Oenology: the delicate issue of vats in the wine-making process
In the collective imagination, vineyard cellars remain imbued with ancestral traditions. The rows of aged wood barrels give the impression that wine ages slowly in these quintessential containers. In reality, a wine cellar is much more complex, and winemakers use different materials based on the advantages and risks for their product. Laurent Gibon, a Bordeaux-based loss adjuster specialised in oenology, explains the various types of vats.
Choosing materials for vats in a wine cellar
In viticulture, the wine-making process takes place in a wine cellar. Before being racked in barrels, wine is made in vats. Vats serve as a container for the grapes, allowing their juice to transform into wine without altering the taste or chemical composition. Wine is stored in the vat for several months as it undergoes various transformation phases driven by key biological and chemical processes, such as alcoholic and malolactic fermentation.
The vat must be able to handle this fermentation without altering, while regulating temperature differences; that’s why thermoregulated vats are useful. Certain materials are more or less susceptible to temperature variations, meaning choosing a vat is an essential part of producing high-quality wine.
Wood vats, a noble yet demanding choice for the winemaker
Wood vats, also called casks, are the oldest form. Made from the ultimate precious wood, oak cask construction requires significant expertise which contributes to its much higher cost. Right from the beginning of their production, wood casks impart subtle aromas that must be understood. Wood also has significant heat retention that limits temperature variations. What’s more, these beautiful wood casks add to the image of a vineyard as wine tourism continues to grow. However, wood must be thoroughly cleaned between two vinifications to prevent mould and bacteria. Poor maintenance can lead to changes in the aroma.
Casks are best preserved through a process called mechage, where burning sulphur is lowered into them. The cost of these vats is also a major barrier. If they are damaged, repairs are costly and complex.
|Cellar with a wood vat
(taken from SARL MARCUZZO Nicolas)
Concrete vats, a strong ally for vinification
After falling out of style for several years, concrete is making a reappearance in cellars. Concrete vats are less attractive than wood, but they are still used more often and are easier to set up. They can even be made in unique shapes (see photo below of glass-shaped vats). Their natural heat retention and lifespan also give them serious advantages. Contact with wine is regulated with an interior lining which can be made of a specific cement or a food-safe epoxy lining. This lining requires regular maintenance to avoid natural cracks in the concrete that may lead to wine loss if molecules like phthalate leach out of plastic or epoxy linings.
|Cellar with a cellar vat in the shap of glass|
Stainless steel vats, for ease-of-use and limited risks
This material is the one most often used in cellars where vats are infinitely reflected. Stainless steel is food-safe, easy to clean, light and naturally neutral in taste, and doesn’t leach. Vats are designed to be thermoregulated using coils. Stainless steel vats are available in every size. The smaller sizes mean grapes can be vinified by plot. In addition, stainless steel can be stored outside.
|Stainless steel vat|
Stainless steel does have some downsides. It is not inert and is often fragile, particularly when exposed to pressure variations (for example, a closed vent causing it to deform during transfers).
Insurance risks are moderate. Welding defects are rare. Only warping occurs regularly during transfer work. Their large sizes, up to 1000 hL, often make them difficult to set up and move, sometimes requiring roofs to be removed. Loss occurs mainly through hoses, pumps and filters during wine transfers.
One final type of vat exists: polyester vats called garde-vin, usually used in small sizes. The major risk is plastic molecules leaching into wine and changing its flavour.
In summary, the selection criteria do not favour one material over another. The cellar master must make the decision based on the characteristics of the wine they want to obtain, maintenance costs (cleaning water), financing costs and the importance of vat appearance for the cellar’s image.
Laurent GIBON, Environment – Oenology Loss Adjuster