Some bacteria and yeasts have useful properties. Bacteria can be used to make yogurt, cheese, vinegar, and compost by fermenting milk or plant materials. Yeast can be used to make alcoholic beverages like beer and wine by fermenting plant sugars. Specifically, Lactobacillus bacteria break down lactose in milk to lactic acid to make yogurt, lowering the pH and giving yogurt its distinctive taste. Yeast undergoes aerobic or anaerobic respiration depending on oxygen levels to produce carbon dioxide to leaven bread or alcohol if oxygen is limited.