When teen-agers do the grocery shopping they often come back with soft, chewy foods for the main meal and crunchy foods for between-meal snacks. An adult would probably choose different textures. So would older people or thin people. In food, there are as many differences in what textures we prefer as there are in taste and smell.
Cultural expectations, time of day, socioeconomic status, sex, age, weight - all play a role, says Susan Schiffman, professor of psychology, Duke University, speaking at the Annual Newspaper Food Editors Conference here.
Today's trend in eating fresh foods and cooking from scratch has brought about a focus on texture, or ''mouth feel.'' Current studies on the ''crispness'' and ''crunchiness'' of foods show that these are textures generally considered pleasant, appetite-stimulating, and indicative of freshness.
Crisp, crunchy foods are usually served at the beginning of meals or between meals because they're considered accents (potato chips, celery, onions, green pepper, raw vegetables). Smooth foods are considered more satisfying. These can be dishes with broth and sauces, mashed potatoes, puddings, frostings, and syrups.
The words crisp and crunchy are more related to the sound a food makes than to any specific physical property. Dr. Schiffman points out that celery, for example, is crisp because its cells have turgor, which, ''during mastication, the teeth burst the individual cells like balloons.''
Potato chips are crisp because they make a shattering sound when chewed, and fragmentation follows.
Often people think the dishes they're being served today don't taste as good as the food of their childhood or the food of ''the old country.'' It could be, however, that the person's taste perception has changed.
Crisp or crunchy foods, plus a wide range of textures, will help compensate for a loss or change in taste and will increase sensory effect.
Sweet, sour, salty, and bitter are the four basic qualities once thought to cover the range of taste sensations resulting from the taste buds.
Some experts would add a fifth taste - metallic. But in the past, all other tastes were assumed to be combinations of the basic four. Research in Dr. Schiffman's laboratory, however, demonstrates that there are many more.
''We simply do not have the words to describe the broad range of taste quality, because our English vocabulary for taste is so limited,'' she says.
''The sense of smell is even more complicated than taste, and we can discriminate thousands of aromas from one another.
''The majority of food aromas stimulate the olfactory receptors while food is being swallowed, and 80 percent of what we often call 'taste' is actually 'aroma.' ''
Dr. Schiffman conducted a blindfold demonstration to show the importance of texture and aroma and the subtle differences in tastes of various people.
She asked four blindfolded food editors to guess a vegetable from a spoonful taste of puree. The pureed vegetable was broccoli. All the food editors were wrong, and each one of us had a different answer. I guessed cucumber.
Dr. Schiffman suggests some ways of getting more flavor from the food you eat.
''It is important to switch around from food to food during a meal to maximize sensory impact and eliminate sensory fatigue.
''If we eat three bites of the same food in a row the first bite tastes strong; the second bite weaker; the third with barely any taste at all. There will be more taste and aroma from a meal if we never eat two of the same foods consecutively.''
Artificial flavor mixtures can be used to enhance or bring out a special flavor. For example, an artificial maple flavor can be used to enhance the aroma of applesauce.
Other flavor intensifiers available commercially include those with the taste of boiled potato, tuna fish, cheese, flour, mushrooms, apple, and tomato.
Here is a recipe for paella that illustrates many aspects of taste, aroma, and texture. It is from a booklet of oven and skillet rice dishes that can be prepared quickly and in one dish.
It is available free by sending name and address to ''Cooking Without Looking ,'' Uncle Ben's Inc., PO Box 11877, Chicago, Ill. 60611.
Dr. Schiffman's analysis of the paella follows the recipe. Pacific Paella 4 chicken breast halves, boned, skinned 1 teaspoon paprika 1 teaspoon salt, optional 1/4 teaspoon black pepper 3/4 pound mild Italian sausage 20 sun-dried tomatoes, packed in oil, chopped, drained (about 1 cup) 2 cans (about 13 ounces each) chicken broth 1/2 teaspoon turmeric 1/4 teaspoon saffron, optional 2 cups rice 1 large onion, cut in wedges 2 cloves garlic, minced 1 pound medium shrimp, cooked 1 green pepper, in thin strips 10 mussels, steamed, optional
Cut chicken breasts in 1-inch strips. Combine paprika, salt and pepper, add chicken and stir until seasoning covers meat. Remove sausage casing and cut in 1 /4-inch pieces. Dry tomatoes with paper towel.
Add enough water to chicken broth to make 3 3/4 cups and bring to boil in 12 -inch skillet. Add turmeric, saffron, rice, onion, garlic, chicken, sausage, and tomatoes.
Cover and simmer 20 minutes, then remove from heat. Stir in shrimp, green pepper, and mussels. Let stand, covered, until all liquid is absorbed, about 5 minutes. Dr. Schiffman's analysis:
This dish is ideal as an example of many desirable textures. Both chicken and Italian sausage are chewy and spongy. Italian sausage and tomatoes are granular. Tomatoes also provide a soft, juicy texture, while chicken broth provides a watery component.
Onion and green pepper are crisp. Minced garlic is grainy. Shrimp is spongy yet hard, and mussels tend to be spongy and slippery. The rice with its separate grains contributes a fluffy, granular component.
The aroma is a synthesis of the aromas of chicken, paprika, pepper, sausage, tomatoes, onion, garlic, shrimp, green pepper, and mussels.