Food preservation
 |
| This article is part of the Food theme. Alimentation |
Food preservation consists in preserving the gustatory and nutritionary properties of food while keeping the products healthy, of course.
Perishable food will spoil owing to the action of various organisms such as insects , rodents, fungi, germs, or substances (eg, oxydation). These degradations modify the texture, the coulour and the taste of the food that may become unhealthy.
Techniques had to be found to be able to store food while it is available and consume it later, according to the season or in case of famines.
Contents |
[edit] Refrigeration
Cooling food and keeping it at low temperatures is the easiest and most common solution but it also involves using the most energy consuming of household appliances (after central heating and air conditioning)...
Cooling food and storing it at low temperatures slows the action of micro-organisms for four to ten days (about 39 to 42°F.
[edit] Deep freezing
The idea is the same, only the temperatures are much lower : between -1 °F and -22 °F. If the cooling down period is short, there'll be few cristals of ice and the tissue will not be modified. The conservation is much longer, up to several months.
Acid foods do not have to be blanched (tomato, bell pepper, small fruits or rhubarb). They simply have to be stored in a freezer bag or a reusable plastic box, stick a label indicating the nature of the food and the date, you can keep it for a full year .
Blanching is advised for other vegetables to stop the decaying process. Blanching is a cooking process : either boil or steam for a few minutes, depending on the kind of vegetable. Dry the food to prevent the formation of ice later, once the food has cooled down, wrap and store.
Tip : keep the list of your provisions uptodate and stick it on your deep freezer!
[edit] Cold rooms
Storing the vegetables in a cellar is a good way of preserving them fresh till the end of winter. The cellar can be an underground basement (possibly cemented) and naturally aerated. If need be, add ventilation grilles : one near the floor to let cold air in and one near the ceiling to let warm air out.
The temperature should ideally be around 32 to 35°F Celsius. Some vegetables (gourds, eg) are to be stored at around 58°F, so preferably in a cool closet within the house.
Here is a list of vegetables to be stored in a cold room : garlic, beetroots, carrots, cabbages, onion, parsnips, and potatoes (mind these are to be stored seperately as they let out. Pour ce qui est de la pomme de terre, il faut l'isoler, car elle dégage de l'ethylene and would spoil other foods near by.
Food must always be refregerated as soon as possible after harvesting to stop the decaying process right from the start.
[edit] Heating
Microbes develop as soon as the temperature nears 50°F, from 145°F upwards, they begin to die out.
- Pasteurization (between 149 and 212°F)
- Sterilization (between 239 and 248°F)
[edit] Preserves and conserves
There are two techniques... Either in boiling water or using pressure. The processa aims at destroying the spores of Clostridium botulinum that would make preservation at ambient temperature hazardous. To preserve food, choose a tested recipe and respect the recommandations as to ingredients, quantities and duration of the treatment.
Acid foods should be boiled (fruits and tomatoes - add lemon juice to tomates to increase their acidity). For less acid foods (vegetables, meat and prey, fish and sea food, soups, stews, prefer pressure to reach a temperature of 240 degrés Fahrenheit : recommended for safe preservation.
[edit] Equipment for home-made conserves
The glass jars must be thick to stand the heat and be air-tight. Jars are made of annealed or tempered glass . Annealed glass won't stand differences of temperature of more than 140°F whereas tempered glass can resist differences of up to 300°F. Heat and cool the jars progressively. Jars come in various shapes and sizes and may have two types of sealing : twisting or screwing lids.
Jars with a metal screwing lid (Mason jar) are less common in Europe than in Northern America. Their advantage is the lid is a part in itself and made of two parts : the lid and a ring band so you can check it's air-tight by pressing with your finger and you only have to change the ring band the next time.
Jars with a glass lid are one only part. The lid is surrounded by an iron handle that is sealed by means of a spring. A rubber disk makes it air-tight (to be changed after each use) .
You may also need a large funnel and a magnet plier to manipulate the jars. To boil the jars, use a high sterilizer with a rack, cover with at least 1 in. of water, 2 in. for vigourous boiling.
A pressure pot or "autoclave" will sometimes have a manometer indicating the pressure inside. Using a pressure cooker is not recommended for the pressure will be too low compared to that needed. Choose a high autoclave that can contain high jars or several rows of piled smaller jars.
Prefer a propane burner : the heat will be more regular than that of a cooker. Boiling will be quicker and the pressure more appropriate.
[edit] Sealing
Sealing is key to success. During the heating, the air is let out of the jar. So do not screw too tightly. During the cooling, the steam that had pushed the air out condenses, the food is conserved in vacuum, it contracts and the lid cambers a little. This is the sign everything is well! Let sit for 24 hours, label the jars, remove the ring bands and store in a dark room.
Making conserves can be very tricky so it's a good idea to start with an experienced person. Also, it's time consuming if you consider all the work from cropping (or even sowing) to canned food.
In exchange you'll top quality products and once your equipment is cost-effective, it will really be profitable. Pressure conserves are less nice because the food cooks for so long but it remains a good way of saving electricity.
[edit] Drying
Drying consists in removing the water from a product. This can be done through heating, creating a vacuum or using chemicals that'll absorb the water (eg concentrated sulfuric acid), or through slow progressive drying.
This is a way of preserving food in so far as microbes can't develop without water.
Dehydration is a particularly well adapted way of preserving herbs, fruits or even vegetables. Dehydration and lactic acid fermentation are the healthiest methods of food preservation as the vitamins are kept intact and rebuild themselves when the food is rehydrated. Besides, this sort of food is easy to carry (eg for holidaymakers) and medicinal herbs, they keep all their properties
There are solar dryers : especially useful for cold or temporate climates (Quebec...), though they can be used in Summer only, when nights get colder, drying is less easy as moist can penetrate the plant if there is no additional heating.
See the article Solar dryer.[edit] Slow drying
Herbs can also be left to dry in the open air, in the dark, upside down, on a sheet or a mosquito net. Only the process is low and the products will be of poorer quality.
[edit] Fermentation
Fermentation is another means of preserving food, especially for alcoholic drinks, sauerkraut, yogourts, cheese, kefir....
The two main types of fermentation used to preserve food are alcoholic fermentation and lactic acid fermentation.
These techniques are 10 000 years old and these traditional methods should be perpetuated because they offer remarkable properties.
[edit] Natural antiseptics
Salt, sugar, acids (vinegar), alcohol... prevent bacteria from developing but don't stop the oxidation of vitamins.
[edit] Alcohol
Alcohol is a perfect antiseptic as it kills germs ; it is used to preserve fruits , however the fruit won't keep all their qualities as their sugar and flavour will dissolve in alcohol. Sugar must be aded to the conserve. The fruits are kept in flavourless spirit in large corked jars or sealed with a glass lid and a rubber band
[edit] Sugar
Food preservation with sugar implies heating. The water contained in the food must evaporate, at least partly. Boiling or sterilization will concentrate the sugar. This process is used for : Par l'ébullition et le sucre, on va obtenir des préparations d'aspects différents.
[edit] Vinegar
Vinegar is an excellent antiseptic because it contains acetic acid that prevents germs from developing. Either let the food sweat or boil to remove the water, then immerge in spirit vinegar, heat the vinegar to keep the natural green colour of vegetables, typically used for pickles.
[edit] Salting and smoking
These methods consist in incorporating salt, and optional additives and mostly used for meat , the process is used in association with fermentation, drying, cooking, smoking, which are complementary treatments for conservation.
[edit] Dry salting
You'll need some 11 lb of salt for 24 lb of meat. Rub the meat on all sides with salt and alcohol, especially around the bones, put one layer of salt and one layer of meat alternately. Let sit for six weeks, the meat will have lost 25 % of its weight. Good germs will develop and let out lactic acid ; as the salt absorbs the water, bacteria can't develop.
[edit] Brining
Brining consists in immerging food in a mixture of water and salt (0.5 lb of salt for 2 pints of water), this process is used for vegetables (beans, tomatoes, olives, pickles). You can add thyme and bay laurel. Plunge in clear water to soak the food, change the water several times and cook without adding salt to the preparation.
[edit] Dry smoking
This method is contraversal as it may cause health problems. It consists in treating the food with the compound gases that are let out when the vegetables burn. The food can then be kept for a long time, this is why it is one of the oldest ways of preserving food ; it also adds a specific flavour and colour to the original product. It can be done with or without heating, a moderate temperature will soften the texture too.
[edit] See also
[edit] Internal links
- Preserving grapes, Preserving apples
- Seasonal fruits and vegetables
- Food
- Food boxes and wrapping
- Doing without a deep freezer
[edit] External links
[edit] Bibliography
- Preserving Food without Freezing or Canning: Traditional Techniques Using Salt, Oil, Sugar, Alcohol, Vinegar, Drying, Cold Storage, and Lactic Fermentation by Gardeners and Farmers of Centre Terre Vivante ; Chelsea Green Publishing,2007, ISBN 1933392592
|
|
Portal Food – Reach the Food-related articles. |
