There are several types of vessels in which the fermentation process can take place. Anything from a small plastic bucket in someones home, to old oak barrels or massive temperature controlled stainless steel tanks. It’s all being done. Here is some more wine-speak around turning juice into wine. (Click here to view part one)

Stainless steel tanks

Most modern wines are today fermented in stainless steel tanks. They certainly have their advantages. It is easier for the winemaker to control the temperature during the process and at the end of it they are easier to clean. It is also a worthwhile investment for those wineries who are doing the volume. Although a large upfront cost, they eliminate the need to replace expensive oak barrels or wooden vessels, which only have a certain life span. Stainless steel tanks can be used over and over again and they provide consistent results.

Wooden vessels & cement vats

Wooden fermentation vessels are still widely used in Europe, and although they don’t have the same longevity as steel tanks, they can be used multiple times depending on the quality. Winemakers prefer old oak for fermentation as it offers natural stabilisation and clarification without adding the overpowering flavours that new oak would bring. Lined cement vats can also be used, some producers believing they provide better aeration than steel tanks.

Maceration & carbonic maceration

Although not a type of (or a tool for) fermentation, this is a very important process for red wine making. Maceration takes place during fermentation. It is the extraction of tannins, as well as the flavour and colouring elements of the solids (grape skins, seeds and stem fragments), into the juice, and depending on the winemakers time constraints it can continue on after fermentation has finished. It is argued by some winemakers that maceration is better done in wooden or cement vats. Carbonic maceration involves maceration without crushing the grape skins. More on that here.

Malolactic fermentation (MLF)

MLF is not technically a process of fermentation but a process of conversion. That is the conversion of the acidic malic acid into the less acidic lactic acid. This is why sometimes an unoaked Chardonnay may still have vanilla/buttery aromas and a creamy texture on the palate. Cooler climate red wines can also benefit from MLF, helping to soften that high natural acidity and bring extra flavour complexities. Ultimately, it all depends on the style the winemaker is trying to achieve, however, care must be taken on to over-do MLF as this can jeopardise the overall balance.

Second fermentation

This is essential for sparkling wines. It can either take place in a pressurised tank or in bottle. This article helps explain further.

Pictured: Basket press at Langmeil. Click here to view part one.

With early harvests across Europe, it’s around about now that winemakers will be commencing or monitoring the fermentation process – put simply, that all important conversion of sugar to alcohol.

Open up a fermentation tank and it will look like a boiling pot of grape juice. This is the other by-product of the fermentation process, carbon dioxide, escaping into the open air. At this stage the winemaker will be keeping a close eye on what’s going on inside the vessel.

In some high-tech wineries it is possible to weigh the vessel at different times to check how much Co2 has been lost, and thus work out how much sugar should remain. The most common technique used is the measurement of density. Hydrometers can be calibrated to determine density and provide a reading of the sugar’s percentage in weight, however, this becomes less accurate the more alcohol is produced because alcohol is less dense than water.

Knowing when fermentation has finished is crucial. If fermentable sugar remains, the wine becomes susceptible to bacterial attack and may need to be treated, so many wineries now take measurements using paper strips or hand-held density meters. For producers of bulk wine, devices can be fitted within the vessel and the beginning and end of the process can be decided by a computer. The result is consistency, even if one might say these wines are characterless and one dimensional, consistency is what their target market demands.

Red wine is usually fermented within four to seven days, white wine takes longer as it is fermented at a lower temperature, often a few weeks. The temperature, the type of yeast, the aeration of the must will all have an impact on how long the process takes. Over time, experienced winemakers will find a formula that suits their style. For example, they might rely on a certain yeast for a particular wine and based on previous experience they will have a good idea of how long the fermentation will last. For the big producers looking for a quick turnover, the speed of the process is often hastened to free up vessels for more juice.

Click here to view part two.

Everyone needs a human touch now and again, as Bruce Springsteen well knows. It’s the same with grapes. They need to be nurtured, protected, cared for, loved and caressed (OK, maybe caressed is going a little too far, but you get my point).

In the vineyard it is man who decides on location and aspect to the sun. It is man who manages irrigation and prunes vines to enhance concentration. And it is man who decides when it’s the right time to pick the grapes. Consistently tasting the berries and testing the sugar levels, the farmer decides on the exact day, and right time of the day, to start harvesting. The fun begins after harvest.

After all the time and work dedicated to growing the grapes, they are hand-picked or machined harvested before being placed into baskets and brought to the winery. For whites wines, white or pink grapes are used (the white Pinot Grigio, for example, is made from a pink grape of the same name). Most white wines don’t endure prolonged contact with the skins, so the grapes are crushed with the skin and juice being separated.

The juice goes into a settling tank, where the the undesirable solids sink to the bottom. When the winemaker is happy with acidity and sugar levels, the juice is ready for fermentation. This is the stage that the natural sugars in the fruit juice are converted to alcohol.

Typically white wine is fermented between 18-20 degrees centigrade in the Old World (Europe), and 12-17 degrees in New World countries (the Americas, South Africa, Australia, etc.) where there is a greater determination for fruit. Fermentation can last for anything from a few days to a few weeks depending largely on the temperature.

Red wine is fermented at higher temperatures (typically 25-30 degrees C), and as a result tends to occur more rapidly (usually 3-7 days). Red wine is made exclusively from red or black grapes as its the skins that give the wine its rich colour. Depending on the grape and the type of wine desired by the winemaker, the skins are left in contact with the juice during the fermentation process. More contact means more colour and richness, but can also mean more astringency (you know, the harsh, puckering taste you might experience in cheap or wines that need ageing?), so the balance is essential to getting the structure of the wine right.

After fermentation, both red and white wines are clarified to remove any remaining skins or other solids, and left to rest in steel or oak tanks. Much wine these days (in the particular the volume supermarket stuff) is bottled very soon after to provide quick sale and cash-flow for the wine-maker. Other wine is held back for ageing to develop more complex flavours. This is particularly true for wines aged in oak.

Some grapes suit ageing better than others. Most reds will benefit from some, and in the whites the likes of Chardonnay and Riesling are quite capable of lengthy ageing processes, particularly in the bottle.

So, the year of vintage printed on the bottle now gives you an indication of the type of wine you should expect to taste. The vintage is the year the grapes were harvested and the wine made. So a 2008 Sauvignon Blanc should be crisp, clean and straightforward, with lots of fruit to the fore, whereas a 1998 Chablis (made from Chardonnay) is going to be more complex, less fruity but with other complexities like yeast, or spice, or even a creaminess to the texture.

Happy, and more knowledgeable, wine-drinking this weekend.