In theory, and only in theory, almost any vessel can be used for fermentation. So much so that many of us made our first wines in containers designed for anything but winemaking, and many artisanal and home winemakers use such containers every year to make their wine.
Throughout history, a wide range of materials have been used for these vessels: first clay jars, then wooden vessels, later cement, and finally, in recent decades, metal vessels, especially stainless steel.
Today there is a revival in the use of concrete or cement vessels, both in the traditional cube or rectangular shape and in so-called eggs, which are essentially egg-shaped vessels.
In ancient times, the type and material of the vessel used to ferment and store wine were often tied to the resources available where the wine was made. In forested areas, wood was commonly used to make vessels, since it was readily available.
In areas where wood was perhaps less abundant but pottery was possible, clay was used to make vessels to hold the wine.
In other places, where both wood and clay were scarce, people always found ways to make vessels from whatever materials they could find, such as treated animal hides and other items.
What mattered was making wine and having somewhere to keep it. Below we take a brief look at each of these materials, with some of their advantages and disadvantages.
Clay jars and vessels
These are no longer widely used commercially, since they have the disadvantage of being very fragile and therefore hard to handle. In addition, the tartrate salts naturally present in wine stick to the walls and are very hard to remove. That same rough surface makes these vessels very hard to clean, and their pores harbor all kinds of microorganisms, which may be beneficial or harmful.
When the microorganisms are spoilage bacteria or yeasts, they are very hard to get rid of, and every time the must comes into contact with the vessel it becomes contaminated. This does not necessarily spoil the wine right away, but it can trigger problems later. By contrast, in organic or biodynamic wines, the presence of populations of microorganisms that benefit the wine can be a key factor in the quality of the finished wine.
Clay vessels can also give the wine unpleasant flavors and may greatly reduce its polyphenol content, both anthocyanins and tannins, resulting in thinner wines.
Wooden vessels
These are used commercially and come in various sizes and types of wood, with various treatments. They are used either for fermentation or for aging and maturing red wines.
Their disadvantages are that they are hard to clean and very susceptible to rot and other microbial spoilage. To ensure consistent quality year after year with these vessels, the winery needs a cooper on staff to give them the maintenance they require when they are not holding wine.
One example of wooden vessels used for fermentation can be seen at the Mondavi winery in California, USA, which has (or at least had the last time I was there) a fermentation hall in which every tank is made of fine wood and used exclusively for fermentation. For the other 9 to 11 months of the year, the tanks must be kept under strict hygiene control and rigorous maintenance to prevent the wood from drying out and to stop wood-borne microorganisms from growing that could later spoil the wine.
Trained staff are responsible for keeping the tanks hydrated enough during that time so that they don’t leak when they are used, yet dry enough that no fungus or other microorganism can grow on or in the wood.
Cement vessels
Cement vessels have long been used for fermentation for a variety of reasons, both economic and technical. Their disadvantage is that they are highly reactive with the acids in wine, which gives it unpleasant flavors.
To counter this problem, their inner surface must be protected with epoxy or other linings that prevent the wine from coming into direct contact with the cement. In the past, the wine’s own tartrate salts, deposited on the cement, coated the inside of the tank, but keeping them in place meant the tanks had to be cleaned with extreme care. This, together with the nature of tartrate salts, encouraged the growth of all kinds of spoilage microorganisms in the wine.
The way these tanks are built and the material they are made of give them thermal properties that cannot be achieved with stainless steel tanks: they are extremely well insulated from their surroundings, which can be an advantage in some circumstances and a drawback in others.
During alcoholic fermentation, rigorous temperature control is very important, and because concrete insulates so well, this control has to be carried out from inside the tank with very good equipment capable of removing heat quickly. This is achieved with cooling coils or heat-exchange plates inside the tank. This “disadvantage” of insulation during fermentation can be an advantage when carrying out late malolactic fermentations, which require more warmth.
Some wineries are taking advantage of these thermal properties at critical points in the process, such as malolactic fermentation or cold stabilization.
Stainless steel vessels
Of all the metals known to us, stainless steel is one of the few that can be used for fermenting wine at a reasonable cost. This is because it has very low reactivity, does not add foreign elements to the wine and conducts heat well.
It requires the highest investment of all the vessels discussed here. These vessels are generally made of austenitic stainless steel alloys, the most common being AISI 304 and AISI 316. The metal’s workability during manufacturing, the very low mass-to-volume ratio of the vessels and its inertness in contact with must or wine have made it one of the most widely used materials in winemaking over the last 30 years.