In addition to producing desirable flavors, fermentation can control microbial growth. It functions through anaerobic metabolism of sugars by acid-producing bacteria that lower the pH of the substrate, the foodstuff. A pH below 5.0 restricts growth of spoilage microorganisms. Acid products that result from fermentation contribute to a lower pH and reduced action of microorganisms. Foods that are acidified and heated may be packed in hermetically sealed containers to prevent spoilage by aerobic growth of yeasts and molds.