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Dried-Vegetables

Page history last edited by Jacqui 9 years, 10 months ago

 

Author: Subash Shrestha, Utah State Univ.

 

Storing Dried Vegetables

 

Introduction

Keeping out air and moisture from dried foods is the secret for successful storage. To maintain the quality and safety of home dried vegetables, you'll need to take special care when packaging and storing them.

 

Quality and Purchase

Freeze dried vegetables are superior to other mechanical/home dried for storage. Freeze-drying uses low heat and causes little damage to the tissue, taste or aroma. Products easily restore and closely resemble the taste, texture, and nutritional content of the original food. In sun drying or in mechanical drying, the cell walls are often damaged and the essential flavor and texture of the food is lost during evaporation of water. The extent of loss depends upon the type of drying method and the expertise in controlling other drying parameters. Commercial dryers can closely control quality and safety to produce the best product. Commercially dried vegetables can be purchased at grocery stores and similar outlets. Check the labels for the freshness of the dried product at the time of buying.

Vegetables selected for drying should be sound, fresh, and in the "peak" of condition; ripe, but still firm and at the right state of maturity. Vegetables that are inferior before drying will be inferior after drying. Wilted or inferior material will not make a satisfactory product. Immature vegetable will be weak in color and flavor. Over-mature vegetables are usually tough and woody. Over-mature or bruised ones are likely to spoil before the drying process can be accomplished.

Even when you're using an oven or an electric dehydrator, you'll have to watch out for the effects of humidity on drying foods. Choose a bright, sunny day for your home drying—that way you'll keep the dried vegetables from picking up moisture from the surrounding air after they leave the oven or dryer. The science based procedure for home drying of most vegetables can be found in http://extension.usu.edu/files/publications/publication/FN-330.pdf

 

Packaging

Dried foods are susceptible to insect contamination and moisture absorption and must be properly packaged and stored immediately. First, cool (condition) completely. Conditioning is an important safety measure because packaging warm food causes sweating, which could provide enough moisture for mold to grow. Pack foods into clean, dry, insect-proof containers as tightly as possible without crushing (b). If possible, pack the foods in amount that can be used after opening the package without requiring further repackaging and storage.

Glass jars (preferably dark colored), metal cans or boxes with tightly fitted lids or moisture- and vapor-resistant freezer cartons make good containers for storing dried foods. Heavy-duty plastic bags are acceptable but are not insect- and rodent-proof (b). To protect from insects and re-absorption of moisture, seal lids onto containers. Wrap the edge where the lid meets the container with a plasticized, pressure-sensitive tape or clean, 1-inch cloth strip dipped in melted paraffin. Bags may be heat-sealed or closed with twist ties, string or rubber bands. Label containers with the name of the product, date, and method of pretreatment and drying (e). Oxygen absorbers should be used to remove oxygen from the packages to extend shelf life and minimize off-flavors.

 

Storage Conditions

Containers of dried vegetables should be stored in a dry, cool, dark place away from furnaces. Low storage temperatures extend the shelf life of dried products. Always store metal cans off of the floor, especially bare concrete. Moisture can wick up to cans and encourage rusting (h). If there is enough space in freezer, dried vegetables can also be stored in freezer to enhance the shelf life.

Foods that are packaged seemingly bone-dry can spoil if moisture is reabsorbed during storage. Check dried foods frequently during storage to see if they are still dry. Glass containers are excellent for storage because any moisture that collects on the inside can be seen easily. Foods affected by moisture, but not spoiled, should be used immediately or redried and repackaged. Moldy foods should be discarded (b).

Properly stored, dried vegetables keep well for six to 12 months. Discard all foods that develop off smells or flavors or show signs of mold.

 

Nutrition and Allergies

Drying, like all methods of preservation, can result in loss of some nutrients. Nutritional changes that occur during drying include (e):

• Calorie content: does not change, but is concentrated into a smaller mass as moisture is removed.

• Fiber: no change.

• Vitamin A: fairly well retained under controlled heat methods.

• Vitamin C: mostly destroyed during blanching and drying of vegetables.

• Thiamin, riboflavin, niacin: some loss during blanching but fairly good retention if the water used to rehydrate also is consumed.

• Minerals: some may be lost during rehydration if soaking water is not used. Iron is not destroyed by drying.

Blanching vegetables (to destroy enzymes) before freezing and drying reduces the amount of heat-sensitive and water soluble vitamins to some degree. There could be some nutrient loss if canned and dried food is stored at high temperatures (d). A research article in American Journal of Food Technology ( c ) reported that ascorbic acid (Vitamin C) reduced to half in leafy vegetables as a result of drying but storage for twelve weeks in polyethylene wrappers did not result into much further loss.

Light destroys the vitamin A and C content during storage. It can be prevented by use of dark colored or opaque container. One typical change that occurs during storage is “Maillard Browning” which involves complex chemical reactions between the food’s sugar and protein. Other changes include general discoloration (f).

 

Shelf Life

All dried vegetables deteriorate to some extent during storage, losing vitamins, flavor, color and aroma. For this reason, dried vegetables will not retain their appeal indefinitely. Carrots, onions and cabbages deteriorate more quickly than other vegetables, and will generally have a shelf life of only 6 months (a). Recommended storage time for dried foods range from four months to one year. Because food quality is affected by heat, the storage temperature helps determine the length of storage; the higher the temperature, the shorter the storage time. Vegetables have about half the shelf-life of fruits, and can generally be stored for six months at 60 F or three months at 80 F (b). The sensory shelf life of dehydrated potato flakes packaged in nr 10 cans held at ambient temperatures was found to be 16 yr (g).

 

Use from Storage

When you open the jar, smell the contents and discard any vegetables that have an odd odor. In addition, do a quick visual inspection and discard any that show signs of mold.

One cup of dried vegetables reconstitutes to about 2 cups (e). Most vegetables are soaked or rehydrated in cold water prior to use. Add sufficient water to keep them covered. After soaking, simmer until desired tenderness. There are two other acceptable rehydration methods: adding the dried product to hot/boiling water or adding the dried vegetable to a product with lots of liquid, such as soup. Whichever rehydration method is chosen, the vegetables return to their original shape. Vegetables can be soaked in either water or, for additional flavor, bouillon or vegetable juice. They usually rehydrate within one to two hours. If they are soaked for more than two hours, or overnight, they should be refrigerated. Using hot/boiling liquid speeds up the soaking process. Save and use the soaking liquid in cooking. Adding dried vegetables directly to soups and stews is the simplest way to rehydrate vegetables. Leafy vegetables, cabbage and tomatoes do not need to be soaked (b).

 

References

a. http://web1.msue.msu.edu/imp/mod01/01600522.html#TOC

b. http://hgic.clemson.edu/factsheets/HGIC3085.htm

c. http://www.scialert.net/xml/ajft/0000/3032-3032-full.xml

d. http://extension.oregonstate.edu/nep/Reports/fruit_veg_summit/what_counts_fact_sheet.pdf

e. http://www.ext.colostate.edu/PUBS/FOODNUT/09308.html

f. http://www.scribd.com/doc/8078858/Drying-Fruits-Vegetables-Nutrition

g. Neilson AP, Pahulu HF, Ogden LV, Pike OA. "Sensory and nutritional quality of dehydrated potato flakes in long-term storage." Journal of Food Science. 71.6 (2006): S461-S466.

h. http://extension.usu.edu/foodstorage/htm/canned-goods

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