LINDA LIPTAK'S new avocation adds her to the growing number of home gardeners who want to give their families repectable vegetables even in January, when red-ripe tomatoes can only be found in picture books.

The tomatoes, peppers, corn, beans, onions, cabbage, cantaloupe, watermelon, cucumbers, lettuce, spinach, zucchini and popcorn that are just beginning to sprout in her Burke, Va., back yard will not be left to fertilize the ground for next year's harvest.

Unlike other neigborhood gardeners, she will put to use the instruction she received at a recent four-day Virginia Cooperative Extension Service workshop that showed her how to freeze, can, dry and pickle food--not only in her own kitchen but as a volunteer for the extension service.

"I took the workshop because I wanted an expert's opinion," she explained, adding that she had never done any preserving before. "I was impressed by the course. If there was something I didn't understand, I just asked an agent and they gave me an answer."

By the workshop's end, Liptak, along with many of the other 30 volunteers from Arlington, Alexandria, Fairfax, Prince William and Loudoun counties were "ready for more. They kept us busy and interested," she said. "I feel more confident about doing home preserving now."

In return for her four days of free preserving lessons, Liptak and other class participants have agreed to donate their time to assist their county extension agents. In addition to answering the Northern Virgina Hotline (phone numbers appear in listing at left)--a service designed to help people get quick answers to their preserving questions during the summer gardening season--volunteers will lead mini-workshops in See WORKSHOPS, E17, Col. 1 Taking the Pressure Off WORKSHOPS, From E1 private homes, judge at county fairs and conduct safety tests on canning equipment.

During one six-hour lesson, the group learned drying and canning techniques (see related stories). In addition, participants discussed food quality and palatability, including the crucial topic of food spoilage.

"There are two kinds of food spoilage," said JoAnne Barton, a foods and nutrition extension specialist. "That which affects the palatability and aesthetics, such as sour milk and brown bananas, and microorganisms, the live growth that is not visible to the naked eye."

Though mold, yeast and enzymes affect the palatability and aesthetics of food, she said, they are not harmful. It is the microorganisms which are dangerous.

"Molds will grow on most anything--shoes, purses, showers and food." Small amounts can be scraped off food with a spoon and the food then eaten. Others which grow on peanuts, wheat and corn, however, can produce a toxin called aflatoxin that can be carcinogenic, she warned.

Yeast is stimulated by heat which causes fermentation and thus gas bubbles.. "You can see it happening," she said. "It's just unappetizing."

Enzymes cause ripening or darkening in foods such as peaches and apple slices. "It has nothing to do with food safety, and it will not endanger the health of your family," she said. This enzyme action can be stopped by using an anti-darkening agent such as Fruit Fresh, ACM, plain lemon or orange juice, ascorbic acid or vinegar and water. "Enzymes," she added, "need oxygen in order to work," which is why you keep foods that darken under a syrup.

Molds, yeasts, enzymes and certain bacteria cannot grow in high-acid foods (most commonly fruits) processed without pressure in a water-bath canner. But low-acid foods (usually vegetables) do not inhibit the growth of Clostridium botulinum, which produces the deadly botulism toxin. These bacteria can only be destroyed with the high heat obtained in a pressure canner, Barton said.

Botulism spores are produced in the food while it is still in the ground, she explained. However, they require three conditions in order to grow: moisture, an absence of oxygen and low-acid conditions. "A sealed jar of food is an ideal place for spores to grow and produce the toxin," Barton said.

"Since it's such a potent toxin you must use a very high temperature to kill it--10 pounds in a pressure canner causes the internal temperature of food to reach 240 degrees." Without pressure, water only reaches 212 degrees, she stressed. For this reason, all low-acid foods require processing in a pressure canner, while fruits, tomatoes, pickles and jams (high-acid foods) only need water-bath canning. The spores can also be destroyed by boiling food for 10 minutes before serving, but this destroys vitamins, too, and overcooks the food.

On the other hand, Barton said, there is little danger of food spoiling as it dries, because all the moisture is removed. "The biggest problem with drying is the possibility of mold growth. But you can see that," she said.

Food drying caught the eye of Lindsey Davis, a security policeman who grows "just about every little thing but corn" in his two Alexandria gardens.

"My grandparents sun-dried lots of things--corn, potatoes, peas," he said, but they never taught him the technique. So Davis decided to attend the workshop to learn how to dry and to get more up-to-date technology for his wife, who does the all the canning in their family.

Since the humidity in the Washington area makes sun drying a chancy venture, extension agents here don't recommend the technique to preservers. They do, however, offer advice about oven and dehydrator techniques.

"You dry," said cooking instructor and special guest lecturer Pat Worthington, "because it is economical--nutritionally and financially."

Drying "concentrates" all the nutrition into a smaller space, she said. "With canning you add water, so you're diluting." In addition, "most dehydrators on the market today cost 25 to 50 cents a day to run for 24 hours. It costs far less than freezing because you eliminate the cost of maintaining a freezer."

Finally, she said, drying food is not labor-intensive. You simply slice the fruit or vegetables, put them in the dehydrator and walk away, whereas the canning process demands the cook's attention from start to finish.

But even Worthington agrees that drying does not totally eliminate the need for canning. Canned tomatoes are here to stay, the workshop participants agreed, and following the demonstration, many said that they still preferred canning to drying.

Although Liptak said she found the drying workshop interesting, she probably won't dry her own produce. "The end result just doesn't appeal to me. I just don't care for the dried fruits and vegetables as much, and you have to spend more money on the equipment."

On the other hand, Davis said he likes drying the best, adding that if he can find affordable equipment, he will use the technique in the future.

Whatever preserving method the volunteers liked best, they had the opportunity to try their hands at each during the four-day workshop. Jelly-making, drying and canning, freezing and pickling were all discussed and demonstrated. Mistakes occurred, but extension agents used them to illustrate the importance of following directions.

"What we learned, of course, is the perfect way of canning and freezing," said Liptak of the seminars. "When you talk to people who have been doing it for years, they say 'oh, you don't have to do that.' Now I just tell them, 'well there can be problems.' We cook differently today than your grandmother did."