable and it makes some vegetables, like broccoli, more compact.

With fruit, the enzymes cause brown colors and a loss of vitamin C. Because fruits are normally served raw, they can’t be blanched like vegetables. Instead, these enzymes are controlled with chemical compounds that interfere with the enzymes. Ascorbic acid, vitamin C, is the most popular chemical used and can be used in its pure form or mixed with sugar. Soaking in dilute vinegar and a coating of sugar and lemon juice is another option.

Textural Changes

With fruits and vegetables, the textural changes have to do with water. Water makes up 70-90% of the weight of most fruits and vegetables. It and other substances are stored in the rigid cell walls which support the structure and texture of the product. When you freeze a fruit or vegetable, you are freezing the water contained in the cells. As the water freezes, it expands, and ice crystals cause the cells walls to rupture. This causes the texture to be much softer when it is thawed than when it was raw. This is why some vegetables, like celery and lettuce, are not usually frozen. In order to control the extent of cell wall rupture, you have to freeze the produce as quickly as possible. With rapid freezing, a large number of small ice crystals form compared to slow freezing which forms fewer larger crystals.Because of the soft texture when thawed, most frozen fruits are served when they are not completely thawed. In a partially thawed state, the effects of freezing are less noticeable. It is also less noticeable for products that are cooked before eating because cooking also softens cell walls.

Individual Quick Freezing

Don’t go for the one-size-fits-all approach. Individual Quick Freezing is the ideal choice for high-value produce. Your produce will maintain its natural appearance, texture, and color when frozen in an IQF Tunnel. An IQF Tunnel will not only lock in nutrients but also ensure the highest quality product that can be sold at a premium price. At AFE each piece of equipment is crafted with full dedication to hygiene, quality, and cleanliness. Fully Welded Stainless Steel enclosures will ensure the highest degree of sanitation in the industry and long-term durability.  Cleanliness and hygiene are critical considerations when it comes to food processing and preservation. Our IQF Tunnels can be fabricated using fully welded stainless steel panels or stainless steel clad panels that provide exceptional sanitation and durability. Each piece far exceeds the industry standards for health, cleanliness, and energy savings to give you the best results for your business. For any of your freezing needs, look to AFE for a wide variety of freezer and cooler products.