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  Corkscrew Issue 47, December 2006   
Making Wine: the MustMaking Wine: the Must  Contents 
Issue 46, November 2006 Follow DiWineTaste on Follow DiWineTaste on TwitterIssue 48, January 2007

Making Wine: the Must

The production of the must represents the first stage of processing in the cellar, an operation which begins with the selection and crushing of the bunches of grapes

 The stage following harvesting consists in the production of the must, that is the crushing of the berries of grapes in order to get the juice that will be subsequently fermented into wine. Despite this operation could seem easy in its execution - the crushing of grapes is in fact an easy procedure - it must indeed be done in the best possible way in order not to compromise the quality of the grape and of its juice, by using - when needed - proper corrections. Of course, corrections done in the must depends on the quality of grapes: sound and quality grapes give a sound and quality must which does not require any correction. However, also in quality musts - and according to the type of wine to be made - it will be necessary to adopt proper precautions in order to avoid and prevent any alteration produced, for example, by the contact with oxygen. The goal of anyone who wants to make a good wine is always and however the same: to have sound and quality grapes in order to avoid as much as possible any kind of correction, both on the must and on the wine.


Ripe Trebbiano grapes ready to transformed into must
Ripe Trebbiano grapes ready to transformed into must

 According to a technical point of view, the must is the product obtained from fresh grapes - with or without stems and skins - by means of the mechanical procedures of crushing, draining and pressing. If we consider the must as the result of the crushing of grapes without using any other process, it is made of 80-85% pulp, 10-15% skins, 5% pips. During crushing - that is the operation consisting in the squeezing of berries - it is also generally done the so called destemming, that is the separation of stems in order not to excessively enrich the must with harsh tannins: an operation considered practically indispensable for the musts destined to the production of white wines. The must is the liquid fraction of the crushing of grapes - the juice - made of 70-80% water, 10-30% sugars (mainly fructose and glucose) as well as mineral and nitrogenous substances (inorganic and proteinic), polyphenols (tannins and coloring substances) and organic acids. The pomace is the solid fraction of the crushing of grapes and made of fibrous parts of the pulp, pips and skins.

 The analysis done in the must also detects the presence of yeasts, both because they are naturally found in the air, as well as - and in particular - they are found in the bloom, the opaque and whitish layer covering the skin of grape berries. Acid substances - even though they are not very perceptible at the taste because of the contrast action of sugar - generally have pH values from 2.7 to 3.5, indispensable for a regular fermentation process. In the must are also found vitamins of the groups A, B and C, mineral substances (potassium, calcium, magnesium, sodium, phosphates, chlorides, iron and copper) useful for a regular fermentation process and for the stability and limpidity of wine. Of particular importance is the presence of nitrogenous substances, indispensable to the development of yeasts responsible for alcoholic fermentation. These substances, at the end of fermentation, are transformed into aromatic components, some of them being very important in the overall aroma of wine. Despite their important role, the excessive presence of nitrogenous substances in the must can be cause of clouding in the wine as well as compromising its stability.

 

The Production of the Must

 Despite the crushing of grapes - the operation allowing the production of the must - is simple in its form, indeed it is important to use proper tools. In specialized shops are usually available many types of mechanical crushers allowing the crushing of large quantities of grapes and in pretty short times. The rapidity with which the grape is crushed is in fact of fundamental importance, as from the moment of harvesting to the time of the production of the must, it must pass the shortest possible time. One of the main problems in home wine making is represented by the procedure of separating the stems from the grape, an operation which is considered indispensable for the production of white wines. The crushing of grapes must be in fact preceded by destemming, that is the separation of the stems - the woody central part of the bunch to which are attached the berries - in order not to give the must excessive quantities of harsh tannins. On this regard, it should be remembered that in some cases, in particular when the grapes are poor in tannins, destemming can be avoided, however it is always suggested in the production of white wines in order to ensure a better finesse and elegance.


 

 This operation can be done by using a special machine - called destemmer - however it is more convenient and practical the use of a crusher-destemmer, that is a machine which besides separating the berries from the stem, crushes the grape as well. There are many types of crusher-destemmer available and not all are the same. A good crusher-destemmer machine, besides allowing the separation of the stems, will crush the grapes in a pretty delicate way, without excessive force and in order to not excessively tear skins while avoiding the breaking of pips. The work done by a good crusher-destemmer machine is easy to recognize: skins are intact and show only one side splitting and pips are perfectly intact. The breaking of pips must be avoided in particular in the production of white wines, as they give excessive quantities of tannins to the must. Intact skins will also facilitate the operation of the draining of must, that is the separation of the solid parts from the liquid part.

 According to the type of wine to be made, the must must be processed properly. In case of white wine, it will done the draining, that is the immediate separation of the skins and pips in order to limit the extraction of polyphenols. In case the must is destined to the production of red wine, skins are then allowed to macerate for all the fermentation process, or until it is not obtained the desired color or quantity of tannins. Soon after crushing, because of the contact with the air and of the presence of the yeasts naturally found in the skins, the must begins to oxidize and to ferment. Oxidation must be avoided in any case - as well as in the wine - whereas in the case of the production of white wine, it is recommended to delay the fermentation process in order to allow a proper sedimentation of the solid parts present in the must. In the production of white wine is in fact recommended the use of limpid must with no solid substance - made by the residuals of the pulp and skins - in order to get a more limpid and stable wine.

 Sulfur dioxide is very useful and fundamental in wine making soon after the crushing of grapes because, thanks to its effects, avoids detrimental oxidations, do a proper selection of yeasts and temporarily blocks their action. These two qualities will be indispensable for musts destined to the production of white wine, as they block the action of yeasts and provide a bland clarifying action, allow the sedimentation of the solid parts present in the must while delaying the fermentation. Despite sulfur dioxide has unwanted effects in the human body, the quantities typically used in enology can be considered relatively safe, however it is always and however recommended to use the least indispensable quantity possible. In home wine making, the most simple and reliable addition of sulfur dioxide is represented by potassium metabisulfite, simple to weigh and to add. On the contrary, it is not recommended the use of sulfur tablets to be burnt inside containers, as this method does not allow the correct measure of the quantity of sulfur dioxide added to the must or wine.

 When using potassium metabisulfite, it is good to remember it contains about 55% of sulfur dioxide, therefore one gram of potassium metabisulfite produces 550 mg of sulfur dioxide. Concerning the must, the quantities of potassium metabisulfite to be added can range from 5 to 30 grams per hectoliter, variable quantities according to the quality and soundness of grapes. In case of sound grapes and with no faults, it will be enough to add from 5 to 10 grams of potassium metabisulfite per hectoliter, whereas in case of grapes affected by mold, or even worse, in case they are rotten, it will be used from 20 to 30 grams per hectoliter. In normal conditions, the use of 10-15 grams per hectoliter can be considered correct in order to ensure a good fermentation. It is however good to remember the higher the quantity of sulfur dioxide used in the must, the slower the beginning of the alcoholic fermentation. Moreover, excessive quantities of potassium metabisulfite (50-60 grams per hectoliter or more) completely inhibit the fermentation of the must as in this way are eliminated all the microorganisms, including yeasts.

 The adding of sulfur dioxide, either in the form of potassium metabisulfite or other methods, must be done according to the type of the must. As the sulfur dioxide has solvent effects in some components found in the skin of the grape berries - in particular coloring substances and polyphenols - it is not suggested the adding, practiced by many, directly in white grapes as this would cause a not very desirable deep yellow color in the must. In case of must produced with white grapes, it is always recommended to add sulfur dioxide after the phase of draining, that is after having removed the skins from the must. In any case, no matter the type of wine to be produced - either white or red - it is recommended to add sulfur dioxide directly to the must while homogeneously stirring the mass. The contact with skins is indispensable in must obtained from red grapes as it will be the skins to give color to the wine, whereas in case of white wine, they will be separated soon after crushing. The drained part can be then pressed and added to the must, or it can also be used for the production of less valuable wines.

 

Analysis and Correction of the Must

 Despite we already analyzed the grapes in order to determine the right time of harvesting, before allowing the must to begin the stage of the alcoholic fermentation, it is recommended to do specific analyses in order to know its characteristics and - when needed - to do proper corrections. In home wine making it can be considered enough - as well as essential - the analysis of the quantity of sugar contained in the must, however it is important to analyze the quantity of acids as well. The analysis of the sugar contained in the must can be done by using a Babo densimeter or a refractometer, which gives the advantage of providing a more reliable result. In order to know the approximate alcohol by volume of the wine according to the quantity of sugar measured with the Babo densimeter or refractometer, readers are invited to read past articles about this subject.

 The analysis of acidity is more complex, in particular when done in the home wine making. In a glass container - preferably a Becher glass - are poured 7.5 milliliters of must to which are added 40 milliliters of distilled water and few drops of bromothymol blue. It is then added - slowly and while stirring continuously - sodium hydrate (NaOH) 0.1 N until the solution does not get a blue color, signaling all the acids found in the must have been neutralized (in red must will be noticed an evident clouding instead). The quantity of NaOH 0.1 N added, expressed in milliliters, will correspond to the total acidity of the must expressed in grams of tartaric acid per liter. The same method can also be used for determining the acidity of a wine. The correct quantity of acid in a must depends on the type of wine to be made.

 In case the must lacks of sugar or acidity, it is recommended to properly correct it. The increasing of the quantity of sugar in the must can be done either by adding concentrated must or common sugar, while remembering the latter method is forbidden in Italy for wines to be commercialized, whereas it is allowed in wines destined for personal consumption, such as the ones of home wine making. Each 1.7 kilograms of sugar added per hectoliter gives the increasing of the alcohol by volume of about 1%. The sugar must be diluted in few liters of must and then added to the mass in fermentation. The increasing of acidity in the must can be done by adding tartaric acid, usually available in enology shops. As tartaric acid tends to combine with some salts found in the must and in wine, each 1.3-1.5 grams of tartaric acid added per liter corresponds to the increasing of one gram per liter of acidity. Deacidification of the must is not recommended - saved the cases in which it is very high - as during alcoholic and malolactic fermentations, almost half of the original acidity is lost; therefore at the end of the production wine has probably reached the right acidity.

 




 Events  Share this article   Share on Google+   Summary of Corkscrew column Not Just Wine 
  Corkscrew Issue 47, December 2006   
Making Wine: the MustMaking Wine: the Must  Contents 
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