Types of Fermentation Vessels

Stainless steel tanks in French winery

Clay Amphorae

Clay amphorae
Positives: One of the most ancient and natural methods of winemaking. No additional flavours imparted from the clay (inert)

Negatives: Intensive labour, for the staving off oxygen and minimal use of valves and doors. Can decrease the amount of wine that can be produced.
Shape: Egg shaped

The most ancient vessels for fermentation of wine is Clay Pots/Amphorae, used by a vast range of wine lovers in ancient civilisations such as Greece, Rome, and Egypt.

Clay is thick with the ability to naturally insulate during the fermentation process, maintaining a low temperature across a longer period of time. It can take up to 3 times longer than in wooden vessels. It’s porous nature is an added benefit, allowing tiny amounts of oxygen into the wine and evaporating small amounts to increase concentration. By using clay vessels winemakers are able to make wines with deep and rich textures, with bright and fresh elements.

The inert nature of the clay ensures a stable fermentation, with silicon crystals within the clay walls to remove tartrates. But while the stabilization takes care of itself, the sanitisation does not. Clay is very labour intensive, with the pores containing many micro-organisms it must be delicately washed, but hot water cannot be used as the clay would start cracking.

Wood

Wooden vats
Positives: Has a natural insulating property to keep the fermentations warm. Adds unique tannins, creating a different texture with oak-driven flavours. Best for red wines, not white wines.

Negatives: Difficult to clean and maintain due to the porous and textured surface, cannot switch between white and red wines. Furthermore must keep the tank hydrated to prevent it drying out before the next fermentation.
Shape: Cylindrical, some without lids.

Wooden tanks are the best form of wooden vessel for fermentation, coming in both closed or open top varieties. Tall and cylindrical, these large tanks are lined with tall oak staves. This allows for all the desirable elements of the wooden characteristics without the struggle of using small barrels. Lasting decades if looked after well, winemakers often opt for wooden tanks over stainless steel when wishing to impart elements of savoury, spice and elegant tannins. These properties will fade with 2-4 cycles of use but the vessel as a whole can still be used with oak adjunctives.

As with the clay pots, the porous nature of the wood lets oxygen in and evaporates a small part of the wine, increasing concentration. Further similarities can be noted with the sanitisation of the tanks, definitely not easy. Furthermore, the wood must be regularly hydrated to prevent the wood from drying out and causing breakage when next filled.

Oak Barrels
Wooden barrels are found all around the world in most wineries. Yet not primarily used for the fermentation process of winemaking. Not to get mixed up with the aging process (in which oak barrels are primarily used for).

Fermentation does not work as well in oak barrels due to their sealed off structure and small size. For red wines, cap punching is required and unable to be performed with a fixed-lidded barrel. But remove the lid off a barrel and it is rendered useless and difficult to store. It may be used for white wine fermentation but with the use of oak the juice ferments at a higher temperature and needs more regular monitoring.

Stainless Steel Tanks

Stainless steel tanks
Positives: No added tannins or flavour to the wine, kept at the same nature of the winemakers creation. Simpler to manipulate with the temperatures and the technology continues to advance.

Negatives: Does focus on the future and the growing element of technology, not ideal for winemakers taking the natural, no electricity route.
Shape: Various

Bursting onto the scene in the 1950s, stainless steel became the new best thing for winemakers. Reducing cost and labour for every worker.

Extremely customisable, winemakers can opt for a certain shape and style that best fits the fermentation process they wish to follow without compromise. A choice between closed and open top tanks is one of the major decisions. The open-top still has a lid but floats atop the liquid, rising and falling with the amount of juice in the tank. Helpful for cap-punching of red wines.

Being a modern creation the manufacturers have chosen stainless steel due to its chemically inert properties, meaning no oxygen can get in without the winemaker adding it and no alternative aromas or characteristics are imparted on the wine. Full control is given to the winemaker to allow a full expression of the terroir on which the grapes were grown. An added bonus is the ease of sanitization, hosing them down with some water does the trick.

So while it is the most modern, versatile, and controllable vessel currently used there are still many winemakers that prefer the more traditional methods and characteristics that feed off of the oak, clay or concrete. The sterile nature provides a purely blank canvas that can be a positive aspect or negative, depending on the wine being created.

Eggs and Concrete Tanks

Concrete tanks
Positives: Has a mineralistic element and allows for a gradual flow of oxygen due to the porous nature. Furthermore concrete slowly warms and cools during the fermentation process, and doesn’t add any oak elements to the wine.

Negatives: Wine pigment remaining in the tanks, more difficult to switch between white and red wine. Also the potential to crack with large fluctuations in temperature.
Shape: Various

Quite the forgotten option for fermentation is the concrete tanks that dropped off most people’s radars when stainless steel stormed in. Yet it is slowly making a comeback for those winemakers that are highly experienced and wanting to stand apart from the nouveau makers.

Able to be made in almost any shape imaginable, concrete tanks can fit into any winery. A more popular style is the egg shape, which promotes circulatory movement within the vessel to allow natural and gentle mixing throughout fermentation.

As with the clay pots, concrete is a natural insulator, cooling during hot days and warming during the cold nights. Taking away one extra task winemakers have to do, and further ensure a gradual fermentation rate. The inert nature of the concrete also ensure the oxygen can get in without all the oaky undertones. Yet there is still debate over the minerality of the concrete feeding into the wine providing a slightly metallic taste.

The metal compounds must be controlled or countered, hence why only professional winemakers opt for the concrete vessels. And with the inability to move the tanks for sanitisation it must be done in the fermentation room and regularly enough to prevent bacteria in the micropores.

Not an easy vessel to use but more natural than stainless steel and simpler than clay.

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