The term for alcoholic fermentation in the winemaking previously referred to the apparent "cooking" or "foaming" in the grape, Fermentation is the microbial degradation of organic matter without the inclusion of external electron acceptors such as oxygen ( anaerobically ) understood for the purpose of energy production. Organic substances can also be broken down with the inclusion of oxygen ( aerobic ) occur. For example, the acetic fermentation Oxygen is consumed, which is why it is not a fermentation in the scientific sense as described at the beginning. The term fermentation however, in German is an umbrella term for aerobic and anaerobic processes. This often leads to confusion because "fermentation" is used for alcoholic fermentation in other languages or because there is no separate term for it.
The process was long thought to be natural decay. The influence of air (even when oxygen was already discovered) was ignored. This is why the processes involved in converting must into wine, seasoning into beer and wine into vinegar called fermentation. The participation of microorganisms was by Louis Pasteur (1822-1895) recognized in 1857. Fermentation occurs everywhere spontaneous, where at an optimal temperature between 18 and 27 ° C yeast come into contact with aqueous sugar solutions. These are usually fruit juices, but other substances dissolved or added to water, such as cereals (barley, wheat, corn, rice), can also be used in the production of beer or other sugary substances such as potatoes.
The fermentation at Wine is mostly temperature controlled in stainless steel tanks In larger companies this is also done using computers. But also one barrel fermentation is used by many producers. For an optimal fermentation is a corresponding one beforehand must treatment Fermentation is the enzymatic breakdown of organic matter in anaerobic Environment, that is, in the absence of oxygen, If there is a higher concentration glucose (Dextrose) in grape can also in the presence of oxygen, ie in aerobic environment alcohol be formed. According to the English biochemist Herbert Grace Crabtree, this is also called Crabtree effect (or pasteur effect). An aerobic environment with oxidative Processes is also like in the production of certain wines port wine and sherry common.
The yeasts play a crucial role in fermentation. After this Press multiply in grape frenziedly fast through sprout and division. Towards the end there are 50 to 200 billion yeast cells per liter of wine. The biochemical processes are contained in the yeast enzymes controlled; for fermentation is the Zymase complex responsible. Natural or wild yeasts are widely available in the vineyard and elsewhere (air) and reach the cellar with the grapes. Through this, the fermentation can also be triggered completely independently, which was previously the custom. In this case one speaks of spontaneous fermentation, However, this is far more difficult to control, but is becoming increasingly particularly associated with Organic viticulture in the generation of Biowein prefers.
Mainly, however, pure breeding fermentation is still used, which is initiated using pure breeding yeasts (culture yeasts). These guarantee a quick, uncomplicated fermentation start . If necessary, this is done by starter cultures (also fermentation starter) supported. The most important yeast species involved in the beginning is Saccharomyces cerevisiae. The alcohol-sensitive types of yeast die quickly during fermentation. Only the alcohol-resistant survive until they too at 16 to 18% vol. alcohol content stop work. Newly developed "turbo yeasts" are used in the production of spirits today, which are even viable up to 20% vol. The sugar conversion is due to the yeast complex zymase caused multi-stage process. This is a special type of yeast in the production of certain Sherry types effective pile,
At the beginning of fermentation, the simple sugars are in the grapes or in the grape must glucose and fructose roughly equally. You will be 90% in ethanol and carbon dioxide converted in a ratio of 51:49, which is faster with glucose. Two molecules of ethanol and carbon dioxide are formed from one molecule of fructose or glucose. Arise as by-products aldehydes. ester. glycerin. methanol. Succinic acid. acetic acid. lactic acid. sulphurous acid. citric acid and higher alcohols respectively. fusel oil, as well as energy in the form of heat. Therefore the actual alcohol yield (ethanol) is not 51%, but only 47 to 48%. As a rule of thumb, 10 g of sugar per 1,000 g of must produce 0.66% vol alcohol.
The carbon dioxide is about fifty times the volume of the must and collects on the ground because it is heavier than air (relative density 1.52). There is therefore a risk of suffocation in the fermentation cellar and despite knowledge of this fact, some deaths occur every year. The one that used to be common candles sample, with which the oxygen content of the air should be checked, is unsuitable and life-threatening. Also the derivation over the usual ones Gärgitter can be dangerous if the fermentation room is lower than the cellar entrance. Today, the carbon dioxide is extracted via exhaust doors (ventilators) and taken outside or also used in large wineries. To a small extent, the carbon dioxide is bound in the wine, which also creates real ones carbonic acid, In the manufacture of sparkling wine is as fine as possible or high bubbles Perlfähigkeit primary goal.
An important criterion is the fermentation temperature . Fermentation is stormy at higher temperatures and slow at lower temperatures. The optimal temperature for the multiplication of the yeast is 25 ° Celsius. The "correct" fermentation temperature depends on the desired type of wine. The warmer it is fermented, the more flavors and alcohol are lost, but more among other things glycerin educated. It also ensures safe fermentation with the result of a dry wine. It should be noted that the must warms up more in larger containers (600 liter containers up to 22 ° C, 7,000 liter containers up to 33 ° C). In preparation, the pre-clarified must is brought to a starting temperature of around 15 to 18 ° Celsius. From one especially to White wine usual cold fermentation Using special cold proofing yeasts one speaks at temperatures from 10 to 15 ° Celsius.
At the at red wine usual maceration higher temperatures are required, which are between 25 and 30 ° Celsius. If the fermentation temperature is too high from 35 ° Celsius, Versieden come what the vinegar sting and can spoil the wine. Cooling is required to maintain the desired temperatures. This is often done with cool and heatable fermenters automatically controlled by computer. These are mostly out stainless steel or ceramics. The fermentation time is between eight days and six weeks, depending on the temperature, yeast and type of wine. For special wines such as B. Vin Santo, it can take months. For an optimal fermentation process , too Gäraktivatoren added.
The fermentation takes place in three phases. During the fermentation phase , the yeast sprouts and multiplies, whereby carbon dioxide is already formed. This is followed by stormy fermentation (French bouillage), which is characterized by a large increase in yeast, carbon dioxide formation and heat development; the must can literally simmer. In the quiet post-fermentation phase , the last sugar residues are broken down and valuable taste and flavorings educated. Do you want a specific one residual sugar must undergo fermentation at this point clocked become. This is done either by cooling down to minus 3 to 2 ° C, by adding sulfur, by short-term heating to 75 ° C or by certain wines Spriten (Addition of pure alcohol). Depending on the cellar temperature, must temperature or sugar concentration, the yeasts can stop working early. An unwanted end of fermentation ( getting stuck ) is one of the most common Gärfehler,
The fermentation ends when the sugar is almost completely converted, then the yeast has no more food. The second main reason is when the conditions have reached a hostile status for the yeasts, for example the alcohol content. A complete fermentation of the sugar is not possible in a natural way, however, even with completely dry aged wines, a certain amount of residual sugar remains in the wine. The dead yeasts together with other substances than Trub from the bottom of the fermenter. Now it has to be decided whether the most common one for making red wine malolactic fermentation (BSA = biological acid degradation) takes place or should be approved.
If the acid is to be retained in the wine (which can make sense in warmer regions), this is prevented by removing the necessary proteins. There is ever a question of whether acid should be added or broken down growing zone or country-specific different legal provisions (see under leavening and deacidification ). After fermentation is complete, the wine is left on the lees for a longer period for certain types of wine in order to give it more taste and fullness and also carbonation. This is known as lees (French: sur lie = storage on the lees respectively. whole yeast ).
Various forms of fermentation have been developed in recent decades. The main goal is an intense one extraction, that means getting as many colors and flavors out of the grapes. There are a myriad of techniques and procedures:
From the amount left over after fermentation residual sugar in the wine there are the tastes defined by wine law; see under sugar content, Complete lists of the numerous cellar techniques, as well as the wine, sparkling wine and distillate types regulated by wine law are under the keyword winemaking contain. There is extensive wine law information under the keyword wine law,