Concrete eggs are large egg-shaped vessels (usually 5 to 6 feet tall) used to ferment white wine. Fermenting in concrete has been practiced in Europe for decades, and the practice is now also common in the New World. There are distinct advantages to fermenting wine in concrete eggs instead of oak barrels or stainless-steel tanks. As fermentation gets underway, the oval shape of the egg helps create a vortex, causing the wine to roll in circular arcs, assuring a thorough, active fermentation. The concrete itself holds heat well, so the warmth created by fermentation is not quickly dissipated, and the wine doesn’t experience wide temperature swings. Lastly, concrete is porous like wood, which allows for the gentle introduction of air, softening the wine.