Fermentation is one of the most important parts of winemaking. To help with the fermentation process, there are several types of vessels that can be used. The three most popular types are stainless steel tanks, oak barrels and clay tanks.
Steel tanks and oak barrels are found in most wineries around the world. The use of clay tanks started making an appearance in more cellars in recent years, however, the practice of using concrete or clay vessels dates back to ancient civilizations – including Greeks, Romans, Egyptians, Canaanites.
At Aurora Cellars, we have used steel tanks and oak barrels but recently we purchased and started using a clay “Amphorae”.
Why Use Concrete Vessels?
VinePair explains that over time, winemakers were starting to think stainless steel tanks would produce sharp, linear wines that wouldn’t have the chance to breathe. This caused winemakers to start considering clay tanks. A concrete or clay tank is a heavy, thick-walled vessel that comes in many shapes and sizes, from standard ovals to squares, pyramids, and even eggs.
Due to the porous nature of the vessel, Head Winemaker Drew Perry explains how this allows the wine to develop slower than in oak, but faster than it would in steel, because it allows the tank to exchange gas and oxygen at a far lower rate. According to experts, the thousands of tiny pockets in the clay trap air and allow the wine limited contact with oxygen.
Our vessel has a gas release that allows gas to escape through the water while preventing anything else from getting into the tank. Wine Folly explains semi-porous materials, such as concrete, ceramic, terracotta, and permeable plastic, are often used to make the egg-shaped fermenters. These types of building materials offer a way to expose the wine to small levels of aeration.
When wine is exposed to low levels of oxygen, it begins to age gradually, developing more flavor, softening tannins, and improving mouthfeel. Wines that are aged in the inert and airless environment of stainless steel take much longer to achieve similar levels of aging.
Unlike stainless steel tanks and oak barrels, clay tanks don’t impart any additional flavor on the wine. Winemakers are able to maintain freshness and purity of a grape’s character. “Overall the difference wouldn’t be in flavor, as much as it would be in palate development,” says Perry. Experts explain wines created in concrete tanks tend to be bright and fruit-forward, with excellent texture and minerality.
What Varieties Are Best For the Vessel?
According to wine-searcher.com, clay eggs are generally best suited for wine styles that will benefit from micro-oxygenation – such as red wine. Micro-oxygenation is “the process of deliberately introducing minute, measured amounts of oxygen into wines, with the aim of bringing about desirable changes in color, aroma and texture.” Clay eggs are designed to give the body of an oaked wine while still clearly expressing fruit characteristics and terroir.
These vessels are most often associated with white wine. While this might be the case, winemakers believe red wine can be fermented in a concrete vessel because of the design of it.
The clay vessel is new to the program and therefore we are still learning what varieties do well in it. Perry believes dry white wines that would benefit from aging on lees would be excellent in clay vessels as well as fruit forward reds that have a need for extended aging.
Currently, the 2022 Pinot Noir is aging in the vessel. Starting next season, Perry explains our team will likely expand into both fermentation and storing in this type of vessel. “It is our first time using this style of vessel, so we wanted to introduce one or two varieties at a time.”
How Does A Concrete Vessel Work?
After reading this, you might be wondering, “How does the fermentation process happen inside a concrete vessel?”
Since there are no corners on these vessels, the wine is able to freely circulate naturally during the fermentation process. The vessel’s shape also forces more of the cap that forms on the wine to remain submerged, which helps reduce the need for a “punch down.” Winemakers suggest the thick concrete or clay walls draw heat from the fermentation and insulate it.
Clay eggs can be used both as fermenters as well as a vessel for wine maturation. The egg shape is thought to be desirable for gently and constantly circulating lees as the wine matures after malolactic fermentation. The properties of these vessels also mean the winemaker doesn’t need to intervene as much.
(An infographic showing what is happening with the yeast and heat in the wine while inside the concrete egg. Graphic courtesy of Wine Folly.)
Wine Folly explains that due to the vessel’s shape, smooth internal surface and lack of corners, a natural current or “vortex” happens within the fermenter. As active yeast ferments wine, it becomes lighter and rises to the top of the fermenter. Cooler wine then sinks to the bottom, resulting in the formation of a continuous convection current. The “vortex” current causes lees to remain in suspension throughout fermentation, which helps build texture and flavor in wines.
We are excited about the addition of the clay vessels within our winemaking program and look forward to sharing these wines with our patrons. We will be watching the development of these wines overtime to see how they age in contrast to their counterparts aged in stainless steel or oak barrels.
