Making Wine: Malolactic Fermentation

 One of the main problems arising after the end of alcoholic fermentation is represented by the biological stability of wine. At the end of alcoholic fermentation - or primary fermentation - wine is pretty fragile and without proper preventive measures, the probabilities faults of different nature may develop are very high. The chances of aging and keeping a wine depend not only by some components naturally found in it - such as alcohol, sugar, acid and polyphenols - but also by the biological stability, obtained by removing noxious bacteria and substances, as well as by avoiding the exposition of the wine at adverse conditions. One of the processes improving biological stability of wine is represented by malolactic fermentation, also known as secondary fermentation. Despite this process is useful for the stability of wine, it should be noticed in some white wines malolactic fermentation is generally avoided.

Casks and barriques are the containers generally used for malolactic fermentation

 The knowledge and study of malolactic fermentation is a pretty recent conquest, occurred in the course of 1900s. Since the 1600s, wine producers noticed a diminishing of acidity in “finished” wines, however they could not understand the cause. A significative step forward was done in 1800s, when they observed this diminishing of acidity corresponded to the disappearance of malic acid from wine, and only in the 1900s they will finally understand this diminishing was caused by specific bacteria having the capability of degrading malic acid into lactic acid and carbon dioxide. As during this phenomena is also developed carbon dioxide, it was defined as malolactic fermentation, that is considered as a fermentative process and bacteria responsible of this phenomena were defined lactic. Subsequent studies have proven malolactic fermentation is not a fermentative process: it is a process of enzymatic origin in which occurs the degradation of malic acid into lactic acid and this reaction has positive effects in some wines only.

 At the end of alcoholic fermentation - or soon before its natural end - the wine can look hazy, carbon dioxide is freed, it is observed a change in color and total acidity diminishes of about 0.5-1.6 grams per liter, up to about 4 grams per liter. These changes are the result of malolactic fermentation, a process which can take place soon after alcoholic fermentation - provided there are proper conditions - or in springtime, when the temperature raises. Temperature is in fact one of the factors determining the start of this process. Because of factors associated to stability, in general terms the start of malolactic fermentation is usually favored soon after the end of alcoholic fermentation, in order to both have a “finished” wine in a shorter time as well as to have a more stable wine according to a biological point of view. Before understanding how to favor the process of malolactic fermentation, let's understand what is this process and what are its effects on wine.

 As already said, defining this process as malolactic fermentation is improper, because it is not a fermentative phenomena, indeed it is a degradation of malic acid into lactic acid and carbon dioxide because of the action of lactic bacteria. These bacteria belong to many species, including Leuconostoc and Lactobacillus species. The action done by lactic bacteria, as well as the activation of their functionality, depends on many factors, in particular the pH of wine and temperature. When the right conditions take place, malolactic fermentation causes a biological deacidification of wine, with a decreasing of total acidity and the increasing of pH, usually from 0.1 to 0.2. According to an organoleptic point of view, wine will taste smoother - because of the presence of lactic acid, less aggressive than malic acid - and also aromas will be more complex and “ripe”. For these reasons, malolactic fermentation is considered indispensable for the quality of red wines, in which it is always favored.

 In case of white wines, malolactic fermentation will be done according to type and organoleptic qualities which are desired to keep or develop. As for dry white wines or rose wines, in which are generally kept both crispness of acidity and “young” aromas of fruit and flowers, it is recommended to avoid malolactic fermentation. In this type of wines, malolactic fermentation can be done - also partially - in case of excessive acidity, however part of aromatic freshness will be lost as well. Malolactic fermentation is sometimes done in some dry white wines destined to the aging in barrique, therefore making the wine “rounder” with “riper” and more complex aromas. Malolactic fermentation is however avoided in wines having a certain quantity of residual sugar because the activity of lactic bacteria could cause in the wine the development of lactic sourness - also called mannitic fermentation - caused by lactic bacteria which, by attacking sugar, transform it into acetic and lactic acid, with the development of a “sweet sour” taste in wine.

 There are many factors influencing the start of malolactic fermentation, including temperature, the main reason which impedes its development soon after alcoholic fermentation. In fact, after the end of alcoholic fermentation, in particular in cool climate areas, the seasonal lowering of temperature - followed by wintertime - impedes the start of malolactic fermentation which, in case there are proper conditions, will start in springtime, that is when the temperature will raise again. Temperature influences the speed of multiplication of lactic bacteria and the speed of the reaction. The optimal temperature for the start of malolactic fermentation is from 18 to 20° C (64-68° F). It is however indispensable the temperature is kept constant within this range and that does not however exceed 22° C (71° F), because this will develop volatile acidity. Over 30° C (86° F) its development will stop, whereas at temperatures lower than 15° C (59° F) its development will be very slow or it could stop as well.

 Sulfur dioxide, widely used in wine making, plays an important role in the activation of malolactic fermentation and its development. Lactic bacteria are more sensitive to sulfur dioxide than yeasts, therefore, when present in excessive quantities, malolactic fermentation can also not occur at all, also in case of the presence of the right conditions determined by other factors. It is believed a quantity of free sulfur dioxide greater than 10mg per liter impedes malolactic fermentation, whereas values lesser than 5mg per liter do not influence its development. Most of lactic bacteria are anaerobic, therefore their development and activity is favored in condition of absence of oxygen and in presence of carbon dioxide. For this reason, at the moment of the first racking, it is recommended to do this operation with no contact with the air and the container will be kept full in order to avoid the development of acetic bacteria and therefore the effects of sourness.

 Acidity of wine is another factor influencing the activation and development of malolactic fermentation. In case a wine has a pH value lower than 3.2 - therefore a very acid wine - the activation of malolactic fermentation will be very difficult and it is very likely it will not start at all. With pH values greater than 4.5 malolactic fermentation will have a very slow development. The optimal pH value is 4, however values of about 3.4 are considered to be favorable as well. In case a wine is too acid - therefore impeding malolactic fermentation - it will be necessary to diminish it, however it should be noticed this operation must be done after alcoholic fermentation. Deacidification of wine must be done by adding specific chemical products - in particular potassium bicarbonate - generally available in shop specialized in wine making.

 Despite this could sound superfluous, the activation and development of malolactic fermentation requires the presence of a sufficient population of lactic bacteria in wine. Lactic bacteria are naturally found in the bloom - the layer of waxy protective substance covering the skin of grape berries - therefore during the crushing of grapes they will be passed to the must. Some phases of the vinification, in particular during the operations about the adding of sulfur dioxide, could impede the activity of lactic bacteria, therefore making malolactic fermentation difficult. In these cases can be used two different methods, while making sure about the presence of all other factors favoring the development of malolactic fermentation. The first method consists in adding a wine in which malolactic fermentation is already active - therefore rich in lactic bacteria - whereas the second one consists in directly adding a culture of lactic bacteria, usually available in shops specialized in wine making.

 Before checking the development of malolactic fermentation, it is necessary it will start its activity. However, in wines requiring the development of malolactic fermentation, it is recommended this process to be done soon after alcoholic fermentation, without waiting for springtime, therefore ensuring the wine a better biological stability. At the end of alcoholic fermentation and after having done the first racking, we will begin to make sure about the presence of the factors favoring the development of malolactic fermentation, in particular temperature. Dependently on seasonal conditions, temperature could also be lower than 18° C (64° F), therefore it will be necessary to heat the room used for the production of wine. Despite home wine making does not allow necessary controls, it is however recommended to make sure about the presence of other favorable factors, such as the quantity of sulfur dioxide and pH, this latter value measurable with a specific instrument, therefore not very easy to do in our specific case.

 In case the conditions for the activation of malolactic fermentation are present but the phenomena does not start, it is very likely in the wine is not present a sufficient population of lactic bacteria. As already said, in this case it will be necessary to add a part of wine in which malolactic fermentation is active, or to add a culture of lactic bacteria in order to favor the start of the process. Lactic bacteria are usually available in freeze-dried form in shops specialized in wine making. Before adding bacteria it is necessary to proceed with their reactivation as it is indispensable they are added to the wine when they are in full activity. Reactivation methods changes according to the type of bacteria used, therefore it is recommended to read the instructions provided by the producer. When malolactic fermentation has started its activity, in the surface of the wine will be noticed tiny bubbles: it is the carbon dioxide produced by the degradation of malic acid into lactic acid.

 There are cases in which malolactic fermentation must be avoided, such as in case of white or rose wines in which it is desired to keep the freshness of aromas and a good acidity. The most simple method is not to favor the above mentioned conditions, however some of them could be dangerous for the health of the wine and may be cause of faults. The most practical and simple method is to add a proper quantity of sulfur dioxide to the wine, in order to avoid the activity of lactic bacteria. Another method consists in keeping the wine at a temperature lower than 18° C (64° F), in order to impede the activity of lactic bacteria. The best method however consists in using both methods, by adding sulfur dioxide after the end of alcoholic fermentation - in this specific case it is generally recommended a quantity of 8-10 grams per one hundred liters - while keeping the wine at a temperature lower than 18° C (64° F), in order to avoid, besides the other things, the development of negative tastes, such as mercaptan and sulphurated hydrogen.