Glass containers, when very hot, cannot be cooled abruptly without risk of breaking, due to the thermal shock that occurs, also resulting in the loss of the contents.
Many food products such as jams, drinks or various preparations are put into jars or bottles immediately after cooking or pasteurization. Rapid cooling after cooking or pasteurization is essential to preserve the main qualities of the product, in particular its taste and colour. Some products lose their qualities more easily than others.
In most artisanal canneries, the containers are simply left to cool in the air
ambient; it often takes several hours. Stacking jars or bottles to save space makes cooling even longer and increases the deterioration of the quality of the preserved products.