Leuconostoc is a genus of Gram-positive, facultatively anaerobic, coccoid lactic-acid bacteria of the family Lactobacillaceae (formerly Streptococcaceae), occurring in dairy products, fermenting vegetables, sourdoughs and fermented beverages. Heterofermentative species serve as starters and adjuncts for fermented cream, butter (diacetyl aroma), cheese, kefir, buttermilk, sauerkraut and kimchi — producing diacetyl, acetoin and dextran (exopolysaccharide) that shape flavour and texture; Leuconostoc mesenteroides subsp. cremoris is a classic dairy starter. The same dextran production makes them spoilage organisms in sugar-rich products (ropy brine, slimy syrups).