The term "vegetable" generally refers to edible parts of plants. The definition of the word is traditional rather than scientific, and is somewhat arbitrary and subjective, as it is determined by individual cultural customs of cooking and food preparation.
Generally speaking, herbaceous plant or plant part which is regularly eaten as unsweetened or salted food by humans is considered to be a vegetable. Mushrooms, though belonging to the biological kingdom Fungi, are also generally considered to be vegetables, at least in the retail industry. Nuts, seeds, grains, herbs, spices and culinary fruits (see below), are usually not considered to be vegetables, even though they are all parts of plants. (There are of course numerous exceptions to this, including tomatoes, corn, etc.) In general, vegetables are regarded by cooks as being suitable for savory or salted dishes, rather than sweet dishes, although there are many exceptions, such as pumpkin pie Some vegetables, such as carrots, bell peppers and celery, are eaten either raw or cooked; while others, such as potato, are traditionally eaten only when cooked.
Frozen vegetables are commercially packaged vegetables that are sold in the frozen section of the store usually packaged in either rectangular boxes or plastic bags.
Common frozen vegetables include spinach, broccoli, cauliflower, peas, corn, Soya bean, green beans etc . They may be cut or processed some other way into a shape or form that is convenient for cooking or eating, and sometimes seasoned
Frozen vegetables have some advantages over fresh ones, in that they are available when the fresh counterpart is out-of-season, they have a practically infinite shelf life when kept in a freezer and that they often have been processed a step or more closer to eating. In many cases, they may be more economical to purchase than their fresh counterparts since they are already cooked, and will likely be cooked more once they enter the household, they are believed to be more sanitary than fresh vegetables.
The production process of frozen vegetables includes harvesting (picking), sorting, washing, cutting, blanching, packing and freezing.
The technology of frozen vegetables oriented itself in three directions:
1. The chemical and physical reactions which take place during the freezing process;
2. Scientific knowledge of the effect of freezing on the tissues of fruits and vegetables; and
3. Food microbiology.
1. The Chemical and Physical Reaction
Enzymes in vegetables are inactivated by the blanching process. Blanching is the exposure of the vegetables to boiling water or steam for a short period of time. The vegetable must then be rapidly cooled in ice water to prevent it from cooking, in most cases blanching is absolutely essential for producing quality frozen vegetables. Blanching also helps to destroy microorganisms on the surface of the vegetable and to make some vegetables, such as broccoli and spinach, more compact.
2. Effect of Freezing on Tissue
Vegetables should be frozen at 0° F or lower for 24 hour before distribution. Water makes up over 90 percent of the weight of most fruits and vegetables. This water and other chemical substances are held within the fairly rigid cell walls which give support structure, and texture to the fruit or vegetable. Freezing fruits and vegetables actually consists of freezing the water contained in the plant cells.
When the water freezes, it expands and the ice crystals cause the cell walls to rupture. Consequently, the texture of the produce, when thawed, will be much softer than it was when raw. This textural difference is especially noticeable in products which are usually consumed raw. For example, when a frozen tomato is thawed, it becomes mushy and watery. This explains why celery, lettuce, and tomatoes are not usually frozen and is the reason for the suggestion that frozen fruits, usually consumed raw, be served before they have completely thawed. In the partially thawed state, the effect of freezing on the vegetable tissue is less noticeable. The extent of cell wall rupture can be controlled by freezing produce as quickly as possible. In rapid freezing the technology currently employed is the IQF (individually quick frozen ) by chilled blast of air .
3. The Microbiology
The freezing process does not actually destroy the microorganisms which may be present on fruits and vegetables. While blanching destroys some microorganisms and there is a gradual decline in the number of these microorganisms during freezer storage, sufficient populations are still present to multiply in numbers and cause spoilage of the product when it thaws. For this reason it is necessary to carefully inspect any frozen products which have accidentally thawed by the freezer going off or the freezer door being left open.
4. Packing
There are two basic methods for packing vegetables for freezing, the tray pack and the dry pack.
Dry pack—This is the method used to describe the packing of blanched and drained vegetables into containers or freezer bags. Pack the vegetables tightly to cut down on the amount of air in the container. If the vegetables are packed in freezer bags, press air out of the unfilled part of the bag. When packing broccoli, alternate the heads and stems.
Tray Pack—this is the method of freezing individual pieces of blanched and drained vegetables on a tray or shallow pan, then packing the frozen pieces into a freezer bag or container. This method produces a product similar to commercially frozen plastic bags of individual vegetable pieces and is particularly good for peas, corn, and beans.
In this method it is most important to pack the individually frozen pieces into a bag or container as soon as they are frozen.
The technology to employed does not have any negative environmental impact.