There are many cheese varieties where milk is coagulated by acid instead of the more common practice of using rennet. These cheeses include Cottage cheese, Quarg, and Cream cheeses. Lactic cultures decrease the pH of milk, reducing the charge stabilization of caseins, which facilitates the aggregation of casein particles. These fresh cheeses do not require a ripening period. Acid-coagulated cheeses are characterized by having high moisture content and an acidic flavor. Acid/heat-coagulated cheeses like Ricotta are made by acidifying whey (or milk/whey mixtures) to pH 5.6–6.0 and heating the milk to 80 °C. The milk proteins rapidly denature and flocculate. Queso Blanco cheeses are fresh acid/heat-coagulated cheeses made in Latin American countries. The whey separation step can be performed by centrifugal separators (Cream and Quarg) or by whey drainage from curd particles (Cottage). The manufacture of fresh cheeses has been highly mechanized with the widespread use of processes such as membrane filtration or automated curd washing equipment. The low pH and high lactic acid content ensure product safety but shelf life is usually limited by the growth of yeasts and molds.