Mesophilic refers to bacteria or cultures that thrive at moderate temperatures, typically between 20°C and 40°C , with optimal activity around 30°C. In cheese making, mesophilic cultures are used for cheeses that do not require high heat during curd development, such as Cheddar, Feta, Cottage Cheese, and Gouda. These cultures primarily aid in acid production, flavor development, and sometimes gas production, depending on the strain.