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Nerdy Science in the Kitchen

Tips on Freezing Fresh Produce



We all freeze fruits and vegetables in fridges and freezers in our home in order to keep them fresh. However, just like most things in our lives, we don’t really pay attention to the intricacies or the science of freezing produce since it’s such a throwaway thing.

Assortment of Fruits and Vegetables

Freezing produce is a very technical process and getting it right can make the difference between eating great tasting fruits and vegetables and those that feel stale in your mouth. Here are a few instructions you can follow regarding freezing fruits and vegetables.

The Science of Freezing Produce

The basic things you need to know about freezing produce is that there are chemical and physical reactions that take place during the process. The scientific knowledge of these effects can help you freeze them better and help you achieve a better texture and taste.

Chemical Changes and How to Stop Them

After they’re harvested, fruits and vegetables continue to undergo chemical changes and these can cause them to spoil and deteriorate. This is why these products have to be frozen soon after and their peak degree of ripeness maintained.

Enzyme Action

The enzymes inside the fresh produce begin to act as soon as they’re harvested and they can cause a loss of nutrients and flavor changes as well as changes in color. These enzymes have to be deactivated so that these reactions are stalled.

To effectively freeze these vegetables and reduce damage from enzymes even while they’re frozen, you can use blanching. This is the process of boiling the vegetables in water or exposing them to steam for a very brief period of time. Then they need to be rapidly cooled in ice water so they’re prevented from being cooked.

This process is deemed essential for preparing vegetables for freezing. It also helps kill microorganisms that are on the surface of the vegetables.

Addition of Ascorbic Acid

You can also add ascorbic acid, or vitamin C in order to preserve these vegetables and fruits since the loss of it can allow for the development of brown colors. Thus adding vitamin C can help the aesthetics and the taste of the fruits and vegetables in question.

Less Effective Methods

There are other methods that can produce vegetable and fruits fit for preservation like treating them with dilute vinegar solutions or coating the fruits with sugar and lemon juice. The problem with these methods is that they don’t prevent browning as effectively as treatment with ascorbic acid.

Limiting Air

Another effective way of stopping enzyme reactions within produce is that you can limit air during freezing. If air is let in, then very rancid oxidative flavors can develop within the produce and can cause the taste to spoil.

You can use wrapping material that doesn’t allow air to pass into the produce and remove as much air from the freezer or refrigerator so that you can reduce the contact it has with the produce.

Textural Changes

Since water makes over 90% of the weight of most fruits and vegetables, this is very important in their preservation. This is why you see vegetable and fruit sellers often spraying their produce with water. This water and other chemical substances are held in the very rigid cell walls within the fruits and vegetables and they give structure and texture to the produce.

Freezing them actually consists of freezing the water contained in the plant cells.

Freezing and Thawing Makes Produce Softer

When the water inside the produce freezes, it actually expands and the ice crystals in the cell walls rupture the walls. This way, the texture of the produce is much softer when it is thawed than when it is raw. This difference in texture is very noticeable in products that are consumed raw.

For example, when the frozen tomato is thawed, it becomes mushy and watery. This explains why the celery and lettuce are not usually frozen and the reason for the suggestion that frozen fruits which are consumed raw should be serviced before they’ve completely thawed.

If they’ve been completely thawed, the effect of freezing on the fruit tissue isn’t as noticeable. In fact, textural changes caused by freezing aren’t as apparent in the products that are cooked before eating since cooking also softens cell walls. The changes are less noticeable since they are high in starch like peas and corn and lima beans.

Controlling the Rate of Freezing

In order to get the best texture and best taste for your produce, it’s advisable to freeze as quickly as possible. The extent of the cell wall rupture can be controlled by freezing the produce very quickly. Through this, a large number of small ice crystals are formed. These produce less cell wall rupture than if you slowly freeze the vegetables.

This is why home freezer manuals recommend that the temperature of the freezer be set as the coldest setting hours before the foods are to be placed in the freezer.

Don’t Overload the Freezer

All freezer manuals also give guidelines for the maximum number of cubic feet of unfrozen product that can be frozen at once. This is usually 2 to 3 pounds of vegetables to each cubic foot of freezer space per 24 hours. Overloading the freezer will also result in the unfrozen products freezing over a long time and forming very large ice crystals.

Freezing fresh produce is an art and a science combined. Freezing your produce using the tips above can give you delicious food, whereas doing so wrongly can give you very badly tasting produce that has browned and lost its luster.

Kitchen Professor author
About the Author: Rhonda Richardson, Editor

Rhonda grew up with parents who gardened, hunted, fished, canned, and preserved food. Her mother was a professional cook and Rhonda credits her teaching everything from how to make homemade biscuits and gravy to what kind of meals to serve for different occasions. In the kitchen, Rhonda uses a mix of old-fashioned country cooking and up-to-date fads in the kitchen, often experimenting with replacing higher-calorie or fat ingredients with healthier options that still retain the delicious flavors of the originals.

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