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Basic requirements for wine manufacturing:
• Land: 1 acre
• Electricity: 200hp
• Manpower: 20 to 25
Raw material requirements:
• Grapes and other fruit, yeast
• Raw material requirements
• fermentation and storage vats
• fixed and moveable pipes and hoses
• refrigeration equipment
• barrels, if utilised
• bottling line, if wine is to be bottled on the property
• Laboratory equipment
• Cleaning equipment.
Red Wine Making:
This chapter describes the process of wine manufacturing.
Various approaches can be, and are, taken in the wine manufacturing and many different processes may be used. The following
processes are usually undertaken, but it should be borne in mind that the list is neither prescriptive nor exhaustive.
1. Desteamming and crushing
On arrival at the winery, the stalks may be removed to prevent any bitterness tainting the juice. Following this, the grapes canbe lightly crushed. Both these tasks can be performed by the same machine, a crusher–distemper, The grapes are fed via a hopper into a rotating slotted cylinder. As this rotates,the berries pass through the slots, leaving the stalks behind – these are then expelled from the machine and can be used for fertiliser.
The grape berries are passed through a series of rollers that can be adjusted to give the chosen pressure in order to release the juice. For certain wines, where whole bunches are required for pressing, e.g. Beaujolais, the grapes will not be destemmed or crushed. There is a growing trend amongst some red wine makers to include at least a percentage of whole grapes in their fermentations.
2. Must preparation
The resultant mixture of grape juice with seeds, skins and pulp (must) now has to be prepared for fermentation. Various additions and adjustments may be undertaken.
• Sulphur dioxide (SO2): this is the winemaker’s universal antioxidant and disinfectant, and is used at many stages in wine manufacturing. To prevent fermentation starting prematurely, it may be added to inhibit the action of wild yeasts and bacteria.
These organisms require oxygen for growth, and are naturally found on grape skins. Wild yeasts (which can cause off flavours)die when 4% alcohol is reached. Naturally occurring wine yeasts found in the vineyard and the winery work without the action of oxygen and thus can work even if the must is blanketed with sulphur dioxide. In many parts of the world, winemakers now prefer to use selected cultured yeasts for greater control, reliability and for specific flavours. It should be noted that producers often speak of wild yeast fermentation, when refer-ring to use of the natural yeasts that come into the winery on the grapes.
• Must enrichment (chaptalisation): in cooler climates, grapes often do not contain enough sugars for a balanced wine manufacturing. This may be addressed by chaptalisation – the addition of sucrose to the must or the juice in the early stages of fermen- tation. It is important that only the minimum necessary amount is added or further imbalance will be created. The practice is not permitted in many, hotter, countries. The European Unionis divided into zones according to crude climatic conditions, and the amount, if any, of chaptalisation allowed variesaccording to the zone. In some countries concentrated grape must is used instead of sugar.
• Acidification: this may be necessary if the pH of the must is too high, that is, if the acidity is too low. The addition of tartaric acid is the usual method employed. The addition of malic acid is not permitted within the European Union, although it is not uncommon in Argentina. Acidification is gen- erally not permitted in cooler regions of the European Union (classified in the EU as regions A and B), but derogations are possible. For example, in 2003 Regulation (EC) No. 1687/2003 permitted acidification on account of the exceptional (hot) weather conditions.
• De-acidification: this may be necessary if the pH of the must is too low. It is not permitted in warmer regions of the European Union. There are a number of materials that may be used, including calcium carbonate (CaCO
3), perhaps better known as chalk, potassium bicarbonate (KHCO 3), and potassium carbonate (K 2CO 3). Another agent that may be utilised is Acidex ®, which is a double-salt seeded calcium carbonate designed to reduce both tartaric and malic acids in must or wine. The product was developed in Germany, where the cool climate often produces grapes of high acidity. NB: Calcium carbonate only reduces the tartaric acid.
• Yeast: cultured yeasts may be added, or the winemaker may simply utilise the natural yeasts present on the skins.
• Yeast nutrients: as living organisms, yeasts need nutrients, and B group vitamins may be added to promote their growth.
• Diammonium phosphate (DAP): this may be added, usually at a rate of 200 mg per litre of must, to help ensure that all the sugars are fermented out and to stop the formation, during fermentation, of hydrogen sulphide (H 2S), which is most undesir- able. Its use is common in New World countries, particularly when the musts are nitrogen deficient.
• Thiamine: thiamine (vitamin B 1) may be added in the early stages of fermentation to help increase yeast populations and prolong their life. The yeast Brettanomyces is regarded by most as a spoilage yeast and, therefore, is generally undesirable.
It needs thiamine to grow, and additions of this need to be undertaken with caution.
3 Fermentation, temperature control and extraction
As we have seen, the process of fermentation results in the conversion of sugar by the enzymes of yeast into alcohol and carbon dioxide.
The fermentation of red wine takes place with grape solids present, in order to extract colour from the skins. Initially the fermentation can be very tumultuous, but as more sugar is converted, the rate slows down. In the majority of cases the fermentation is continued until the wine is dry or off dry, and depending upon the richness of the must, the final alcohol concentration is generally in the range 11% to 14.5% by volume.
• Temperature control
The fermentation process is a turbulent one and creates heat naturally. During red wine manufacturing, fermentation may begin at about 20 °C, but temperatures may rise to 30° to 32 °C. Yeast ceases to work if the temperature rises above approximately 35°C. Therefore some form of temperature control may be necessary, especially in warmer regions, to prevent this happening before the sugars are fully fermented. It is only in the past few decades that wine- makers have had the equipment and ability to be able to have real control. One hundred grams of sugar in a litre of juice has, when fermented, the theoretical potential to heat the juice by 13 °C. If grape must of 11.1° Baumé commences fermentation at 15 °C, the potential tem- perature increase could be to 41°C. If fermentation of must with a Baumé of 14.5° commences at 20°C, the potential temperature increase is to 54 °C. Of course, some of this heat is naturally dissi- pated during the period of fermentation through the walls of the vat and with the rising carbon dioxide, through the juice to the surface. Good colour extraction requires warm fermentations. However, cooler fermentations aid the growing of yeast colonies and give higher alcoholic degrees. The warmer the temperature, the less time thefermentation takes. Accordingly, managing the temperature can be quite a tricky exercise. A winemaker may decide to start a vat fairly cool, at say 20 °C, and allow it to rise naturally to around 30 °C to aid extraction. In the latter stages, the vat may be cooled to 25 °C or so, to ensure complete fermentation to dryness. In the cool underground cellars of regions like Burgundy, the temperature of small vats or barrels can be self-regulating. Cooling equipment may be required for larger vats. Wine can be pumped through heat exchangers to reduce (or increase) temperature. Stainless steel tanks are now commonly wrapped with water or glycol cooling jackets. Alternatively, they may be cooled by showers of cold water running down the outside. In concrete or wooden vats a metal cooling device (drapeau) can be inserted or built in.
The traditional process for red wine manufacturing is for the grape mass to be fermented in open vats. The solids and skins rise to the surface with the CO 2 and create a floating cap. This is a disadvantage because the skins need to be in contact with the juice for there to be good extraction of colour and tannins. Also, acetic bacteria thrive in such a warm, moist environment, risking spoilage of the juice.
Consequently, during the process, the juice is drawn out from near the bottom of the vat and pumped up and sprayed over the cap to submerge it. This process, known as remontage, has the additional benefit of aerating the must, which helps to boost the yeast colonies. This technique of pigeage, simply punching down the cap, is used for some varieties, particularly Pinot Noir which needs a very gentle extraction process. Although vats can now be fitted with mechanical pigeage equipment, in many wineries submerging the cap is done by hand with wooden paddles, sticks, or even the feet of the cellar staff precariously suspended over the fermentation vats.
Depending on the style required, the wine may be left to soak with the skins after completion of the alcoholic fermentation, untilsufficient colour, flavour and tannins are extracted. This maceration could vary from 2 or 3 days up to 28 days. If an ‘early drinking’ red is required, the juice may be drained off the skins just before completion of the fermentation. Alternatively, if the winemaker believes that a post-fermentation maceration would not be beneficial, with the risk of hard tannins being extracted, the tank may be drained hot, that is, immediately after the alcoholic fermentation, before the wine has cooled.
Racking is the process of transferring juice or wine from one vessel to another, leaving any sediment behind. After the fermentation and any maceration the wine, known as free-run juice, will be run off to another vat. The skins and other solids are left behind in the fermentation vat. These will be transferred to the press to obtain further juice. Between 10 and 15% of the total juice comes from the pressing process. Free run juice has less tannin and is usually considered superior to pressed juice. Some producers choose to make their wine only from free run juice. Racking will also take place at various other times in the winemaking/maturation process to remove the wine from lees and sediment, and clarify it. Aeration can also take place during the racking process, and an addition of sulphur dioxide may be made if necessary.
The juice released from the press will naturally be higher in tanninand colouring pigments. More than one pressing may be carriedout, but with each pressing the press wine becomes coarser. Some presses are controlled to exert varying levels of pressure at different stages, often gentle at the beginning but harder with each subsequent pressing. There are a variety of types of press available, including basket press, horizontal plate press and pneumatic press. The characteristics of these will be consideredlater.
7 Malolactic fermentation
This usually follows the alcoholic fermentation and so is sometimes referred to as secondary fermentation. Yeast is not involved. It can be described as a transformation caused by the action of strains of bacteria of the genera Lactobacillus, Leuconostoc and Pediococcus.
Harsh malic acid (as found in apples) is converted into softer tasting lactic acid (as found in milk). One gram of malic acid produces 0.67g of lactic acid and 0.33 g of carbon dioxide. Malolactic fermentation can be induced by warming the vats, or inoculating with strains of lactic acid bacteria. Alternatively, it can be prevented by treating the wine with sulphur dioxide and/or keeping the wine cool. It gives the wine a slight ‘buttery ’ and/or toasty nose and sometimes a certain amount of complexity.
This is an important operation in wine manufacturing. Once fermentation has finished there will be various vats or barrels containing wines from different vineyards, sections of vineyards, districts or even ages of vine. Individual grape varieties, having been picked according to ripeness, will have been fermented separately. Blending of these various vats will then take place in order to achieve the desired final style and quality of wine. The prime reasons for blending are to have a product that is greater than the sum of its parts, to even out incon- sistencies and perhaps to maintain a brand style.
This selection process could involve a great number of component parts. Where different grape varieties are blended together, the winemaker considers what proportion of each variety is included in the blend. Some varieties or vineyard blocks may perform better in a particular season. Where high quality is the object, some vats may well be rejected and used in a lower quality wine or sold off in bulk.
Immediately after fermentation, wines may taste rough and fairly unpleasant. A period of maturation is required during which thetannins soften and acidity levels fall. The choice of maturation vessel and the period of time depend upon the style of wine to be produced and quality and cost factors. There are many types of maturation vessels, including stainless steel vats and wooden barrels.
Some wines which are intended for early drinking, such as inexpensive or branded wines, need little or no maturation. Stainless steel is an ideal storage material because it is impermeable to gases such as oxygen. The wine therefore is stored until required for bottling. Of course, stainless steel is ideally suited to temperature control and is used where long-term, oxygen-free storage is required, for example when inexpensive wines are held prior to being ‘bottled to order’. Most high quality red wines undergo a period of barrel maturation – usually somewhere between 9 and 22 months. During the time in barrels, the wine will undergo a controlled oxygenation and absorb some oak products, including wood tannins and vanillin. Barrel size has an effect on the maturation of the wine; the smaller the barrel the quicker the maturation. Temperature also plays an important part; the lower the temperature, the slower the maturation. When the barrels have been filled they will be tapped with a mallet to dislodge air bubbles, which rise to the surface of the wine, thus removing oxygen. During the period in barrel the wine will be racked several times to aid clarification – for example red Bordeaux wines are normally racked four times during the first year’s maturation, and perhaps once or twice in the second. Many producers regularly top up the barrels to replace wine lost to evaporation, but there is a viewpoint that if the barrels are securely sealed the ullage at the top is a partial vacuum and topping up may not be beneficial. The processes of preparing the wine for bottling will be considered later.
10) Dry White wine manufacturing:
Although the techniques used for making white wine are similar to red, the sequence of operations is different.
10.1 Crushing and pressing
On arrival at the winery, white grapes should be processed with minimum delay to avoid deterioration and the onset of premature fermentation. In hot climates, ideally grapes are chilled before the crushing stage. In most cases, they will be destemmed and lightly crushed before pressing. It is becoming increasingly popular for the winemaker to allow some hours or even days of skin contact with the juice at low temperatures before the grapes go to the press. This may extract more aroma compounds and enhance flavours.
When white wine is being made from black grapes, crushing must be avoided to prevent any colour being leached into the juice, and whole clusters are sent to the press. Many winemakers like to do this with clusters of white grapes too, believing this gives a great purity of juice.
Unlike in the red wine process, pressing occurs before fermentation. Gentle pressing, avoiding the crushing of pips, results in better quality juice. The skins of white grapes are not used during the fermentation process.
10.2 Must preparation
The juice is drained from the press into settling tanks. If the must is not cleared of solid matters, then off tastes can result. A simple settling over a period of 12 to 24 hours, a process known in France as débourbage, may take place. The must is then racked to another tank for fermentation. Clarification can also be achieved by using a centrifuge, which speeds up the process, or by filtration. Very fine particles can also be removed by treating the must with bentonite.
This is a form of clay earth which acts as a flocculent, attracting and binding fine particles which then settle out of suspension. If the must is over clarified, fermentation may proceed slowly and the wine may not ferment to completion. Yeast nutrients attach to solid matter within the wine, making them accessible to yeasts. The removal of solid matter can reduce the availability of nutrients, with detrimental effects on yeast growth.
The must may then be passed through a heat exchanger to lower the temperature. This not only prevents a premature onset of fermen- tation, but also preserves freshness and flavours. The most is treated with sulphur dioxide to prevent aerobic yeasts and spoilage bacteria working. Selected cultured yeasts may then be added.
The must is then pumped directly to the fermentation vats or barrels. With careful winery design, this process can be achieved simply by gravity, and for pumping is by nature a harsh process. Selected cultured yeasts may be introduced and are often used in white wine making.
White wine is usually fermented cooler than red wine, at around 10° to 18°C and over a longer period to preserve primary fruit flavours. Each vat is under temperature control, usually with its own chilling system. Cool fermentations are desirable for aromatic whites, with less cool fermentations used when full-bodied wines are desired. Some white wines are fermented in barrels to give particular charac- teristics to the wines and a better integration of oak flavours. Barrels also give a better supply of oxygen, required by the yeast in the early stages of fermentation. The choice of new or used oak from particular origins will have been made. It may be that different lots are fermented, for example, in new, second fill and third fill oak barrels and blended together at a later stage. After fermentation, the wine may be left on the lees which, from time to time, may be stirred. This operation is known as bâtonage and gives a yeasty, and perhaps creamy flavour to the wine.
Vat matured wines may also be left lying on the lees. We should distinguish between the gross lees, the large lees from the fermen- tation pre-racking, and the fine lees that will fall after the wine has been racked for the first time. Ageing on lees may take place on either gross or fine lees, depending on the textures sought. Stirring of lees may also take place in vat – a ‘propeller’ type of device may be inserted through the side of the vat to rouse the settled sediment. It should be noted that some varieties (e.g. Chardonnay) may benefit with lees stirring, whilst others (e.g. Riesling) will suffer if the lees are roused.
10.4 Malolactic fermentation
Malolactic fermentation may follow alcoholic fermentation to soften any aggressive acidity. Some white grape varieties, e.g. Chardonnay, work well with malolactic fermentation, whereas others may not. Other varieties which are valued for their crisp acidity, such as Riesling or Sauvignon Blanc, do not usually undergo malolactic fermentation. Also, in some countries the crispness of wines that have not undergone the malolactic fermentation is a desirable feature. For example, a Sancerre from the Loire Valley in France, a wine made from Sauvignon Blanc, can be much appreciated for its lively acidity. Following the malolactic fermentation, the wine is racked into clean vats or barrels.
Much white wine is stored in stainless steel or concrete vats until ready for bottling. It is important that oxygen is excluded, and the vats should be kept either completely full or blanketed with nitrogen or carbon dioxide. Even if white wine has been fermented in barrel, it may be that it continues its maturation in barrel, too, to obtain more oak flavours.
11) Preparing Wine for Bottling:
To ensure that wine is of the clarity expected and remains stable in the bottle for its life, various treatments may be undertaken; however, many makers of fine wines believe treatments should be kept to a minimum. We have already seen that racking is one of the operations necessary to achieve clear wine and to reduce the risk of off flavours. It is important for the wine to be protected from oxidation during the racking process, and vats or barrels may be sparged with inert gases to achieve this. A number of operations may be undertaken to ensure the clarity of wine.
With the coarse sediment removed by racking or centrifuge, there remains other lighter matter suspended in the wine known as colloids. These are capable of passing through any filter. If not removed they will cause the wine to look ‘hazy’ and then form a deposit.
The colloids are electrostatically charged and can be removed by adding another colloid with the opposite charge. Examples of such fining agents are egg whites, gelatine, isinglass (obtained from swim bladders of fish) and bentonite. Quantities need to be carefully controlled otherwise the fining agent itself will form a deposit, or a further, opposite, electric charge may be created.
Fining may also be used to remove excess tannin and so improve the taste of the wine. Phenolic compounds are absorbed by the substance PVPP (polyvinylpolypyrrolidone). This may be used at the fining stage to remove colour from white wines and help prevent browning.
Filtration is the process used to remove solid particles, and may take place at various stages in winemaking, for example must or lees filtration. However, one of its main uses is in the preparation for bottling. The processes of fining and filtration are not interchangeable. Filtration requires care and expertise. Today, some winemakers choose to use minimum filtration to avoid what they see as
‘Stripping the body’ away from the wines.
There are three principal categories of filtration, which may be used at different stages in the winemaking process:
11.2.1 Earth filtration
This filtration method is used for initial rough filtration and can remove large quantities of ‘gummy’ solids, which consist of dead yeast cells and other matter from the grapes. The filtration takes place in two stages. Firstly, a coarse grade earth called kieselguhr, which is commonly used as the filter medium, is deposited on a supporting screen within a filter tank. A mixture of water and kieselguhr may be used to develop the filter bed. This is known as percolating. Secondly, more earth is mixed with wine to form slurry that is used continuously to replenish the filtration surface through which the wine passes. Wine is passed through the filter and the bed gradually increases in depth. Eventually it will clog and the kieselguhr will have to be completely replaced with fresh material.
The rotary vacuum filter consists of a large horizontal cylinder or drum with a perforated screen covering the curved surface. A filter cloth is stretched over the curved surface. The cylinder rotates in a trough which contains initially kieselguhr and water. A vacuum is drawn on the cylinder and the kieselguhr–water mix is drawn onto the cloth. The water is drawn into the cylinder, leaving a layer of kieselguhron the cloth to act as a fine filter medium. Wine is fed to the trough and filtered through the kieselguhr. As the surface fouls, more kieselguhr can be added to the wine to replace the fouled layer, which is scraped off by blades as the cylinder rotates. A sophisticated filter is found in the totally enclosed rotary vacuum filter, which reduces the risk of oxidation damaging the wine, but with this type the fouled earth has to be removed manually.
11.2.2 Sheet filtration (sometimes called plate and frame filtration)
A series of specially designed perforated steel plates are held in a frame. Sheets of filter medium (cloth or paper) are suspended between the plates, which are then squeezed together by screw or hydraulic methods. The filter sheets are available with various ranges of porosity. Wine is pumped between pairs of plates to pass through the filter sheets into a cavity in the plates and then to exit the system. Yeast cells and other matter are trapped in the fibres of the filter media.
11.2.3 Membrane filtration
If undertaken, this is the final filtration process and used just before bottling. The wine needs to have been well clarified by other filtration methods before using this process. Membrane filters are constructed of plastic or ceramic materials which are porous to water and com- pounds of small molecular size, e.g. alcohol, colour and flavour compounds found in wine. Large compounds such as proteinaceous materials will not pass through. Wine is passed under pressure across the membrane surface to filter through, leaving undesirable materials trapped on the membrane. The process is not used for full-bodied red wines as it can reduce body and flavour.
Stabilisation may be carried out to prevent tart rate crystals forming after the wine has been bottled. The tart rates are either potassium or calcium salts of tartaric acid and are totally harmless. They are sometimes found on the cork or as sediment in the bottle, and sometimes cause unwarranted concern to consumers. To inhibit the precipitation of tartrate crystals in bottle, the wine is chilled to -4°C, or colder in the case of liqueur (fortified) wines.
After approximately 8 days the crystals will have formed, and the cleared wine can be bottled. Another method of removal is to reduce the temperature of the wine to approximately 0 °C and seed it with finely ground tart rates, followed by a vigorous stirring. The seeds then attract further crystals to them and the entire process of removal takes just 24 hours or so.
11.4 Adjustment of sulphur dioxide levels
As we have seen, sulphur dioxide is the winemaker’s generally used antioxidant and disinfectant. However, only a percentage of the sulphur dioxide in the wine, the ‘free’ SO2, acts in this way. The other proportion becomes ‘bound’ with the wine and is inactive. Before bottling, the free SO2 levels should be adjusted to between 25 and 35mg/l. Higher levels are needed for sweet wines to inhibit further fermentation of the sugars.
A number of treatments may be carried out immediately prior to bottling to ensure the wine’s final stability. These include pasteurisation or sterilisation. Four systems of treatment are available to the producer and use is dictated by the wine’s specification.
• Cold sterile filtration: this process does not utilise heat. The wine is filtered through fine sheets or a membrane filter to remove all yeast cells. It is then aseptically bottled in a sterile environment. The method is particularly suitable for wines containing residual sugar and with modest alcohol levels. Such wines would otherwise risk re-fermentation in the bottle.
• Thermo tic bottling: the wine is heated to 54°C and bottled hot. At this temperature the yeasts are killed, and the alcohol becomes toxic to any bacteria.
• Flash pasteurisation: the wine is heated to 95 °C for one or two minutes, then rapidly cooled and bottled cold.
• Tunnel pasteurisation: the wine is bottled cold, and then passed through a heat tunnel where the sealed bottles are sprayed with hot water to raise the temperature to 82°C for 15 to 20 minutes.