Organic natural substances (proteins), which are composed of amino acids and are a main component of all living things. In grape seeds they are contained in the pulp of the grape, in dry years more proteins are formed. During fermentation they serve as food for the yeasts. In larger quantities the so-called thermolabile protein causes veil-like, grey turbidity and is removed by means of bentonite. Various protein-containing agents are used to fining and clarifying the wine, including albumin, egg white, gelatine, Hausenblase, lysozyme and casein. All these substances are positively charged electrically and therefore attract negatively charged substances.
If there is too much thermolabile wine protein in the bottle, the two wine faults protein cloudiness and cheesiness can occur. Proteins can cause allergies in humans, some of which can cause strong reactions. From a quantity of 0.25 mg/l in wine, this must therefore be declared on the label. Vegetarians and vegans reject wines treated with protein-containing substances (see Vegetarian Wine). Gluten, which is incompatible with certain diseases, is also a protein, but wine is usually gluten-free. For limit values, see ADI (acceptable daily intake) and a list of all wine ingredients under total extract and agents used in winemaking.