Methods There are some physical methods that act as inhibitors of bacteria such are warming, drying, irradiation or freezing. Chemical methods can be applied to cause the extinction of death of microorganisms or at least eliminate the possibility of reproduction. In the vast majority of foods are natural preservatives, such as many fruits contain organic acids such as benzoic acid or citric acid. For example, the relative stability of the yogurt when compared with the milk is only due to lactic acid produced during fermentation. Some foods such as garlic, onions and spices contain most potent antimicrobial agents, or precursors that are converted to crush them.