concrete, popular since the 19th century for the construction of large fermentation vessels and tanks for storage and ageing, it was upstaged by the introduction of shiny stainless-steel vats from the 1970s onwards. Nevertheless, concrete’s greater thermal inertia, longevity, cost-effectiveness, and overall influence on wine quality are still appreciated by many top producers, including Bordeaux’s petrus, and the material is experiencing a renaissance. Traditionally lined with epoxy resin to prevent direct contact between the concrete and the wine and to make cleaning easier, especially the removal of tartrate crystals, concrete tanks do have the potential disadvantage of allowing very little oxygen exchange, which is important in the evolution of tannins. Some producers therefore prefer unlined concrete for its greater oxygen ingress. Since the early 2000s, so-called concrete eggs have been gaining in popularity among a small group of producers around the world because the shape not only offers a high level of contact between the wine and the lees but also appears to encourage convection currents that improve fermentation kinetics and reduce the need for bâtonnage. They range in size from around 500 to 1,500 litres (130–400 gal) and are usually unlined but treated with tartaric acid solution before use. Early adopters include Michel chapoutier, South Africa’s Eben Sadie, and Alfred Tesseron at Ch Pontet-Canet.