Sodium hydroxide is also known as caustic soda. Sodium hydroxide is used in many industries, mostly as a strong chemical base in the manufacture of pulp and paper, textiles, drinking water, soaps and detergents and as a drain cleaner. Sodium hydroxide is used to digest tissues with farm animals. Strong bases attack aluminium. Sodium hydroxide reacts with aluminium and water to release hydrogen gas. Sodium hydroxide is traditionally used in soap making. For the manufacture of biodiesel, sodium hydroxide is used as a catalyst. Food uses of sodium hydroxide include washing or chemical peeling of fruits and vegetables, chocolate and cocoa processing, caramel coloring production, poultry scalding, soft drink processing, and thickening ice cream. Olives are often soaked in sodium hydroxide for softening. Sodium hydroxide is frequently used as an industrial cleaning agent where it is often called "caustic soda flakes"