Food additives are substances added to food to preserve or to improve its flavour and colour. The old age additives used for preserving food are by pickling with vinegar, salting or sulphur dioxide common in wine. The latest methods apply additives such as acids, anticaking and antifoaming agents, antioxidant, bulking agents, food colouring, colour retention agents, emulsifiers, preservatives, propellants, stabilizers, sweeteners etc. Stabilizers are added to prevent or retard an unwanted change in physical state of food. They are like thickeners and other agents work with emulsifiers to give foods a good texture, like Agar or the pectin used in jam. Food acids, like vinegar and citric acid, are added to make the flavour of foods "sharper", and also act as preservatives and antioxidants. Antioxidants act as preservatives by inhibiting the effects of oxygen on food. Anti foaming agents are used to reduce or prevent foaming in foods. Propellants are any substances used to expel food from its container. Preservative are natural or synthetic chemicals added to foods to retard spoilage, whether from microbial growth, or undesirable chemical changes. Humectant is a hygroscopic substance often used to prevent foods from drying out.