What Is Fermentation?

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.

French chemist Louis Pasteur was the first zymologist, when in 1857 he connected yeast to fermentation. Pasteur originally defined fermentation as respiration without air.

Pasteur performed careful research and concluded, "...I am of the opinion that alcoholic fermentation never occurs without simultaneous organization, development and multiplication of cells... ...if asked, in what consists the chemical act whereby the sugar is decomposed... ...I am completely ignorant of it...."

The German Eduard Buchner, winner of the 1907 Nobel Prize in chemistry, later determined that fermentation was actually caused by a yeast secretion that he termed zymase.

The research efforts undertaken by the Danish Carlsberg scientists greatly accelerated the gain of knowledge about yeast and brewing. The Carlsberg scientists are generally acknowledged with kick-starting the entire field of molecular biology.

With few exceptions, all dietary carbohydrates and proteins can serve as substrates for microbial fermentation. Nonetheless, the crucial advantage of being a herbivore is the ability to efficiently extract energy from cellulose and other components of plant cell walls.

Cellulose fibers account for 40-50% of the total dry weight of stems, leaves and roots. These fibers are embedded in a matrix of hemicelluloses and phenolic polymers (lignin-carbohydrate complexes) that are covalently crosslinked. Cellulose itself is a linear polymer of glucose molecules linked to one another by beta[1-4] glycosidic bonds and herein lies the problem for the vertebrate digestive system. As far as is known, no enzyme able to hydrolyze beta[1-4] glycosidic bonds has evolved in vertebrates. However, a variety of such beta-glucanases are synthesized by microbes. Thus, the diverse population of bacteria and protozoa in the rumen or hindgut produce all the enzymes necessary to digest cellulose and hemicellulose. The glucose released in this process is then taken up and metabolized by the microbes, and the waste products of microbial metabolism are passed on to the host animal. Sugars derived from digestion of soluble carbohydrates such as starch are processed similarly.

Fermentation occurs under anaerobic conditions. As a consequence, sugars are metabolized predominantly to volatile fatty acids (VFAs). Additional major products include lactic acid, carbon dioxide and methane.

The principle VFAs are acetic, proprionic and butyric acids, which collectively provide for the majority of a herbivore's energy needs. The ratio of these VFA's vary with diet, although the majority product is always acetate. On a diet high in fiber, the molar ratio of acetic to proprionic to butyric acids is roughly 70:20:10.

As described above, proteins are also important substrates for fermentation. In caudal fermenters, much of the dietary protein is digested and absorbed prior to the large gut, but in ruminants, all dietary protein enters the rumen. The bulk of this protein is digested by microbial proteases and peptidases. The resulting peptides and amino acids are taken up by microbes and used in several ways, including microbial protein synthesis. However, a large quantity of amino acids ingested by fermentative microbes are deaminated and enter some of the same pathways used for carbohydrate metabolism. The net result is that much of dietary protein is metabolized to VFAs.

Clearly, from the standpoint of the host animal, VFAs are the important product of fermentation. These small lipids are used for many purposes, but the paramount importance of VFAs to herbivores is that they are absorbed and serve as the animal's major fuel for energy production, serving much the same function that glucose does in you. Additional information on the way in which VFAs are put to use is presented in subsequent sections.

Glycolysis (via the traditional Embden-Meyerhoff pathway) is the enzymatic breakdown of glucose into pyruvate. This process requires ADP and NAD+ as co-factors , and produces ATP and NADH inside the cell. A cell can always find a way to hydrolyze ATP back into ADP when needed (no oxidation/reduction is involved in ATP hydrolysis), but NAD+ is a more difficult problem, as its formation involves oxidation of NADH. Under aerobic conditions, the electrons from NADH can ultimately be passed to oxygen, but under anaerobic conditions, another electron acceptor is needed.

During the primary fermentation (H), the fermentable sugars, mainly maltose and glucose are converted to ethanol and carbon dioxide. This action is performed by the brewing yeast, which during the brewing process also produces many of the characteristic aroma compounds found in beer. At the end of the primary fermentation, the yeast cells flocculate and sediment at the bottom of the fermenter and can be cropped and used for a new fermentation. Not all yeast cells sediment; some will remain in suspension, and these cells are responsible for maturation of the beer. During this process the off-flavour, diacetyl is degraded to below the taste threshold. The fermentation characteristics of brewer's yeast are strain-dependent and are genetically inherited. Much of the genetics of Saccharomyces yeasts has been elucidated, and the knowledge gained, forms the basis for breeding of brewing yeast. Thus, new types of beer with altered aromas can be produced with yeast strains selected through breeding.

Malolactic fermentation (MLF, or malo) is an important winemaking process conducted on most red grape wines and some white grape wines. It is also used with some fruit wines. The following article gives information concerning the conditions necessary for MLF, its affects, prevention, progress, suitable wine type candidates for it and yeast compatibility.

Malolactic fermentation bacteria MLF is conducted by lactic acid bacteria (LAB), of the genera Lactobacillus, Pediococcus, and Leuconostoc. Not all LAB are desirable for MLF. Leuconostoc oenos is the most beneficial, and probably the most frequently occurring species of LAB in wine. Species associated with wine spoilage are generally members of Lactobacillus and Pediococcus genera. The Lactobacillus genus, for example, can cause acescence (excessive acetic acid) by metabolising sugar or tartaric acid [Radler and Yannissis, 1972]. Many LAB metabolise pentoses, tartaric acid and glycerol. The term "malolactic fermentation bacteria" (MLB) is commonly used to refer to those LAB strains which are more desirable for MLF. They are more resistant to low pHs such as those in wine (and in which other LAB find it more difficult to live) and they prefer to metabolise malic acid over sugars and citric acid (and they do not metabolise tartaric acid or glycerol).

In brewing, fermentation is the conversion of sugar into carbon dioxide gas (CO2) and ethyl alcohol. This process is carried out by enzymes within a yeast cell. It is in fact a complex series of conversions that bring about the conversion of sugar to CO2 and alcohol. Yeast is a member of the plant family and in brewing we use the sugar fungi form of yeast. These cell gain energy from the break down of the sugar. The by-product, CO2, bubbles through the liquid and dissipates into the air. The alcohol remains in the liquid which is great for us but not for the yeast, as the yeast dies when the alcohol exceeds its tolerance level. Brewer's yeast tolerate up to about 5% alcohol. Beyond this alcohol level the yeast cannot continue fermentation. Wine yeast on the other hand tolerates up to about 12% alcohol. The level of alcohol tolerance by yeast varies from 5% to about 21% depending on yeast strain. The fermentation process has other limits such as temperature. Greater than 27C kills the yeast less and than 15C results in yeast activity which is too slow. The amount of sugar in the solution can be too much and this can prevent fermentation. Some recipes suggest adding the sugar in parts throughout fermentation rather that all at the beginning. This is especially true if the brew is aimed at producing a high level of alcohol. Some yeast strains have evolved to handle higher sugar levels. Yeast such as Tokay and Sauterne.

Fermentation - process by which the living cell is able to obtain energy through the breakdown of glucose and other simple sugar molecules without requiring oxygen. Fermentation is achieved by somewhat different chemical sequences in different species of organisms. Two closely related paths of fermentation predominate for glucose. When muscle tissue receives sufficient oxygen supply, it fully metabolizes its fuel glucose to water and carbon dioxide. However, at times of strenuous activity, muscle tissue uses oxygen faster than the blood can supply it. During this anaerobic condition, the six-carbon glucose molecule is only partly broken down to two molecules of the three-carbon sugar called lactic acid. This process, called lactic acid fermentation, also occurs in many microorganisms and in the cells of most higher animals. In alcoholic fermentation, such as occurs in brewer’s yeast and some bacteria, the production of lactic acid is bypassed, and the glucose molecule is degraded to two molecules of the two-carbon alcohol, ethanol, and to two molecules of carbon dioxide. Many of the enzymes of lactic acid and alcoholic fermentation are identical to the enzymes that bring about the metabolic conversion known as glycolysis. Alcoholic fermentation is a process that was known to antiquity. Before 2000 B.C. the Egyptians apparently knew that crushed fruits stored in a warm place would produce a substance with a pleasant intoxicating power. By 1500 B.C. the production of beer from germinating cereals (malt) and the preparation of wines from crushed grapes were established arts in most of the Middle East. Aristotle believed that grape juice was an infantile form of wine and that fermentation was, therefore, the maturation of the grape extract. Interest in the process of fermentation has continued through the ages, and much of modern biochemistry, especially enzyme studies, has emerged directly from early studies on the fermentation process. One of the earliest laboratories established for the study of biological chemistry was that founded in Copenhagen in 1875 and financed by the brewing family of Jacob Christian Jacobsen.

Fermentation is of different types and takes place under anaerobic conditions mostly in saprophytic microorganisms like certain bacteria and fungi. However, it may also take place in higher organisms under certain conditions.

The two most common types of fermentation are (1) alcoholic fermentation and (2) lactic acid fermentation.

(1) Alcoholic fermentation : the type of fermentation in which ethyl alcohol is the main end product .This is very common in yeast (unicellular fungus) and also seen in some bacteria. Yeast cells release enzymes called zymase complex which bring about the fermentation. The reactions are similar to anaerobic respiration.

(2) Lactic acid fermentation : The type of fermentation in which lactic acid is the end product.

It is carried out by some bacteria (e.g. lactic acid bacteria), and also by animals (muscle glycolysis in animals, under oxygen deficiency, results in the formation of lactic acid this is whay we experience in muscle cramps, or "Charley horse").

Lactic acid bacteria can ferment milk sugar lactose (C12H22O11) to lactic acid. The process is extracellular.

This brings about curdling of milk.

Commercial application of fermentation : There are various kinds of fermentation carried on by different microorganisms. Many of these result in highly useful end products. Such useful microbial activity is used on large industrial scale to obtain the useful end products for the benefit of mankind. Some of the industrial products of the microbial fermentation activities are (a) antibiotics (b) vitamins (c) industrial alcohol (d) bakery products (e) some dairy products (f) tanning of leather (g) curing of tea and coffee (g) lactic acid (h) butric acid, (i) acetic acid etc.

The ancient Greeks understood that important chemical changes took place during this type of fermentation. Their name for this change was "alchemy." Like the fermentation of dairy products, preservation of vegetables and fruits by the process of lacto-fermentation has numerous advantages beyond those of simple preservation. The proliferation of lactobacilli in fermented vegetables enhances their digestibility and increases vitamin levels. These beneficial organisms produce numerous helpful enzymes as well as antibiotic and anticarcinogenic substances. Their main by-product, lactic acid, not only keeps vegetables and fruits in a state of perfect preservation but also promotes the growth of healthy flora throughout the intestine. Other alchemical by-products include hydrogen peroxide and small amounts of benzoic acid.

A partial list of lacto-fermented vegetables from around the world is sufficient to prove the universality of this practice. In Europe the principle lacto-fermented food is sauerkraut. Described in Roman texts, it was prized for both for its delicious taste as well as its medicinal properties. Cucumbers, beets and turnips are also traditional foods for lacto-fermentation. Less well known are ancient recipes for pickled herbs, sorrel leaves and grape leaves. In Russia and Poland one finds pickled green tomatoes, peppers and lettuces. Lacto-fermented foods form part of Asian cuisines as well. The peoples of Japan, China and Korea make pickled preparations of cabbage, turnip, eggplant, cucumber, onion, squash and carrot. Korean kimchi, for example, is a lacto-fermented condiment of cabbage with other vegetables and seasonings that is eaten on a daily basis and no Japanese meal is complete without a portion of pickled vegetable. American tradition includes many types of relishes—corn relish, cucumber relish, watermelon rind—all of which were no doubt originally lacto-fermented products. The pickling of fruit is less well known but, nevertheless, found in many traditional cultures. The Japanese prize pickled umeboshi plums, and the peoples of India traditionally fermented fruit with spices to make chutneys.

Lacto-fermented condiments are easy to make. Fruits and vegetables are first washed and cut up, mixed with salt and herbs or spices and then pounded briefly to release juices. They are then pressed into an air tight container. Salt inhibits putrefying bacteria for several days until enough lactic acid is produced to preserve the vegetables for many months. The amount of salt can be reduced or even eliminated if whey is added to the pickling solution. Rich in lactic acid and lactic-acid-producing bacteria, whey acts as an inoculant, reducing the time needed for sufficient lactic acid to be produced to ensure preservation. Use of whey will result in consistently successful pickling; it is essential for pickling fruits. During the first few days of fermentation, the vegetables are kept at room temperature; afterwards, they must be placed in a cool, dark place for long-term preservation.

It is important to use the best quality organic vegetables, sea salt and filtered or pure water for lacto-fermentation. Lactobacilli need plenty of nutrients to do their work; and, if the vegetables are deficient, the process of fermentation will not proceed. Likewise if your salt or water contains impurities, the quality of the final product will be jeopardized.

Lacto-fermentation is an artisanal craft that does not lend itself to industrialization. Results are not always predictable. For this reason, when the pickling process became industrialized, many changes were made that rendered the final product more uniform and more saleable but not necessarily more nutritious. Chief among these was the use of vinegar for the brine, resulting in a product that is more acidic and not necessarily beneficial when eaten in large quantities; and of subjecting the final product to pasteurization, thereby effectively killing all the lactic-acid-producing bacteria and robbing consumers of their beneficial effect on the digestion.

The recipes presented in Nourishing Traditions are designed to be made in small quantities in your own kitchen. They require no special equipment apart from a collection of wide-mouth, quart-sized mason jars and a wooden pounder or a meat hammer. (For special sauerkraut crocks that enable you to make large quantities, see Sources.) We recommend adding a small amount of whey to each jar of vegetables to ensure consistently satisfactory results. Concentrated whey and dried whey can be purchased at health food stores, but the whey you make yourself (pages 86-87) is far superior because it still contains its valuable enzyme content. Whey proteins are very fragile and easily denatured by the drying process.

About one inch of space should be left between the top of your vegetables with their liquid and the top of the jar, as the vegetables and their juices expand slightly during fermentation. Be sure to close the jars very tightly. Lacto-fermentation is an anaerobic process and the presence of oxygen, once fermentation has begun, will ruin the final product.

We have tried to keep the recipes in Nourishing Traditions as simple as possible without undue stress on ideal temperatures or precise durations. In general, a room temperature of about 72 degrees will be sufficient to ensure a lactic-acid fermentation in about two to four days. More time will be needed if your kitchen is colder and less if it is very warm. After two to four days at room temperature, the jars should be placed in a dark, cool spot, ideally one with a temperature of about 40 degrees. In days gone by, crocks of lacto-fermented vegetables were stored in root cellars or caves. A wine cellar or small refrigerator kept on a "warm" setting is ideal; failing that, the top shelf of your refrigerator will do. Lacto-fermented fruit chutneys need about two days at room temperature and should always be stored in a refrigerator.

Lacto-fermented vegetables increase in flavor with time—according to the experts, sauerkraut needs at least six months to fully mature. But they also can be eaten immediately after the initial fermentation at room temperature. Lacto-fermented vegetable condiments will keep for many months in cold storage but lacto-fermented fruits and preserves should be eaten within two months of preparation.

Throughout human history, bacteria and fungi have been intimately involved with both the success and failure of daily life. Microorganisms cause disease, but they also play a wider role in sustaining life. We know that certain bacteria play a major part in recycling chemical elements as well as compounds. For example, bacteria help return the materials of dead organisms back to the earth, so those materials can be used by living organisms. What's more, without bacterial action, living things would not be able to use certain compounds found in soil, water, and even the atmosphere. f, e. Modified versions of these microorganisms are now essential in modern day pharmaceutical production.

Fermentation is one of the oldest ways humans have used microbes. In his book From Caveman to Chemist, Hugh W. Salzberg retells some of the ancient history of fermentation. Since grains, fruits, juices, milk, and other organic liquids ferment naturally, some speculate that fermented drinks and dairy products must have been available not long after early people developed agriculture. The Bible refers to vineyards, wine, and the effects of too much alcohol consumption. Hannah, the mother of the prophet Samuel, was mistakenly admonished by the high priests to “put away thy wine from thee.” Ashurbanipal (668-626 BC), the last great Assyrian emperor, was something of an expert on wines. He compiled a list of what he considered the best wines. In ancient Egypt tax inspectors assessed the quality of the wines. Even poor Egyptians were sometimes buried with jars of beer. In both ancient Egypt and ancient Mesopotamia wines were put into jars at the place of origin in the presence of government officials and sealed with an official seal. In Mesopotamia, brewing was a home industry. The brewers were often women, who carried out the business of selling beer as well. These women-brewers had a relatively privileged position in society during the period of about 4000-2600 BC. The code of law handed down by the Babylonian lawgiver King Hammurabi (reigned 1792-50 BC) included regulations in terms of the sale price of beer and its minimum alcohol content. The brewer-women were also cautioned about allowing political conspiracies to be formulated on their tavern premises.

Fermentation is carried out by both bacteria (prokaryotes) and fungi (eukaryotes) during their metabolism. Both groups of organisms also figure in the world of human disease, as they are both sources of antibiotics, as we'll see throughout this module. Fermentation results in a number of byproducts that have many different uses. As mentioned, the most well-known product of fermentation is ethyl alcohol. This substance is both a beverage as well as a starter molecule for synthesizing other compounds. Since fermentation is carried out in the absence of oxygen, we call it an anaerobic process. It is a method by which organisms such as yeast obtain their energy by converting sugars into other chemical compounds, particularly carbon dioxide and water. Interestingly, our bodies also use this same anaerobic fermentation to obtain energy from sugars when oxygen is in low supply in our blood, such as during vigorous exercise. The products of this process are lactic acid and water rather than the carbon dioxide and water that human metabolism normally produces. In this day and age, pharmaceutical companies utilize the fermentation carried out by microorganisms to produce antibiotics, hormones,and specialized proteins such as antibodies and insulin. This wide range of products is possible because the bacterium or fungus involved in fermentation has been genetically changed to produce a specific substance.

You have the opportunity to explore fermentation as a chemical process through a series of activities linked below. The chemistry, although occurring in a living organism, can be examined outside a yeast or bacterial cell if you are able to extract certain enzymes (known as catalysts in the world of chemistry) from the cells. The fact that enzymes could carry out fermentation outside of a living organism was first shown by Eduard Buchner, a contradiction to the idea of Louis Pasteur that only living things could carry on the fermentation process. Buchner added sugar to juices extracted from yeast cells, even cells that had been killed by heating. Fermentation would begin within an hour. Buchner theorized that the yeast juice contained just one enzyme for converting sugar to carbon dioxide and water. Today we know that yeast cells contain more than a dozen enzymes involved in fermentation.

You don't need to understand the science of fermentation to make good spirits and liqueurs in the home unless you want to experiment with the fermentation system, i.e., fermenting larger volumes or higher alcohol levels. But know how is the base for improvements. If you read this whole document, you will know even more then most home brew shop owners (except those who also have read it)! Seeing fermentation from the yeast's perspective helps in understanding the science. Yeast is a living organism very similar to the individual cells in our own bodies. It is easy to think of dried yeast as "just another ingredient" like nutrients or sugar. Nothing could be further from the truth. Yeast's sole aim in life is to reproduce. It does this by " budding" to produce a daughter cell identical to the parent. Given a plentiful supply of oxygen, sugar, minerals, enzymes and amino acids, it will reproduce itself every 30 minutes and one thus ends up with a bucket full of yeast! Take away the oxygen and you get much less growth and a bucket full of alcohol. As far as the yeast is concerned, sugar (a sugar molecule) is a source of energy the yeast cell imports (eats). Glucose has 6 carbon atoms joined together by chemical bonds. It breaks these bonds one by one, each time liberating energy, which is then used for growth. Without oxygen, it can only break one bond and so liberates only a little energy (also little growth). What's left is thrown out of the cell as a waste product: ethanol. So, if you want to make alcohol, keep the oxygen out! To grow, yeast also needs amino acids, enzymes and minerals as well as the energy it extracts from sugar. l, a. These are needed to build new proteins (by creating bonds between amino acids) and carry out the many enzymatic reactions within the cell. A good Turbo sachet will contain all of these essential growth ingredients collectively we call these "yeast nutrients". If you have ever tried to ferment pure sugar with just yeast, you will know that you get very little alcohol, this is because yeast needs these other nutrients as well as sugar. So yeast is a living organism which uses sugar to make energy for growth. If there is no oxygen around yeast cannot extract all the energy from sugar and throws out ethanol as a waste product. To function, yeast also needs amino acids, enzymes and minerals, which collectively we call nutrients. As well as throwing out ethanol as a waste product, yeast throws out another 1300 other compounds, which we can call "volatiles". These volatiles fall into chemical categories

Silage Fermentation. Once oxygen is depleted in the forage mass, fermentation begins. Fermentation is the lowering of the pH in the forage to a point where no organism (mold or bacteria) can function. The pH is lowered by lactic acid which is a byproduct of lactobacillus bacteria. The lactobacillus bacteria are on the forage when it is mowed and multiply rapidly until the forage is fermented. Lactobacillus bacteria consume forage carbohydrates for their energy source and excrete lactic acid. The lactobacillus bacteria continue to produce lactic acid and lower the forage pH until they can not function anymore. At this pH level, the forage is fermented and can exist unchanged for many years as long it is not exposed to oxygen. f, h. Clostridia bacteria are also on the forage when it is mowed and are put in the silo with the forage. Clostridia bacteria consume forage carbohydrates, forage proteins, and lactic acid as their energy source and excrete butyric acid. Butyric acid is associated with rotten or putrefied silage. Situations that might benefit clostridia growth are insufficient forage carbohydrate levels (rain while forage is wilting, extended respiration period due to poor packing, seepage due to excessive forage moisture) to complete the fermentation process and/or low lactobacillus bacteria levels.

The debates over open versus closed fermentation will no doubt continue as long as there are interested brewers to debate. I intend to present some of my feelings, opinions, and experiences with using open fermenters, and point out some of the inherent pros/cons of using this technique. I want to emphasize one thing about this issue: the choice of fermenters is not going to be *the* deciding factor in your finished product, many other factors will play a more important part in the character of your beer. Namely, malt choices, mashing programs, and above all, yeast strain/viability/cleanliness will be the dominant influences on the finished beer. Having said this, there are instances where breweries who changed from open fermenters to closed unitanks have noted distinct changes in the perceived quality of the beers, when judged by experienced taste panels. [1] Open fermentation is a concept that most homebrewers think is a sure route to infected beer, or as something to be employed in some dark cellar in an old European brewery. I say nonsense! Think for a minute about some of the best world class beers and then think of how many are made using open fermenters: Sierra Nevada, Anchor, numerous English, Belgian and yes, even German brewers use them. It is a common sight in Bavaria to see a brewer mucking around in the thick krausen on top of the open fermenter, collecting samples, skimming yeast, generally doing things that homebrewers are told to avoid. Eric Warner has noted in his excellent book on Wheat beers that open fermenters are the preferred method of German weizen production [2], and that when open fermenters are used the yeast can be repitched for many more generations than when a closed fermenter is used.

So whats an open fermenter? At the simplest, it is a vessel with an open top. Depending on the size of the fermenter, they are often covered by some form of lid. The bigger versions are truly open, large shallow vessels, some are lined with stainless steel or an enamel like coating that is usually used over a concrete/block foundation. Often the fermenters are just large stainless steel cylinders. Most, but not all, have some form of attemperater device, to combat the temperature rise during ferments. This can be in the form of exterior jacketing, or metal piping that is immersed in the wort, cold water or glycol is pumped inside the pipes, cooling the ferment. Probably the most classic open fermenters are the Yorkshire Squares used at the Samual Smiths brewery in Tadcaster, England. These are made of flat slate walls, sealed together, with a collecting lid where the excess krausen is contained.

OK, so your thinking open fermentation only works in big breweries since they are filtering the air, and keeping the whole room under positive pressure, and nobody is allowed in. Yes, and no. Sure, lots of breweries go to the extreme of maintaining a separate room with filtered air. Lots more don't do anything. Certainly, the breweries in England that I visited never went to the extreme of filtered air, nor did the breweries in Bavaria and Belgium. Belgian methods of brewing may seem strange , but the dominant flavor profiles found in Belgium beers are a result of the choice of a yeast strain(s) that throws high levels of esters and phenolics, and rarely a result of some infection in the fermenter (even though this is the way to produce lambics, the word infection is a misnomer in this context). Certainly, the Bavarian brewmasters would recoil in horror if any foreign bacteria or wild yeast were to be found in the open fermenter, and in practice, they are not a problem.

I did not always use open fermenters, the first hundred or so of my beers were made with a "closed carboy" system. I put closed in quotes since the carboy can be fitted with a blowoff tube, resulting in a kind of hybrid closed/open fermenter. Since fall '92, I have been using a open fermenter exclusively, and I am a devoted fan of the concept. My fermenter is a stainless steel cylinder, of roughly equal height to width, with a heavy lid. If you brew with a 10 or 15 gallon stainless steel kettle, this can double as your fermenter, once you remove the hot break. Some brewers employ modified 1/2 BBl Sankey kegs, and these too make excellent open fermenters. I have also read of brewers modifying Golden Gate kegs and using these as fermenters. The least desirable, but easiest to start with, is the plain plastic bucket. The reason I say least desirable is that cleaning plastic is more difficult than stainless, and the inevitable scratches in the plastic walls can be harder to sanitize. Even so, I know of an award winning homebrewer who ferments in food grade plastic trash cans, and another 2 BBl brewpub who ferments in large High Density Poly- Ethelyne (HDPE) containers. I have found that as you increase the brew length (volume of beer produced), it is easier to fabricate some sort of fermenter that can hold the entire batch. In this way, you will be limiting the number of vessels to sanitize and clean up. It is far cheaper and easier to fabricate or modify a container to be an open ferementer than to make a closed one, particularly as the volume increases. An important consideration when sizing the fermenter is to account for a large amount of krausen that can develop during the ferment. Head space of 30% is optimum, but less can be used, with the result being some possible loss of product (which also occurs when using the blowoff carboy method).

Of course, there are some limitations to using open fermenters. I believe they are no more prone to infections than using carboys, but there is an increased chance for infection if one has numerous fruit flies or other animals around the fermenter, provided the lid is off. Probably the biggest limitation is that of time, I do not advise leaving the beer in the fermenter for more than 2 weeks. Of course, any ferment should be racked by the second week, so maybe this isn't such a limitation after all. The reason time is more important in open fermenters is not so much the proximity of the still beer to dead yeast, but of the danger of oxidation reactions occurring as the beer sits. In a closed system, this will not be a problem, but as long as the beer is moved in a timely manner, the CO2 produced during open fermentation will protect the beer. Another important factor to consider is the overall cleanliness of the fermentation area. It need not be sterile, but a reasonable degree of cleanliness is in order, in particular for fermentation inside of a refrigerator. Many brewers use a temperature control device to moderate the ferment temperature inside of a refrigerator. If you use an open fermenter inside of a refrigerator, be sure to clean all obvious sources of contamination and general dirt. Some may even want to sponge down the interior of the refrigerator with a mild sanitizer such as chlorine/water. At the very least, all spilled trub, yeast and wort should be thoroughly cleaned up. Household pets should also be prevented from crawling into the fermenting beer, they may like the results too much! My fermenter is located in the basement, a few feet off the ground, away from large drafts and any foreign debris sources.

Heres a summary of how I use my open fermenter. Since I use a stainless fermenter, I don't want to use a chlorine based sanitizer, due to problems with corrosion. So, I prepare a solution of Iodophor, at 12.5 ppm (1 oz in 10 gallons), of a few gallons. Using rubber gloves, I sponge the sanitizer over the sides of the fermenter. I let it run out the drain, then back over the sides of the fermenter. I also run Iodophor through my wort chiller into the fermenter, followed by a hot water rinse. Once the hot water is drained, the vessel is ready for cast out wort. I fill the fermenter from the wort chiller, oxygenate and add thick yeast slurry. As in any fermentation, there is no substitute for pitching enough viable clean yeast. d, c, l, e, d, j. The key to success with an open fermenter (or closed) is a sanitized vessel, and an adequate amount of pitching yeast. Remember to use significantly more yeast if the original gravity of the wort is higher than 1.060. If one is using enough yeast, visible fermentation is evident within 12 hours (ale wort, fermented between 60-70 F). As soon as the fermenter is full and the yeast is pitched, place the lid on. Once the fermentation is generating a thick head of krausen, I have found it helpful to leave the lid partially cracked, allowing an airspace for the large amounts of CO2 to vent.

With the ferment in high krausen, the classic dense rocky heads will form. At this stage, trub will be scrubbed from the ferment, and rise to the surface, along with other solid matter that was carried over into the fermenter. This scum can be skimmed off with a sanitized spoon (I leave a long handled stainless steel spoon in some Iodophor and just rinse it off when needed). The ability to skim the trub and yeast that rise to the top of the fermenter is one of the main advantages of open fermentation. Don't overdo it, but about once a day or every other day, depending on the rate of ferment, skim the top. Many ale yeasts tend to flocculate at the top of the ferment as the ferment diminishes. This yeast is excellent to skim and store in a sanitized container, in a cold fridge (as close to 32F as possible). When choosing yeast to save, be sure to wait a few days into the ferment so that the trub is scrubbed away and the harvested yeast is clean. As the ferment dies down, keep the lid over the vessel. Another great plus of open fermenting is the ease of dry hopping. What I do is let the main fermentation subside and when the yeast clumps to the surface, skim as much off as possible, then add the loose whole hops (I find that whole hops give better aroma and are easier to use with an open fermenter). Allow at least 3 days time for the dry hopping to take affect. I would avoid leaving the beer in the primary for longer than 2 weeks, and aim for 10 days when dry hopping, and a mere 5 days otherwise. These are optimum figures for ale ferments, and are often not realistic in homebrewing, the primary cause being inadequate oxygenation of the cast out wort, and/or insufficient yeast cell densities/viabilities in the pitching yeast. To rack off of the hops, use a sanitized copper/brass or stainless "choreboy" scouring pad, held over the racking cane with a rubber band. Alternatively, the hops can be removed with a sanitized strainer, provided a minimum of air is introduced to the still beer.

Fermentation is a two-stepped process that begins with the Putrefaction of the hermaphroditic "child" from the Conjunction resulting in its death an