The use of concrete wine vessels has met the increasing demand for wine consumption to satisfy the palate of both wine experts and wine newbies. Highly used until the Second World War, concrete had been abandoned in steel and oak favor. The egg shape is not entirely new. The amphorae of Greek and Roman times were a precursor to this shape—they were eggs with a midriff bulge. Even today, in Georgia and parts of Italy, wineries are using qvevri (very large terracotta amphora-like tanks that are buried in the ground) to produce wines that are unique in color, interesting in taste and quite delightful.
But why concrete? What makes a vessel like a concrete egg better than stainless steel or oak barrel? Concrete has some unique characteristics that make it the perfect material for making wine. Its porosity and its entrapped air allow micro-oxidization: the wine breathes much like what happens with oak barrels, but without leaving any flavors behind. This slow oxygenation is helpful in preserving wines aromatics, producing and improving the overall mouthfeel. Concrete is also a great insulator, protecting the fermentation process better than any other material and keeping the ideal temperature for fermentation.
The concrete egg’s shape is favorable to a easier and effective wine circulation during the fermentation, which enables the wine to develop a complex taste through its constant contact with lees. The French company Galileo has designed spherical lightweight concrete vats, developing a principle comparable to that of the igloo, with a thermoregulating circuit directly integrated into the concrete’s mass.
Functioning of a concrete egg (picture courtesy of www.wine-egg.com)
A typical concrete wine vessel has a multilayered structure with different mix designs interlocked to provide strength, resistance to cracking, resistance to chemical deterioration (for example by incorporating nanoparticles such as colloidal silica) and the needed thermal stability for an optimal wine fermentation with no additional cooling. The use of ultra-lightweight concrete, usually quite 10 cm thick, is widespread to reduce the weight of the vessels. The outer layer could be a sprayed cementitious face coat to give a beautiful smooth appearance in any desired color. The second layer a thick layup of high-tech glass-fiber reinforced concrete to provide great strength and crack resistance. The inner, thickest layer usually is a traditional cast concrete with no additives, free of coatings to avoid the release of potentially harmful compounds (for example from epoxy resins), just like clay amphoras.
There are not only benefits in using concrete vessels, as they also have some disadvantages. Being concrete’s mass beneficial for good winemaking (enabling long and slow changes in temperature), because of the tank’s weight, a winery shouldn’t plan on moving it very often. One major concern is that after use, cleaning concrete needs to be done carefully. Hot water is not recommended, especially if there are any metal parts imbedded or attached to the tanks. The tank can crack if a too great temperature difference occurs between metal and concrete. Aggressive cleaning measures such as power washers cannot be used. Even strong bristled brushes can create problems on tank surfaces. Instead, alkaline cleaners such as peroxycarbonate are frequently used.
EFFECTS ON WINE COMPOSITION
The concrete egg’s shape is favorable to a easier and effective wine circulation during the fermentation, which enables the wine to develop a complex taste through its constant contact with lees. The vessels used for winemaking do not impact the alcohol, color intensity or phenolic content of the wines, and this is a little surprising, that oxygen is able to permeate through concrete, but not through stainless steel. As a result of oxygen permeation through concrete, the tannins in wine are softened and the wine develops a richer body and more complex taste. Unlike wooden barrels, which have similar influence on wine, concrete does not add any vanilla or other spices’ tastes coming from oak but it enables the winemaker to preserve fruity characteristics of wine without adding additives to preserve wine’s quality and taste. The release of inorganic compounds from concrete, such as silicon, sodium and magnesium has a direct effect on lowering the titratable wine acidity (for a complete chemical comparison among wines fermented in different vessels, check the article of M. Gil i Cortiella, C. Ubeda, J.I. Covarrubias, V.F. Laurie and Á. Peña-Neira, Chemical and Physical Implications of the Use of Alternative Vessels to Oak Barrels during the Production of White Wines, Molecules (2021), 26, 554, https://doi.org/10.3390/molecules 26030554). Moreover, it seems that concrete vessels favor the precipitation of calcium salts during winemaking, since the concrete vessel’s wines had the lowest calcium content..