Specific Options for Red Winemaking Flashcards
What factors affect extraction of anthocyanins, tannins and flavours from the grape skins?
- temperature – higher temperatures result in greater extraction
- time on skins – generally, the longer the juice/wine remains in contact with the skins the greater the extraction
- management of the skins and juice – the more the skins are mixed through the juice, the greater the extraction
- the medium in which the extraction is taking place – for example, tannins are most soluble in alcoholic solutions (e.g. wine), whereas anthocyanins are most soluble in aqueous solutions (e.g. grape must).
Explain maceration before fermentation?
The key aim of maceration before fermentation is to extract colour and flavours, without extracting tannins. Anthocyanins are soluble in both the must and wine, whereas tannins are more soluble in alcoholic liquids, and are therefore not readily extracted at this point in the winemaking process.
Cold soaking
Cold soaking is also known as cold maceration or simply pre-fermentation maceration. The juice and skins are typically chilled (to around 4–10°C / 39–50°F) to reduce the rate of oxidation, microbial spoilage and spontaneous fermentation. It is typical for pre-fermentation maceration to last 3–7 days, usually with the use of punching down and/or pumping over to mix up the skins and juice, aiding extraction (see Maceration During Fermentation). This also avoids the growth of spoilage microbes that need oxygen, such as acetic acid bacteria, on the top of the cap of skins. Cold soaking is a gentle technique, suitable for premium wines. The cold temperatures result in a slow extraction, which can easily be monitored and controlled to achieve the level of extraction desired. It is very commonly conducted on Pinot Noir to promote colour intensity, because this grape variety has a low level of anthocyanins, but is also used for other grape varieties if the winemaker wants to promote colour extraction without risk of extracting high levels of tannin. There is a cost to cold soaking in the energy required to chill the wine. Also, time taken for cold soaking (tying up valuable tank space) means that it is often not suitable to produce high-volume, inexpensive wines.
Macerations using heat
As previously stated, higher temperatures lead to greater extraction, and therefore the following techniques are designed to extract high levels of anthocyanins and flavours quickly. (Some tannins may also be extracted, but to a lesser extent.) Two key techniques are flash détente and thermovinification. Thermovinification involves heating the must to around 50–60°C (122–140°F) and sometimes higher. The time spent macerating at this heat can range from a number of minutes to several hours; generally, the higher the temperature, the shorter the maceration. In flash détente, destemmed grapes are quickly heated to 85–90°C (185–194°F) and then rapidly cooled under a vacuum. This process takes place in as little as two minutes. (The short time at high temperatures limits the risk of ‘cooked’ flavours developing.) The process bursts the cells in the grape skins, allowing a very rapid extraction of anthocyanins and flavours. The vacuum system is expensive to buy, and it therefore tends to be used at high-volume wineries where the large throughput may justify its cost.
With both techniques, the juice may be pressed off the skins before fermentation if a low tannin, fruity style is desired. However, the wines produced in this way tend to have issues with colour instability. This is because there is not enough tannin to bind with the anthocyanins and form more stable compounds. This process is therefore often used for inexpensive or mid-level wines that are going to be consumed shortly after production. It may also be used as a blending component in higher quality wines, bringing juicy, fruity flavours to the blend. Alternatively, the juice may be fermented for a period of time on the skins if a style with more tannin is required.
Both flash détente and thermovinification can be particularly beneficial if the grapes are affected by botrytis (grey rot), as the high temperatures denature oxidative enzymes (called laccase) produced by the rot. Flash détente can also be used as a treatment for smoke taint. Both techniques are said to intensify the fruitiness of the wines, but critics of these techniques feel that this can lead to a reduction in more subtle varietal characters.
Explain maceration during fermentation and the different cap management techniques?
The vast majority of red wines are fermented on the skins. It is important to mix the skins with the juice or wine during fermentation for a number of reasons. In a tank of fermenting must, the grape skins typically float at the top of the liquid, buoyed by carbon dioxide. This forms what is known as a cap. Without mixing, this would mean that the skins spend the fermentation macerating in the same small volume of liquid that surrounds them. This liquid would become saturated with colour, tannins and flavours and therefore dissolution of these compounds into the liquid would stop. The process of mixing disturbs the juice and the skins so that juice that is not saturated with these compounds comes into contact with the skins. Therefore, mixing promotes extraction. Leaving the cap of grape skins to float at the top of the liquid also causes the top of the cap to dry out and therefore these grapes do not contribute to the extraction. Mixing also helps to distribute the heat produced during fermentation and is therefore essential for temperature monitoring and control.
Choices regarding cap management have a key influence on the style of the wine. First, there are many different techniques for mixing the skins with the liquid, as outlined below. Second, the winemaker can alter the frequency of the mixing and the duration of the mixing (e.g. pumping over the must three times a day for 15 minutes will extract more than 10 minutes of pumping over once a day). Third, the timing of the mixing within the fermentation can influence what compounds are extracted. For example, more mixing at the start of fermentation with less mixing at the end will extract more colour and less tannin, whereas mixing more at the end of the fermentation will extract a greater amount of tannin.
Temperature also has a role. Warmer fermentations will extract more than cooler fermentations. With temperature-controlled vessels, temperature during different stages of fermentation can be adjusted. Therefore, tannin extraction can be reduced by cooling the wine near the end of the fermentation at the time when tannins are most likely to be extracted.
Punching down
– A plunger is used to submerge the cap of grape skins in the liquid. This can either be carried out by hand or by a mechanised plunger. Carrying out this procedure by hand is labour intensive (with the expense that this entails) and is therefore best suited to low-volume production of premium wines. It is also only physically possible to punch down the cap and ensure adequate mixing of the skins in relatively small, open top vessels. It is a gentle process and used on several grape varieties. It is often referred to by its French name ‘pigeage’.
Pumping over
– In this system, juice/wine is taken from near the bottom of the vessel and sprayed over the cap of skins. Usually around one-third to one-half of the liquid in the vessel is pumped and sprayed over. The juice extracts colour, tannins and flavours from the cap of skins as it passes through. Because this technique sprays the liquid over the cap, rather than breaking up the cap, the extraction is very gentle and usually punching down or rack and return is also required to extract enough colour, flavour and tannin. This technique can be carried out aerobically, for example by splashing the wine into a new container and then pumping it from there up over the cap of skins. This exposes the must to oxygen, which can be beneficial for yeast health and avoidance of reductive off-flavours such as rotten eggs. It is also possible to carry out pumping over anaerobically in closed vessels by attaching the hose to a tap at the top of the vessel or simply by keeping the hose close to the cap of skins in an open vessel. It is commonly used on all black varieties, for wines of all price points and qualities and is suitable for use on large vessels. Modern wineries have pumps and hoses installed at each tank, and pump-overs can be pre-programmed to occur at certain times and for certain durations, reducing the need for labour. It is often referred to by its French name ‘remontage’.
Rack and return
– This is similar to pumping over; however, the juice is pumped from one vessel into another vessel. As the juice is being pumped out of the vessel, the cap of skins falls down the vessel. The juice is then pumped from the new vessel in through the top of the original vessel and is sprayed over the skins. This breaks up the cap and mixes the juice and skins thoroughly. It is more extractive than pumping over or punching down. For this reason, rack and return may be used only 1–3 times during the fermentation, alongside punching down and pumping over. It is most commonly used for red wines where medium to high levels of flavour, colour and tannin are desired (e.g. Cabernet Sauvignon- or Syrah-based wines). Rack and return cannot be fully automated and requires labour to set up and monitor the process. It also requires a clean vessel to be available, which can be an issue in wineries that are operating at peak capacity. Rack and return is often referred to by its French name ‘delestage’.
Ganimede® tanks
– These specialised tanks bubble CO2 up through the must/wine. Pressure builds up under the cap, until finally the cap bursts. This technique breaks up the cap quickly and therefore, like rack and return, it is relatively extractive and suited to producing wines with medium to high levels of colour, tannins and flavour intensity, such as Cabernet Sauvignon- or Syrah-based wines. This is a relatively new technique, but one that is becoming increasingly common because it can be fully automated and is therefore less labour intensive than rack and return. However, these specialised tanks are slightly more expensive than standard stainless steel tanks. Oxygen can be used instead of CO2 if the winemaker wants or needs to exposure the must/wine to oxygen during the fermentation.
Rotary fermenters
– Rotary fermenters are horizontal, closed, stainless steel tanks. The whole tank rotates and internal blades break up the cap and ensure adequate mixing. The horizontal orientation of the tank increases the surface area between the grape skins and the juice. Rotary fermenters are very effective at extracting and are therefore best suited to the production of wines with medium to high levels of colour, tannin and flavour intensity, such as Cabernet Sauvignon- or Syrah-based wines. The tank can be programmed to rotate at certain times and for a certain amount of time, so labour requirements are low. This type of fermenter is commonly used for high-volume, inexpensive or mid-priced wines that are acceptable or good in quality. They are very effective at extracting, and techniques that are gentler or allow a bit more precision are usually preferred for very good to outstanding, premium-priced wines. These tanks are relatively expensive compared to standard stainless steel tanks and therefore large volumes of wine need to be fermented in them to make them cost effective.
What other maceration options are there during fermentation?
Must concentration
– Although not strictly a way of increasing extraction, the levels of colour, flavours and tannins of the wine can be increased by drawing off some of the juice just after crushing and before the start of the ferment, concentrating the remaining must. This lowers the volume of red wine that will be made from a set weight of grapes, which has implications for the price of the wine; however, the juice that is removed is typically light in colour, flavour and tannin and can be used to make rosé. It is often referred to by the French term ‘saignée’.
Co-fermentation
– This is the process of fermenting different grape varieties together in the same vessel. The term most commonly refers to the practice of fermenting a small proportion of white grapes (typically up to 5 per cent) within a red wine fermentation. The latter technique is reported to take advantage of some of the phenolic compounds found in white grape varieties that can increase colour intensity and stability through binding with anthocyanins, and therefore may result in higher quality. The white grapes can also contribute aroma compounds (e.g. the terpenes in Viognier give floral and fruity characteristics). However, research into this area shows mixed results, and adding too much of the white grape variety can lead to dilution, and hence lower colour intensity. This technique originated in the Rhone Valley, with the Côte-Rôtie appellation particularly famous for the co-fermentation of Syrah and Viognier. It has since been imitated in many other regions and countries both with Syrah/Shiraz and Viognier, but also a range of other black and white grape combinations. (However, in some cases these are just blends of red and white wines, to benefit from the fruity or floral notes of the white variety, and so the influence on colour stability is diminished.) This technique does not incur any particular
Explain whole berry/bunch fermentations?
It is also possible to use uncrushed fruit in fermentation. Winemakers can either choose to use whole bunches of grapes or whole destemmed grapes, and to use either entirely uncrushed fruit or just a small proportion in a crushed fruit fermentation. If whole bunches are used, the grapes must have been hand harvested.
If whole bunches of grapes are used it is very important that the stems of the bunches are fully ripe. Stems can add flavours that are sometimes described as ‘spicy’ or ‘herbal’ and can also add some tannins. However, unripe stems can add unpleasant green flavours and bitter tannins. Winemakers can also choose to add stems (left over from the destemming process) to crushed fruit fermentations to provide some tannins and spicy flavours. It is not common to add stems when fermenting grape varieties with naturally high tannins, such as Cabernet Sauvignon.
The objective of whole berry/bunch fermentations is to create an oxygen free environment for the uncrushed fruit. This lack of oxygen has several outcomes. The grapes change from aerobic respiration to anaerobic metabolism. In the anaerobic process, some of the sugar in the grapes is converted to alcohol. This occurs without the involvement of any yeast and is referred to as intracellular fermentation. Malic acid within the grape is also broken down to create ethanol. This can reduce the malic acid levels by up to 50 per cent, lowering the total acidity and raising the pH of the must/wine. Glycerol levels increase, which can add texture, and a range of distinctive aromas is created inside the grape, commonly including kirsch, banana, bubble gum and cinnamon.
These techniques themselves do not have a significant impact on costs, and it is more likely that other parts of the production process (e.g. hand-harvesting, sorting of fruit, use of oak if desired) will have greater impact on the price of these wines.
Explain carbonic maceration?
This involves placing only whole, uncrushed bunches into vessels that are then filled with CO2 to remove all the oxygen. This causes the intracellular fermentation to start. Once the level of alcohol in the grape reaches 2 per cent, the grape skins start to split and the grapes release their juice. The juice is generally drained and the grapes are pressed at this stage to separate the juice from the skins. The free run juice and press juice are typically blended. Yeast then complete the fermentation off the skins.
Importantly, this method extracts colour from the grapes, but little tannin (the alcohol is only around 2 per cent when the grapes are pressed, and tannin is most easily extracted in the presence of alcohol). The resulting wines typically have low tannins with distinctive notes of kirsch, banana, bubble gum and cinnamon-like spice from intracellular fermentation, alongside the fruit notes from the grape variety. The flavours of oak are usually not a desirable addition to the fruity, candy-like flavours of these wines, keeping production costs relatively low.
These wines are defined by their fruity, low tannin profile and are best consumed within a year after harvest. The flavours created are distinct, but not especially complex. However, in some cases they may improve grapes that have been grown at high yields or that have not reached full ripeness. This technique therefore tends to be used for acceptable or good, inexpensive and mid- priced wines. Beaujolais is a region famous for using this technique on some of its wines, particularly Beaujolais Nouveau.
Explain semi-carbonic maceration?
This is a similar but slightly different technique that does not involve filling the vessel with CO2.
The vessel is filled with whole bunches. The grapes at the bottom of the vessel are crushed under the weight of the grapes above and some juice is released. Ambient yeast start to ferment the juice (cultured yeast can also be added). This fermentation produces CO2, which fills the vessel and the remaining intact grapes undergo carbonic maceration. As the intact grapes begin to split and release their juice, the grapes are pressed and yeast complete the fermentation off the skins.
If the winemaker wants to make a wine with slightly more concentration, body and tannin, and hence a longer ageing capacity, the alcoholic fermentation may continue on the skins and involve some punching down or pumping over. An ever-decreasing amount of carbonic maceration takes place until all the grapes are broken up. The alcoholic fermentation may be followed by a post-fermentation maceration and/or maturation in oak to add complexity (with the cost implications associated with these techniques). This approach can lead to a better integration of the aromas from intracellular fermentation with aromas from the grape variety. It results in wines with more fruitiness and a softer mouthfeel than crushed fruit fermentations, and is a technique sometimes used when making fruity styles of Pinot Noir, Malbec, Tempranillo, Gamay and Carignan, among other grape varieties.
Explain whole berries/bunches with crushed fruit?
A further variation is to mix whole berries/bunches with crushed grapes in the fermenting vessel at the start of the fermentation. If whole bunches are used, care is needed that the stems are ripe as they will be macerating in the juice/wine during the fermentation.
Although the whole berries/bunches in the vessel are not blanketed in CO2, they are largely submerged by the crushed grapes and kept away from oxygen, therefore intracellular
fermentation takes place. More ‘carbonic’ characteristics can be achieved by raising the percentage of whole berries/bunches that are present at the start of the fermentation. The whole berries/bunches are progressively crushed during the fermentation as the cap is regularly punched down. Similar to semi-carbonic maceration, a period of post-fermentation maceration and/or oak maturation may follow. It is difficult to define the effect of whole berries/bunches with crushed fruit due to the many ways that winemakers use this technique; however, it is generally thought to give a smoother texture and more vibrant and fresh primary aromas (than crushed fruit fermentations). It is used on a wide range of grape varieties and wines of different qualities and prices.
Explain fermentation temperatures and vessels for red wines?
Red wines are usually fermented at warmer temperatures than white wines because higher temperatures help to promote extraction.
However, warm temperatures can cause volatile, fruity aromas to evaporate, so, depending on the style of wine, a balance needs to be struck. Winemakers wanting to produce fruity, low tannin wines will typically ferment at relatively cool temperatures (e.g. 20°C / 68°F). Winemakers wanting greater extraction to produce wines with the concentration and tannin structure to age, may ferment at slightly warmer temperatures (e.g. 30°C / 86°F). The temperature can be monitored and controlled throughout the fermentation to increase or reduce the extraction of certain compounds (e.g. cooling the ferment near the end to avoid excessive tannin extraction) and also to generally promote a healthy ferment to dryness.
Red wines may be fermented in stainless steel, concrete or wooden vessels. These can be open at the top, which is needed for extraction techniques such as punching down, or closed vessels. If oak is used for fermentation, it is generally in the form of a large vat; however, small oak barrels (e.g. 225–500 l) are sometimes used. The barrels are kept on their side, with one of the heads removed to form a very small, open top fermenter. Managing fermentations in these vessels is extremely labour intensive, and therefore typically limited to premium- and super-premium priced wines. It is thought that fermentation in oak gives a rounder mouthfeel to the wine and leads to better integration of oak compounds during maturation. Concrete and stainless steel help to retain fruit flavours.
What is post-fermentation maceration?
Some winemakers may choose to leave the wine macerating on the grape skins for a period of time (from a few days to a few weeks) after fermentation. This practice is thought to further extract tannins and encourage the polymerisation of tannins, with the aim of improving tannin structure and texture and the wine’s ageing potential. These effects mean that it is generally conducted on premium and super-premium, very good and outstanding wines that are intended for ageing. Post-fermentation maceration also takes up tank space and time, so it is often not possible or desirable from a logistical point of view in the production of high-volume, inexpensive wines.
Explain the pressing of red wine?
Pressing separates the wine from the skins and therefore takes place when no more extraction is desired. For options about the types of press used for red wine, as for white. Red wine is usually better protected against the effects of oxidation than white wine, so techniques such as flushing the machines with inert gas are less widely practiced. The free run wine will be drained from the fermentation vessel, and the mass of grape skins then removed for pressing. Press wine may be mixed with free run wine as a blending component to add extra colour, flavour and tannins. Press wine that is not wanted may be sold to another winery or for distillation.
The timing of pressing is relatively variable in red wines (compared to white wines) and depends on the style of wine being produced. For wines that have been made by carbonic maceration, pressing may occur when the fermenting must reaches 2% abv to produce a wine with medium levels of colour and fruity flavours but low tannins. At the opposite end, some red wines will be pressed after a period of post-fermentation maceration to maximise the tannin structure of the wines. The winemaker also has the option to press straight after alcoholic fermentation is complete (the wine is dry), or press just before the end of alcoholic fermentation, usually with the intention that the wine will finish fermenting in barrels. This latter practice is thought to lead to a better integration of oak flavours and rounder mouthfeel.
Explain malolactic conversion for red wines?
Malolactic conversion is routinely carried out for red wines. However, the winemaker can choose the vessel in which malolactic conversion occurs; it is felt that malolactic conversion in oak barrels can lead to a better integration of oak characteristics during maturation. The winemaker can also decide whether to encourage malolactic conversion to occur during alcoholic fermentation, or whether it will take place after fermentation has ended.
Malolactic conversion will decrease the acidity and increase the pH of the wine. It is possible to adjust the acidity of the wine as necessary (this adjustment can also be made at the must stage). It is also possible for winemakers to reduce the alcohol of the wine at this stage.
Explain maturation in wood vessels for red wines?
As with white wines, maturation in oak vessels can have a significant impact on the style of a red wine. However, maturation in oak is generally much more common for red wines than white wines, particularly for wines that are mid-priced or more expensive.
Inexpensive red wines are likely to be released soon after fermentation for cost and logistical reasons, and therefore do not generally undergo maturation in barrel. The winemaker may choose to obtain the spicy flavours of wood from oak alternatives such as staves, which can be inserted into a stainless steel tank or concrete vat and can provide oak flavours cheaply and quickly.
The majority of mid-market, premium and super-premium red wines will be matured in oak vessels for at least a few months. A proportion of new oak may be used if the winemaker feels the flavours of oak (vanilla, cloves, etc.) would enhance the complexity of the wine. Furthermore, the gentle oxidation that occurs, particularly in small oak vessels such as barrels, helps to soften tannins and can lead to the development of tertiary aromas and flavours that can enhance complexity and quality. (These tertiary characteristics will develop over time and therefore, in standard cool cellar conditions, are more likely to be present in a wine that has been aged for a couple of years, rather than a few months.)
It is possible to find examples of mid-market and premium red wines that have not been matured in oak or have only undergone a minimal period of ageing in old oak; usually in cases where the winemaker wants the focus to be on the primary aromas and flavours of wines. Examples include some Loire Valley Cabernet Francs, Spanish Mencias and Argentine Malbecs, among others. Do note that these are exceptions, and the majority of wines from these regions and grape varieties will be matured in oak. However, there has been a trend in many wine regions over the last few years to use less new oak, and hence gain more subtle oak flavours alongside the primary fruit.
Explain lees ageing for red wines?
Lees ageing can help soften tannins in red wines. However, a possible disadvantage is reduced colour intensity. Racking can be used to separate the wine from the lees, and therefore control the amount of lees present in the vessel throughout the maturation process. It is not typical to keep gross lees nor to stir the lees when making red wines.
