Tallow is a rendered form of beef or mutton fat, processed from suet. It is solid at room temperature. Unlike suet, tallow can be stored for extended periods without the need for refrigeration to prevent decomposition, provided it is kept in an airtight container to prevent oxidation. Rendered fat obtained from pigs is known as lard. Industrially, tallow is not strictly defined as beef or mutton fat. In this context, tallow is animal fat that conforms to certain technical criteria, including its melting point, which is also known as titre. It is common for commercial tallow to contain fat derived from other animals, such as pigs or even from plant sources. Tallow is used in animal feed, to make soap, for cooking, and as a bird food. It can be used as a raw material for the production of biodiesel and other oleochemicals. Historically, it was used to make tallow candles, which were a cheaper alternative to wax candles. Before switching to pure vegetable oil in 1990, the McDonald's corporation cooked its french fries in a mixture of 93% beef tallow and 7% cottonseed oil. Tallow is used in the steel rolling industry to provide the required lubrication as the sheet steel is compressed through the steel rollers. There is a trend towards replacing tallow based lubrication with synthetic oils in rolling applications for surface cleanliness reasons. Tallow can also be used as flux for soldering. Tallow is also the primary ingredient in some leather conditioners. The use of tallow or lard to lubricate rifles was the spark that started the Indian Rebellion of 1857. To load the new Pattern 1853 Enfield Rifle, the sepoys had to bite the cartridge open. It was believed that the paper cartridges that were standard issue with the rifle were greased with lard (pork fat) which was regarded as unclean by Muslims, or tallow (beef fat), regarded as sacred to Hindus. Tallow, along with beeswax, was also used in the creation of lubricant for American Civil War ammunition used in the Springfield Rifle Musket. Tallow is used to make a biodegradable motor oil by a Stamford, Connecticut based company called Green Earth Technologies. Hydrogenation is the chemical reaction that results from the addition of hydrogen (H2). The process is usually employed to reduce or saturate organic compounds. The process typically constitutes the addition of pairs of hydrogen atoms to a molecule. Catalysts are required for the reaction to be usable; non-catalytic hydrogenation takes place only at very high temperatures. Hydrogen adds to double and triple bonds in hydrocarbons.  Because of the importance of hydrogen, many related reactions have been developed for its use. Most hydrogenations use gaseous hydrogen (H2), but some involve the alternative sources of hydrogen, not H2: these processes are called transfer hydrogenations. The reverse reaction, removal of hydrogen from a molecule, is called dehydrogenation. A reaction where bonds are broken while hydrogen is added is called hydrogenolysis, a reaction that may occur to carbon-carbon and carbon-heteroatom (O, N, X) bonds. Hydrogenation differs from protonation or hydride addition: in hydrogenation, the products have the same charge as the reactants. An illustrative example of a hydrogenation reaction is the addition of hydrogen to maleic acid to succinic acid depicted on the right. Numerous important applications are found in the petrochemical, pharmaceutical and food industries. Hydrogenation of unsaturated fats produces saturated fats and, in some cases, trans fats.