Vegetable Handling & Storage
Vegetables provide color, flavor and texture to culinary preparations. They are nutrient rich and important in the human diet for maintaining health and preventing diseases. Although humans are omnivores, they originally started out as plant eaters and graduated to eating meats. Today many people choose a vegetarian diet as a matter of health or for ethical reasons.
Fresh vegetables are high in moisture; generally greater than 70% for potatoes and as high as 95% for lettuces. They are low in proteins and fats with a few exceptions such as avocado which has a high fat content and corn which has a moderate fat content.
Vegetables contain digestible carbohydrates in the form of sugars and starches and indigestible ones in the form of cellulose fibers which are important for plant structure plus they provide roughage in the human diet. Another fiber, lignin, is the woody part found at the base of stems including asparagus, broccoli and other vegetables. It is inedible and usually removed from the plant before cooking.
Vegetables are a good source of minerals including calcium, iron, magnesium, phosphorus, manganese, potassium, copper and fluoride, and vitamins especially vitamins A and C particularly in the yellow-orange and green leafy vegetables.
Chlorophyll is a fat-soluble pigment found in green vegetable including broccoli, spinach, and green beans. It is an unstable pigment that is easily affected by heat and acids such as lemon juice or vinegar turning it a drab green. Alkaline found in small amounts of tap water or in the form of baking soda helps preserve color but destroys vitamins and breaks down the structure of the vegetable making it mushy.
Because chlorophyll is such an unstable pigment special care should be taken in the cooking process. In raw vegetables gasses trapped between the cells clouds the bright green color of the vegetables. Cooking releases these gasses and brightens the color. However continued cooking causes a magnesium atom in chlorophyll to detach and be replaced by hydrogen changing the bright green to a dull gray-green color.
Cooking green vegetables in a large quantity of boiling water as quickly as possible and then stopping the process by plunging them into ice water is the best way to preserve the bright green color. This method is known by the French term a l’anglaise.
Carotenoids are fat-soluble pigments found in orange colored vegetables including carrots, sweet potatoes and winter squash varieties. Carotenoid pigments also include lycopene, found in tomatoes, watermelon, and pink grapefruit and xanthophyll giving corn its yellow color. Carotenoids are fairly stable pigments but are affected by heat, acids and alkaline. Overcooking will diminish their bright color. Acids will dull their color and prevent tenderization. Alkaline will brighten their color but soften their texture.
Anthocyanin is a water-soluble red to blue colored pigment found in red cabbage, radishes, and purple or blue potatoes, and fruits including cherries, berries, and apples. When cooking this class of foods, they need help to maintain a stable appetizing color. Plain water turns an anthocyanin plant from its normal hue to a dull and unappetizing blue. Acids including lemon juice, vinegar, tart apple, and wine, will intensify the red color. Because acids will firm the vegetable it is often not added right away in the cooking process. Alkalis will turn anthocyanin an unappetizing green or blue-green and is not recommended during cooking.
Anthoxanthin is a water-soluble white to yellow pigment found in onions, white potatoes, salsify, cabbage, cauliflower, turnips, parsnips, white wheat flour, and pears. It is a relatively stable pigment but overcooking can cause the pigments to discolor and turn a dull yellow to gray or even pink. Acids including citrus juice and vinegar will help to maintain a white color during the cooking process but as with other vegetables should not be added until later in the cooking process because they can prevent the vegetables from softening. Alkalis in the form of baking soda will turn the pigments yellow and the texture mushy.
Betalain is a water-soluble red-yellow pigment found in beets, chard, amaranth, and cactuses. The pigment bleeds easily and vegetables will lose color when cut and cooked in water. Acids will brighten the vegetable and help retain color but will prevent the vegetable from softening so it is best to add after the vegetables begin to tenderize. Beets turn slightly blue in alkaline solutions so baking soda should never be used when cooking them.
Vegetables are often grouped according to their related family such as the cabbage family, the onion family or the mushroom family. Vegetables can also be understood by where their edible portion is located on the plant such as fruits, flowers, or stems. For cooking purposes the easiest way to classify vegetables is their like characteristics. For example starchy root vegetables can be brought together in a class that helps a cook understand how to handle and cook them for optimal results. Salad greens are handled and processed in similar ways regardless of the type or variety of lettuce. Once common vegetable characteristics are understood, a chef can swap and exchange similar vegetables in recipes thus allowing for limitless creative variations.
Vegetable Taste and Texture
Vegetables when freshly harvested have a vibrant sweet flavor with moist and unique textures, however once harvested they quickly begin to lose flavor and their texture changes as well. Vegetables convert their sugar to starches or fibers that are tough in texture and bland in taste. Depending on the vegetable, this can happen quickly, sometimes in a matter of hours. The effects are compounded by the gradual moisture loss that occurs as the vegetables are stored. Yeasts, molds, and bacteria also contribute to the deterioration of vegetables. Conversely, many vegetable varieties are quite hardy and can often be stored for weeks or months before use. Onions, potatoes and other root vegetables hold well.
When it comes to fresh vegetables the best advice is to order products as needed and avoid prolonged storage. Buying local foods will also provide vegetables that are fresher with a longer shelf life because commercially grown produce can take a week or more to reach the market. Avoid purchasing pre-cut vegetables because the loss in flavor, texture, and nutrients occurs all the quicker. Prep what you need on a daily basis and avoid over processing of the vegetables.
Vegetables and fruits often develop brown, gray or red discoloration when bruised or cut. This is caused by a chemical reaction from plants enzymes mixing with phenolic compounds and then being exposed to oxygen. This browning effect can be minimized by coating the vegetables or fruits with citric acids including lemon juice or vinegar. Potatoes can be peeled and placed in water to prevent browning. Chilling the vegetables below 40˚F/4˚C will slow the process. Blanching or cooking in water will destroy the enzymes. Immerse fresh cut salad greens in warm water (115˚F/47˚C) for a few minutes before chilling.
Although modern farming and transportation allows a chef to purchase almost any type of produce year round it makes sense to buy in season whenever possible. Seasonal produce will usually have superior flavor and texture, is more cost effective, and can often be purchased locally.
Purchasing and Storing Vegetables
Most produce is stored under refrigeration 40-45˚F/4-7˚C with a relative humidity rate of 80-90%. Exceptions to this rule include potatoes and onions which should be stored at 45-55˚F/7-12˚C and winter squash varieties that should be stored at 50-55˚F/10-12˚C. Moisture promotes deterioration of produce so it is best to avoid cleaning or trimming vegetables until they are needed. Some vegetables including mushrooms, onions, and potatoes need air circulation to avoid molding and should not be sealed in plastic or air-tight containers. Tomatoes should never be refrigerated because the cold changes the texture to soft and mealy. Purchase produce with the goal of using it within 3 days.
Produce deteriorates quickly in flavor and texture when processed. Leave vegetables whole and intact until ready to use. Avoid trimming or washing prior to storage. Once processed use as quickly as possible to maximize the flavor, texture, color, and nutrients.
Washing & Soaking
- Clean vegetables to remove dirt or other impurities.
- Leafy greens are often soaked to remove dirt and other impurities and as a way to refresh them.
Trimming & Cutting
- Trim vegetables minimally to maximize yield.
- Use vegetable trim for stocks or soups
- Compost inedible trim
- Soak potatoes in water after peeling
- Some produce requires soaking in acidic liquid (citrus or vinegar) to prevent browning (artichokes, eggplant, apples)
- Cut and use as close to service as possible