Jane Masters MW is Opimian’s Master of Wine
Tanks come in all shapes and sizes. They can be made from concrete, wood, epoxy-lined steel, stainless steel or plastic. The style and flavour of a wine is influenced by the materials from which the tanks are made; some such as wood impart flavour; others are more neutral, yet still have an effect.
When stainless steel tanks were first introduced into wineries in the 1960s and 70s, they were revolutionary, becoming the “must-have” tool for winemakers. Easy to clean and with simple temperature control, they eliminated many problems, like off-odours from undesirable microbial activity and oxidation. Concrete tanks and wooden vats were replaced with banks of shiny, new stainless ones in many wineries that could afford to do so. But in recent years, concrete has been making a comeback. Hip winemakers rave about it and I have seen entire new wineries based on concrete tanks in regions as diverse as Argentina, Bordeaux and Rioja.
The size, dimensions and shape of a tank, as well as the material from which it is made, have an impact on the wines produced. Temperature affects the growth and metabolism of yeast and the rate of fermentation. The alcoholic fermentation itself creates heat; as yeasts consume sugar and convert it into alcohol, the temperature of the fermenting must rises. If the temperature is too cold, yeasts are sluggish; if too hot, they die off. Temperatures between 15º and 30ºC affect which aromatic compounds are produced and in what quantities and ratios. The thermal properties of a tank have a bearing on whether heat is dissipated or retained. The larger the tank, the lower the ratio of surface area to the volume of liquid contained in it, meaning that heat is less easily dissipated through the tank’s walls. Stainless steel tanks gave winemakers greater control in maintaining a desired temperature—particularly important for producing fresh white and rosé wines for which lower fermentation temperatures give better results.
Most tanks are cylindrical, conical, or in the case of traditional concrete tanks, cuboid. As red wines ferment in the presence of grape skins, carbon dioxide produced by the yeast bubbles up to through the tank to escape from the top, carrying with it the skins which form the “cap”. The skins, containing colour and tannins, float on the top of the fermenting juice. Winemakers use various techniques, like pump overs and punching down, to extract the phenolic compounds. A tall, thin tank has a much thicker cap than a wider tank, so the same size tank makes extraction different.
Concrete is a thermal insulator. It is also porous, albeit on a microscopic scale, allowing a small ingress of air for the wines to mature and develop a smooth, round mouthfeel similar to that of oak, but without the oak flavour. Before the 1960s, concrete tanks were part of the structure of the winery building, often built with brass valves (which could cause high levels of copper in wine). These were difficult to clean and maintain, and over the years they built up thick layers of tartrate crystals harbouring all sorts of microbes.
Nowadays concrete tanks can be produced in different shapes, small sizes and a variety of colours. It is increasingly common to see “concrete eggs”. The idea was hatched by Rhône winemaker Michel Chapoutier in the early 2000s, who developed them with French tank manufacturer Nomblot. The ovoid shape creates a convection current or vortex inside the tank, keeping the wine circulating and resulting in a similar effect to lees stirring so that the wines develop more complex flavours and mouthfeel. The shape is so popular that oak and breathable plastic eggs now also exist. Wines produced in concrete tend to be pure mineral wines with supple tannins and texture. That is not to say better necessarily, just different. I am all for extending winemakers’ palettes with a diversity of interesting flavours and styles.