Mannitol is a higher quality alcohol or sugar alcohol. In nature, the substance is found mainly in algae, figs, olives and fungi, as well as in the sap of larch and manna-ash. It is artificially produced from fructose and serves as a sugar substitute in the food industry. In winemaking, the wine defect mannitic sting can occur during malolactic fermentation (biological acid breakdown). In this process, heterofermentative lactic acid bacteria convert fructose into carbon dioxide, mannitol and often also acetic acid (a redox reaction of fructose). Wines low in acid and alcohol, which have been insufficiently sulphurised, are particularly at risk. The mannitol sting is expressed by a typical bitter, disgusting taste.