Convection in Food Science

Effects of Heat on Foods

• Fast-moving molecules in hot substances transfer energy to slower molecules in cold substances, causing them to heat up.
• Foods are composed of proteins, fats, carbohydrates, water, minerals, vitamins, and pigments.
• Carbohydrates in foods include starches, sugars, and fiber, with caramelization and gelatinization being important heat-induced changes.
• Proteins in foods coagulate and undergo Maillard reaction when heated, affecting the texture and flavor of meats, poultry, fish, eggs, and milk products.
• Fats present in foods can be solid or liquid at room temperature and have specific smoke points when heated.
• Connective tissues in meats can be dissolved when cooked slowly with moisture or with the help of acids like lemon juice or vinegar.
• Minerals, vitamins, pigments, and flavor components in foods are essential for nutritional quality, appearance, and taste.
• Water is present in nearly all foods and exists in three states: solid, liquid, and gas. Emulsions, such as mayonnaise and vinaigrette, are a mixture of two normally unmixable substances.
• Heat must be transferred to all parts of the food for it to be cooked, which occurs through conduction, convection, and radiation.
• Conduction and convection play key roles in heat transfer, with conduction occurring through direct contact and convection through the movement of air, steam, or liquid.
• Radiation is another form of heat transfer, where heat is emitted in the form of waves or particles.
• Understanding the effects of heat on different food components is crucial for selecting cooking methods that preserve nutrients, taste, and appearance.

Cooking Methods and Heat Transfer in Food Science

• Convection is the process that transfers heat from the heat source to the food, occurring when heat moves directly from one item to something touching it or from one part of something to an adjacent part.
• There are two kinds of convection: natural, where hot liquids and gases rise while cooler ones sink, and mechanical, where fans speed the circulation of heat in convection ovens and steamers.
• Heat transfer in cooking also involves radiation, which occurs when energy is transferred by waves from a source to the food, such as in broiling and microwave radiation.
• Cooking methods are classified as moist heat or dry heat, with moist-heat methods involving the conduction of heat to the food product by water or water-based liquids, and dry-heat methods involving hot air, hot metal, radiation, or hot fat.
• Dry-heat methods include baking, roasting, barbecue, pan smoking, broiling, grilling, griddling, pan-broiling, sautéing, pan-frying, and deep-frying.
• Moist-heat methods include boiling, simmering, poaching, blanching, steaming, cooking en papillote, braising, and stewing, each with specific temperature and cooking techniques.
• Water boils at 212ºF (100ºC) at sea level, and simmering occurs at a temperature of about 185ºF to 205ºF (85º to 96ºC).
• Cooking sous vide involves vacuum-sealing food and cooking it in a water bath with precise temperature control.
• Infrared cooking occurs when the radiation generated by the oven penetrates partway into the food and agitates the molecules of water, creating heat that cooks the food.
• The time it takes to achieve doneness is affected by cooking temperature, speed of heat transfer, and the size, temperature, and individual characteristics of the food.
• The term baking usually applies to breads, pastries, vegetables, and fish, while roasting usually applies to meats and poultry.
• Braised meats are usually browned first using a dry-heat method, then finished with a moist-heat method, and consist of large pieces of food, at least portion-size, cooked by the braising method.