Concrete is a semi-porous substance, which allows for micro-oxygenation and does not impact the wine’s aromas, as well as its flavors. Concrete shaped eggs are beneficial to wine aging in numerous ways. Benefits include temperature regulation, as well as the suspension of leftover yeast due to fermentation leading to a softer acidity in the wine.
The leftover yeast creates an enhanced richness in flavor and texture for wines, which helps with the overall stability and age of finished wine.
Source: Barrons, November 2019