From TheBestLinks.com
In its strictest sense fermentation is the energy-yielding anaerobic metabolic breakdown of a nutrient molecule, such as glucose, without net oxidation. Fermentation yields lactate, acetic acid, ethanol, or some other simple product.
Fermentation is also used much more broadly to refer to the bulk growth of microorganisms on some medium. No distinction is made between aerobic and anaerobic metabolism when the word is used in this sense.
This process is often used to produce or preserve food. Fermentation typically refers to the fermentation of sugar to alcohol using yeast, but other fermentation processes include the making of yogurt. The science of fermentation is known as zymology.
Fermentation usually implies that the action of the microoganisms is desirable.
Uses
The primary benefit of fermentation is the conversion, e.g. converting juice into wine, grains into beer, and carbohydrates into carbon dioxide to leaven bread.
According to Steinkraus (1995), traditionally food fermentation serves five main purposes:
- "Enrichment of the diet through development of a diversity of flavors, aromas, and textures in food substrates"
- "Preservation of substantial amounts of food through lactic acid, alcoholic, acetic acid, and alkaline fermentations"
- "Enrichment of food substrates biologically with protein, essential amino acids, essential fatty acids, and vitamins"
- "Detoxification during food fermentation processing"
- "A decrease in cooking times and fuel requirements"
Fermentation has some benefits exclusive to foods. Fermentation can produce important nutrients or eliminate antinutrients. Food can be preserved by fermentation, since fermentation uses up food energy and can make conditions unsuitable for undesirable microorganisms. For example, in pickling the acid produced by the dominant bacteria inhibit the growth of all other microorganisms.
Fermentated foods, by region
- Worldwide: olives, vinegar, wine
- India: achar, gundruk, Indian pickles
- South East Asia: asinan, bai-ming, belacan, burong mangga, dalok, jeruk, fish sauce, kimchi, leppet-so, miang, nata de coco, nata de pina, naw-mai-dong, pak-siam-dong, paw-tsay, phak-dong, phonlami-dong, fish paste, sajur asin, sambal tempo-jak, santol, si-sek-chai, sunki, tang-chai, tempeh, tempoyak, vanilla
- East Asia: cha-ts’ai, dan moogi, dongchimi, hiroshimana, hot pepper sauce, jangagee, kachdoo kigactuki, kakduggi, kimchi, miso, mootsanji, nara senkei, natto, narazuke, nozawana, nukamiso-zuke, oigee, oiji, oiso baegi, omizuke, pow tsai, red in snow, sake, seokbakji, siozuke, soy sauce, szechwan cabbage, tai-tan tsoi, takana, takuan, totkal kimchi, tsa tzai, tsu, umeboshi, wasabi-zuke, yen tsai
- Africa: hibiscus seed, hot pepper sauce, lamoun makbouss, mauoloh, msir, mslalla, oilseed, ogili, ogiri
- Americas: pickles, sauerkraut, lupin seed, oilseed, vanilla
- Middle East: kushuk, lamoun makbouss, mekhalel, torshi, tursu
History
Since fruits ferment naturally, fermentation preceeds human history. However, humans began to take control the fermentation process at some point. There is strong evidence that people were fermenting beverages in Babylon circa 5000 BCE, ancient Egypt circa 3000 BCE, pre-Hispanic Mexico circa 2000 BCE, and Sudan circa 1500 BCE. There is also evidence of leavened bread in ancient Egypt circa 1500 BCE and of milk fermentation in Babylon circa 3000 BCE. The Chinese were probably the first to develop vegetable fermentation.
Types of Fermentation
there is also milk fermentation
Yeast Fermentations
- See: Yeast
Bacterial Fermentation
- See: Bacteria
Mixed and Multiple Fermentations
Many products require multiple fermenting agents to produce the final product. The most common example is vinegar; yeast converts sugars to alcohol, then aerobic bacterium convert the alcohol to acetic acid.
There are also undesirable multiple fermentations. Wine can sometimes become 'ropey' from lactic acid bacteria.
Biology of Fermentation
Agents
- See: Yeast, Fungus, Bacteria
Energy Sources
- See: Carbohydrates
Sugars
"Ordinary cane sugar, uncrystallizable fruit sugar, grape sugar and glucose, are the three most important varieties. Fruit sugar exists in all of the sub-acid fruits such as grapes, currants, apples, peaches, etc. When these fruits are dried, the fruit sugar changes to grape sugar forming the whitish grains which are seen on the outside of prunes, raisins, etc. Grape sugar is found to a limited extent in fruits associated with fruit sugar. Cane sugar is readily changed by the action of acids or ferments into fruit sugar, and the latter into grape sugar, but the process cannot be reversed. Grape sugar is the only fermentable variety, the others becoming changed into it before fermentation."
Complex Carbohydrates
"Under the influence of acids, or diastare, a principle existing in germinating grains, starch is changed first into gum (dextrine) and afterwards into grape sugar. Hence one of our most important sources of alcohol is to be found in the starch of barley, corn, wheat, potatoes, etc. Wood may be converted into grape sugar by the action of strong sulphuric acid which is afterwards neutralized. An attempt to produce alcohol in this way on a commercial scale was made in France, but was not successful."
Environment
Control of the fermentation process is achieved by controlling the condtions in which the medium is stored. All organisms have a particular range of conditions in which they are able to thrive; outside this range their action is surpressed. The best example of this are honey and molasses, which is full of simple sugars, yet are stable for decades: the low water availability retards any microbial growth. In general, conditions are controlled so that only the desired fermentation is able to take place.
Microbes: environments for optimal growth
|
| Typically Desirable
| Typically Undesirable
|
|
| Yeast
| Lactobacter
| Acetobacter
| Fungi
| Putrefactive Bacteria
| Pathogenic Bacteria
|
| Temperature, °C
| 10–35
| 37–50
| 25–35
| 10–35
| 21–38
| 20–45
|
| Oxygen
| Any
| Anaerobic
| Aerobic
| Any
| Anaerobic
| Usually Aerobic
|
| Acidity (pH)
| 3.7–4.6
| 3.1–4.5
| 3–8
| 2–8.5
| 6–8.2
| 4.6–9.3
|
| Available Water
| >0.8
| >0.9
| >0.9
| >0.7
| >0.9
| >0.9
|
| Alcohol by Volume
| <15%
| <13%
| <7%
| <15%
| intolerant
| intolerant
|
Selected fermentation media
|
| Honey
| Milk
| Fresh apple
| Apple juice
| Fruit wine
| Dried apricot
| Cucumber
| Cucumber Pickles
|
| Acidity (pH)
| 3.7–4.2
| 6.4–6.8
| 3.3–3.9
| 3.4–4.0
| 3.3–3.5
| 3.3–3.5
| 5.1–5.8
| 2.2–4.6
|
| Available Water
| 0.5–0.7
| 0.97
| 0.97
| 0.97
| 0.97
| 0.50–0.75
| 0.97
| 0.93
|
| Alcohol by Volume
| 0%
| 0%
| 0%
| 0%
| 5%
| 0%
| 0%
| 0%
|
Temperature
Temperature affects all microbes and enzymes greatly. High temperatures destroy microbes, and low temperatures suspend them, although the temperatures that these happen at depend on the particular microbe.
Oxygen
Microorganisms have differing relationships to air; some require it, others require its absence. In the production of alcohol, often a fermentation lock is used to prevent oxygen from entering the ferment, since this prevents the growth of aerobic bacteria. Conversely, in the production of vinegar oxygen is bubbled through the ferment to encourage aerobic acid-producing bacteria.
Acidity
In general, yeasts prefer acidic conditions, while bacterium prefer neutral conditions. Fruits are naturally acidic, so the action of yeasts and fungi is encouraged.
Available water
There are two types of water in a medium: bound and available. Bound water, for example ice, is not available to microbes. The presence of some available water is necessary for fermentation to occur.
Water availability is measured by water activity. Pure water is defined to have a water activity of 1. Fungi usually require at least 0.7, yeast at least 0.8, and bacteria 0.9. Dried foods, molasses and honey cannot support fermentation since their water activity is 0.65 or lower. When honey is used in ferments, it must be mixed with water first.
Alcohol
Yeast cannot survive in high alcohol concentrations. This is why distillation is necessary — no natural fermentation can produce greater than 20% alcohol by volume. Only a few types of yeast can survive up to even 20%, many can only tolerate 5%–10%.
Other Chemicals
There are specific chemicals that have a great effect on fermentation.
Nitrogen is necessary for the growth of microorganisms; it is frequently added to ferments that lack it, such as those made from honey. Without added nitrogen, it can take years to produce mead from a honey ferment.
Sulphites are commonly used in wine production. When grapes are first harvested, they are covered with natural yeasts. If the winemaker wants a more controlled fermentation, they will kill these yeasts with sulphites and use their own yeast culture. Also, sulphites are used to prevent a fermentation from continuing. For example, the winemaker may want to make a sweeter wine, or to prevent fermentation after bottling. Uncontrolled fermentation after bottling is undesirable since it can cause explosions as carbon dioxide builds up.
Products
Yeast produce ethanol and carbon dioxide gas. When the ferment has a high concentration of pectin minute quantities of methanol can be produced. Usually only one of the products is desired; in bread the alcohol is baked out, and in alcohol production the carbon dioxide is released into the atmosphere.
Bacteria generally produce acids. Vinegar (acetic acid) is the direct result of bacterial fermentation. In milk, the acid coagulates the casein, producing curds. In pickling, the acid preserves the food from pathogenic and putrefactive bacteria.
References
- Steinkraus, K. H., Ed. (1995). Handbook of Indigenous Fermented Foods. New York, Marcel Dekker, Inc.
- The 1811 Household Cyclopedia
External Links
es:Fermentación
da:Fermentering
de:Fermentation
it:Fermentazione
ja:醗酵
nl:Alcoholische gisting
pl:Fermentacja
Related links
Top visited
0 of
0 links
[no links posted yet]
>> place link >>
Discussion
Last posted
0 of
0 messages
[no messages posted yet]
>> post message >>
Watch
You can
add this article to your own "watchlist" and receive e-mail notification about all changes in this page.
