Processing method:

Heating of food by boiling, baking, frying, roasting/grilling, steaming or smoking.

Description of method:

Food is heated using hot and dry air (e.g. in an oven), hot steam (e.g. in a steam cooker), direct contact with a hot surface (e.g. in a frying or cooking pan) or radiating heat (e.g. over an open fire).

Advantages:

• Converts nutrients into a form that is more easily digestible by the human body (e.g. starchy food such as potatoes or cereal grains, raw meat).
• Produces the desired texture and flavor in food.
• Kills harmful microorganisms that can lead to illness.
• Destroys substances that would otherwise interfere with the digestibility of the proteins or produce toxic effects in the body (e.g. anti-nutrients found in legumes such as soya beans, lima beans, lentils and chickpeas).
• In the case of heating egg whites and some fish, it makes biotin and vitamin B1 better absorbable.
• Heating flour by baking increases the amount of niacin that can be utilized by the body.
• Losses of protein and carbohydrate during cooking are generally small.

Disadvantages:

• Heating can destroy heat-sensitive nutrients, such as vitamin C, and to a lesser extent vitamin B1 and the other water-soluble vitamins.

Common examples:

Baking bread, cooking vegetables in soups, grilling meat, stir-frying vegetables, deep-frying dough.

Tips:

• Shortening the cooking time increases the amount of nutrients retained (" use of pressure cooker).
• Water-soluble vitamins dissolve in the cooking water, so it is advisable to minimize the amount of water used to cook for examples fruits and vegetables and to not throw away the cooking water, but rather, to incorporate it into food.

Processing method:

Food (usually in liquid form) is heated for a short time for the purpose of killing harmful (but not all) micro-organisms and some enzymes.

Description of method:

Two main methods:

(a) batch processes in which a liquid is heated in a container to a specific temperature. Can be done easily without specialized equipment (for example: milk is heated to 63 °C and kept at this temperature for 30 minutes);

(b) continuous process, in which steam is injected into a constant flow of liquid (for example, milk pasteurization equipment heats milk to 73 °C for 15 seconds before the milk is cooled down again. However, industrial equipment is necessary for this processing method.

Advantages:

• Increases safety of milk and fruits/vegetable juices by destroying microorganisms that may cause illness (by pathogens).
• Slows down the spoilage of milk because microorganisms and enzymes are destroyed that contribute to a reduced quality and shelf life.

Disadvantages:

• Pasteurization appeared to qualitatively reduce concentrations of vitamins B12 and E.

Common examples:

Pasteurization of fresh milk, ice cream, fruit juices or beer.

Useful tips:

• It is always a combination of temperature and holding time that will cause the desired pasteurization effect. The higher the temperature, the shorter the holding time needs to be.
• Shorter heating times result in better taste and less loss of vitamins.
• To delay spoilage and nutrition loss during storage, store food in a refrigerator or cool surroundings and away from light after pasteurization.
• At higher altitudes, the boiling point of water, and liquids in general, is lower (100 °C at sea level-0m, 93 °C at 2’000m, 87 °C at 4’000°C). The temperatures necessary for pasteurization, however, are not changed.
• Attention: Adding larger quantities of sugar raises the boiling point (e.g. when making marmalades).

Processing method:

Grinding

Description of method:

Physical grinding process to produce flour or meal.

Advantages:

• Brings agricultural ingredients into a form which can easily be stored, and possibly further processed.
• Makes the ingredients more easily digestible because they are ground into smaller pieces.

Disadvantages:

• Milling and refining processes, in which the coarse fibrous bran or seed coat of the grain is removed, results in significant nutrient losses particularly of fat (found in the germ of cereals), B-vitamins, niacin and minerals (found in the outer layers).

Common examples:

Grains, legumes

Useful tips:

Foods made from whole meal flour are better sources of nutrients than those prepared from white and refined flour.

Processing method:

Reducing water content through air drying (including solar drying)

Description of method:

Moisture is removed by passing hot air past the product. Several methods exist: direct, indirect, mixed mode, natural circulation, forced circulation. Air can be ambient temperature (not specifically heated), or hot (heated, for example, by an oven or solar energy).

Advantages:

• Retains many nutrients while enabling storability of the product under ambient temperatures.
• Inhibits microbial growth: drying lowers the amount of free unbound water available for microbial growth in food. Since microorganisms need certain amounts of free water for growth, their growth is halted below defined minimum levels of moisture (e.g. bacteria, yeasts and molds).
• Causes a reduction in weight and volume, minimizing packing, storage, and transportation costs.

Disadvantages:

• Loss of thiamine and vitamin C.
• Increased risk of damage and post-harvest loss by pests and growth of unwanted microorganisms (e.g. mold) during the drying process.
• Variable quality products due to over- or under-drying.
• Large areas of land or surface space on drying tables/trays may be needed for the shallow layers of food.
• Slow drying in cloudy or humid weather and at night if sunlight and/or dry air are needed. The use of electric dryers produces better quality, but access to electricity is not always given and may be expensive.

Common examples:

Vegetables (tomatoes, onions, etc.), fruits (apples, berries), herbs, meats, etc.

Useful tips:

• Agricultural products, especially fruits and vegetables, require hot air in the temperature range of 45–60 ˚C for safe drying.
• Sun drying is only possible in areas where the weather allows foods to be fully dried immediately after harvest.

Processing method:

Anaerobic process that produces chemical changes in organic substrates through the action of enzymes

Description of method:

With enzymes, carbohydrates are degraded by producing lactic acid, to produce e.g. sour foods as pickled cucumbers, kimchi, and yogurt, as well as alcoholic beverages such as wine and beer. Under controlled conditions (e.g. temperature), the growth of ‘good microorganisms’ is encouraged while the growth of ‘bad micro-organisms’ is inhibited. Quick heating is sometimes used to end the fermentation process by killing the fermenting microorganisms (e.g. production of alcoholic beverages).

Advantages:

• Can be applied to many different types of foods.
• Usually does not require any specialized equipment.
• Synthesis and availability of nutrients: Fermentation can increase the availability of vitamins and minerals for human bodies to absorb. Additionally, by boosting the beneficial gut bacteria (intestines), the bacterial flora is better able to manufacture B vitamins and synthesize vitamin K.
• Digestions and absorption: As some of the sugars and starches in food are broken down through the process, fermented foods are easier to digest. For example, fermentation breaks down the lactose in milk to simpler sugars (glucose and galactose) which can make products such as yogurt and cheese potentially easier to digest, which is relevant especially for people with lactose intolerance.
• Immune functions: Fermented foods are rich in probiotic bacteria. So by consuming fermented foods, beneficial bacteria and enzymes are added to the intestinal flora, increasing the health of the gut (digestive system), which helps to enhance the immune system.

Nutritional disadvantages:

• Some people dislike the sour taste of fermented foods.

Common examples:

Dairy products (kefir, yoghurt, cheese); vegetables and tubers (sauerkraut and kimchi [fermented cabbage]); foufou [fermented cassava], pickles; legumes and grains (sourdough bread; miso; tempeh; injera [bread from fermented teff]); beverages (wine, beer and other alcoholic beverages; kombucha).

Useful tips:

• Use starter cultures or small amounts of a previously fermented product to start or speed up the fermentation process.

Processing method:

Application of liquids and smoke to conserve food, especially meat

Description of method:

Curing: Use of salt, acid and/or nitrates. When salt is used, the method is called ‘Salting’. During salting, the salt draws out moisture and creates an environment in which bacteria cannot grow.

Smoking: Use of hot or cold smoke to dry the product and to incorporate smoke particles into the food. Cold smoking changes the color and flavor of the food, but the food is not cooked or preserved by the process. Hot smoking cooks and dries the product as well as changes the color and flavor.

Advantages:

• Can greatly increase shelf life, up to many years.
• These are ancient preservation techniques, which do not require specialized equipment.

Disadvantages:

• Eating smoked products may increase the risk of cancer development in some parts of the world – especially if technology is not well applied.

Common examples:

Cured sausage

Useful tips:

Smoked meat is less likely to turn rancid or grow mold than unsmoked meat.

Processing method:

Use of meaningful amounts of salt to preserve foods by either anaerobic fermentation in brine or immersion in vinegar.

Description of method:

Pickling is widely used to preserve meats, fruits and vegetables. The use of salt combined with vinegar effectively inhibits bacteria growth, with a pH of 4.6 or lower.

Advantages:

• Very simple technology, not requiring big investments.
• The high sugar content and acidity of all preserves prevents mold growth after opening the pack, so that it can be used a little at a time.

Nutritional disadvantages:

• Increases salt content of food.
• Increases the sugar content of the food (more ‘empty calories’, increased risk of cavities.

Common examples:

Chutney, escabeche

Useful tips:

Try to conserve meat, fruits, vegetables, cheese. To make pickles, cucumbers are soaked in a 10-percent salt-water brine for several days, then rinsed and stored in vinegar to preserve them for years.