Attention is returning to wines that are fermented and aged in concrete vessels.
Concrete is a building material very familiar to modern people. While concrete is strongly associated with building exteriors and walls, in winemaking it serves as a material for tanks.
Concrete tanks were used in the past as well. Therefore, concrete is not particularly new to winemaking facilities. However, the first wave of concrete was eventually replaced by stainless steel tanks that appeared later, and concrete disappeared from the scene. Now, it is beginning to attract attention once again.
Why Concrete Now?
In modern winemaking where stainless steel tanks have become the norm, any element that can impart different nuances to wine tends to be valued highly. It is in this context that concrete has begun to attract attention.
Previously, chemical compounds and heavy metals used in concrete formulations often caused leaching problems. This made concrete unsuitable not only for wine production but for food manufacturing in general. However, subsequent technological developments have made it possible to create high-purity formulations without additives. The ability to meet standards suitable for food manufacturing has become one of the catalysts for renewed interest in concrete.
A Tank Material with Unlimited Shape Possibilities
One of the most highly valued characteristics of tank materials is the high degree of freedom in shaping.
Concrete tanks are made using what is called the cast molding method. The process involves pouring a liquid-like substance into molds, then drying and hardening it. Recently, 3D printer-based molding has also been employed, but fundamentally, any shape is possible as long as there is a mold.
Since tanks require hollow interiors, complete monolithic molding is often not possible. However, joints between parts can be kept to an absolute minimum. Additionally, these joint sections can also be connected using concrete, which is a characteristic that differs from stainless steel or wooden vessels.
Large-capacity tanks tend to maintain the traditional rectangular shape. However, smaller-capacity tanks are being made in unique shapes unprecedented in the past, such as pyramid-like quadrilateral pyramids and ball-like spheres.
The shapes of concrete tanks may sometimes be distinctive features expected to serve as winery icons. On the other hand, they are often designed with consideration for the convection of liquids contained within. The representative example of such shapes is the egg-shaped tank, called the concrete egg.
Four Characteristics Expected from Concrete
Concrete eggs are primarily expected to deliver four characteristics.
The first is temperature stability of the wine contained within. This stems from characteristics inherent to concrete itself.
The second is convection properties. This is thought to be brought about mainly by tank shapes made possible by using concrete as the material.
The third is oxygen supply.
The fourth is neutrality—not adding flavors or aromas to the wine.
The third and fourth characteristics, like the first, can be said to be features based on the material properties of concrete itself.
Does Wine Temperature Really Stabilize?
Temperature stability is often cited as a characteristic of concrete tanks. This feature is primarily discussed in comparison with stainless steel tanks.
Stainless steel tanks are vessels that are very sensitive to ambient temperature around the tank. If a tank were placed in an environment with an external temperature of 2°C, the temperature of wine inside the tank would easily drop to nearly the same level. This is due to the high thermal conductivity of stainless steel. It is precisely because of this property that temperature management of tanks becomes possible by wrapping cooling jackets around the tank.
Concrete tanks, on the other hand, are insensitive to temperature changes. This is because concrete as a material has a large heat capacity.
Heat capacity, simply put, is the difficulty of a material to warm up. Materials with large heat capacity can store large amounts of heat (thermal storage capacity), so the material itself does not warm up with just a little heat. Conversely, once warmed up, it takes time to cool down.
Imagine asphalt in summer. Even under blazing sun, it doesn't warm up much from morning until around midday. However, once it becomes completely heated in the afternoon, it remains warm even at night after the sun sets.
These characteristics are considered suitable for wine containers.
Wine tanks are never placed under direct blazing sunlight. Therefore, the temperature of concrete used as tank material stabilizes at a temperature close to the room temperature of its location. The thermal storage capacity of concrete still has plenty of margin. In this state, even if external temperatures fluctuate somewhat, the concrete is neither warmed nor cooled, and such temperature changes hardly reach the interior of the tank. In other words, wine temperature is maintained constantly.
Most Concrete Tanks Are Equipped with Cooling Systems
If concrete tanks are used solely as aging vessels after alcoholic fermentation is complete, the heat capacity of concrete rarely works disadvantageously. However, the story changes when trying to use them as fermentation vessels. Given this reality, most recently constructed concrete tanks are actually equipped with cooling devices.
Concrete tanks are fundamentally insensitive to temperature changes and have characteristics that make them less susceptible to short-term, small-range temperature fluctuations. However, when temperature changes are large and continue for several days, as during alcoholic fermentation, this characteristic backfires. Concrete warmed by fermentation heat stores that heat, maintaining high liquid temperatures even during the later stages of fermentation when temperatures should normally begin to drop.
Because liquid temperature remains high, alcoholic fermentation proceeds faster. The ability to ferment completely without leaving residual sugar is an advantage. The risk of fermentation interruption is also reduced. However, excessively high liquid temperatures can become disadvantages that outweigh these benefits.
Additionally, concrete tanks, unlike ceramic vessels, are not fired and have vulnerable aspects to temperature changes as a material. When temperature changes exceed a certain range, the risk of cracking increases dramatically.
Due to these circumstances, recent concrete tanks are increasingly incorporating cooling devices called cooling coils.
Convection Does Not Occur
What is particularly often discussed regarding concrete eggs is internal convection. The egg shape is believed by some to be the ultimate shape for efficient liquid convection, which uniformly distributes temperature inside the tank and leads to smooth fermentation.
Certainly, shape is undoubtedly one of the important elements for efficient convection. However, convection cannot be generated by shape alone. Recent research has reported that concrete eggs likely do not contribute to convection of wine inside.
Probably, once convection begins to occur within a concrete egg, it would subsequently be efficiently promoted. However, ironically, concrete eggs are unlikely to generate convection itself due to their characteristics.
Liquid convection requires energy. In the case of wine fermentation, the energy source is the temperature difference between the interior and exterior. However, because concrete has a large heat capacity, even if there is a temperature difference between the inside and outside of the tank, such differences are not immediately reflected. Particularly during fermentation, the concrete itself is warmed by fermentation heat and stores that temperature, further eliminating temperature differences between wine and tank walls.
In terms of convection generation, stainless steel tanks have been shown to produce better results.
Concrete: Similar to Wooden Barrels
When comparing the characteristics of concrete tanks as wine containers with vessels made from other materials, they resemble wooden barrels. This applies to temperature characteristics, but most notably to the presence or absence of oxygen supply from the container.
Oak barrels, which have been used continuously in winemaking facilities both past and present, are well known for supplying oxygen to the wine they contain. This characteristic, which significantly influences wine aging trends, is also cited as an area where oak barrels excel compared to stainless steel tanks.
Concrete is a material with micropores on its surface. When wine is placed in concrete tanks, oxygen contained in these micropores is supplied to the wine. The amount seems to vary depending on the surface condition of the tank's inner walls and material composition, but the tendency is for it to be less than wooden barrels while still being sufficient to significantly impact wine aging. Whether concrete itself is oxygen-permeable is not yet precisely understood.
While there are these similarities, there are also decisive differences. Using wooden barrels inevitably imparts oak and roasting nuances to wine to some degree. Concrete vessels, however, do not have this effect. They can be used as containers that supply purely oxygen alone. Due to these characteristics, some producers believe that using concrete eggs allows for purer expression of wine terroir compared to using barriques (small barrels).
A Reliable Partner for Winemaking
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Does Concrete Change Wine?
If we ask whether wine changes when fermentation or aging vessels are made of concrete, the answer is yes, it changes. Wine does change, but whether this is necessarily only in positive ways as commonly claimed is not always the case.
Multiple factors can be considered as reasons why wines produced in concrete eggs differ from conventional wines. These factors can be divided into chemical factors and physical factors.
Chemical factors include, for example, changes in fermentation behavior due to high fermentation temperatures, changes in the types and quantities of fermentation byproducts, and changes in microbiological activity trends due to persistently high liquid temperatures. Physical factors include changes due to contact with concrete. While none of these changes can be definitively labeled as good or bad, some may require careful consideration. Particularly, attention may be needed for changes thought to result from leaching from concrete.
Certainly, technological advances have reduced problems with leachates from concrete. However, verification results have shown significantly increased content of certain metal ions and inorganic substances in wines produced in concrete eggs, suggesting that leaching may not have been completely eliminated. Additionally, concrete has a high pH, and the possibility of affecting wine in direct contact with it continues to be pointed out unchanged from before. Furthermore, with many wineries postponing adoption due to the high difficulty of cleaning, the possibility that characteristics arising from contaminated concrete are being regarded as wine individuality without being recognized as such is said to be not low at all.
The high degree of freedom in concrete shapes and overall design flexibility can be expected to have positive impacts on winemaking. For example, reducing pump usage frequency, and correspondingly reducing oxygen infiltration, power consumption, and water consumption for cleaning. Additionally, concrete's low CO₂ emissions during its own manufacturing, plus its contribution to reducing the amount of timber harvested for barrel production through replacement of wooden barrels, makes it noteworthy as a container with high environmental compatibility from an industrial structure perspective.
Whether concrete eggs will become golden eggs that produce significant results in future winemaking considering global environmental concerns, or whether they will end as just another trend like before, will likely require more time to determine.
