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A Technical Guide for Wine Producers
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WHAT'S UP IN THE VINEYARD AND CELLAR
Automation of the red wine fermentation process
Skin contact before and during the alcoholic fermentation of red wine is a given except when using thermovinification, in which case the heat benefits extraction from the skins. Traditionally the mixing of the juice and skins in red wine vinification has always required a considerable amount of manual labour and late working hours, whether this took place by means of racking or punching down. Cellars therefore had no option but to consider automatic methods.
Various kinds of new equipment have been developed to facilitate the red wine fermentation process. This includes inter alia the stacking of tanks, the programming of racking or juice/skin mixing, the use of tanks with sloping bottoms that facilitate cleaning or the removal of grapeseeds, or tanks designed for the installation of wooden staves. The most revolutionary development is probably the use of compressed air to favour the mixing of the juice/skins. Although this principle was first used in the USA in 1985, its popularity dates from 2001.
To impart a French connotation to the technique, it is referred to as pneumatage and it can obviously be seen as a replacement for two other well-known French techniques, namely pigeage (punching down of the skins) or remontage (racking and aeration). The following method was used to develop the technique: a standard steel pipe that reaches below the skins layer, is attached to an air compressor and the pipe is attached to the lid of the tank using a three-piece. The air supply through the pipe may be programmed, and when the air moves through the pipe a huge air bubble is created that rises up towards the surface of the skin crust, which it then breaks up, thereby ensuring that the juice and skins are mixed. The programme can obviously be adjusted to ensure different durations and frequencies of mixing.
The air to be used has to be purified. A standard compressor will have to be equipped with a filter and a piston compressor will have to be fitted with an oil filter. Air is preferable to nitrogen, since air will stabilise the colour and also promote yeast growth due to its high oxygen content.
There are various methods to break the skin crust. More and more fermentation tanks have slanted or cone shaped bottoms. This offers numerous advantages with regard to the cleaning of the tanks, vinification techniques and safety. Lees and grapeseeds settle in a compact substance in such tanks and are easily removed. The removal of the grapeseeds also reduces the so-called green character of red wines. It is easy to clean the bottoms of the tanks without the cellar workers having to enter the tank. Tank suppliers are able to offer different combinations of tank bottoms, pneumatage and stirrers, thereby giving winemakers various options. Labour may be significantly reduced and the resulting grapeseeds are so clean that they are preferred by the suppliers of grapeseed oil. The shape of the tank also plays a very important role in the vinification process. Conical tanks, the base of which is broader than the top, have a thicker skin crust and more contact with the juice. It is also easier to break the skin crust to improve juice/skin mixing. As a result of the smaller height/width ratio of the tank there is less pressure on the bottom of the tank, seeing that high pressure may hamper the activities of the yeasts. Although tanks have traditionally been round because fewer corners facilitate cleaning, they require a lot of space. At present it is possible to produce square tanks, which facilitates stacking, with rounded corners to eliminate the cleaning problems of the past (Falchek, 2007).
This information is also available on www.vwm.online.com.
Reference
Falchek, D. 2007. Automating the Fermentation Process. Vineyard & Winery Management, July/August 2007: 64 - 70.
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