slower burn rate. This reduces the risk of cracking propellant grains. Sugars with a double bonded oxygen, such as fructose and glucose, are less thermally stable and tend to caramelize when overheated. Sugars that only have alcohol groups, like sorbitol, are much less prone to this decomposition. Some other commonly used sugars include erythritol, xylitol, lactitol, maltitol, or mannitol. Oxidizers The oxidizer most often used in the preparation of sugar motors is potassium nitrate (KNO3). Other oxidizers can be used as well, such as sodium and calcium nitrates as well as mixtures of sodium and potassium nitrate. KNO3 can be acquired through purchasing a granular "stump remover" from stores that carry garden supplies. Other rarely used oxidizers are ammonium and potassium perchlorate. Two main issues need to be addressed with respect to the oxidizer if one is using potassium nitrate. The most important issue is the purity of the material. If a purchased material does not perform satisfactorily it may be necessary to recrystallize the KNO3. The second important issue with respect to the oxidizer portion of a propellant is its particle size. Most propellant makers prefer their KNO3 ground to a small particle size, such as 100 mesh (about 150 μm) or smaller. This can be done using a coffee grinder. Rock-tumblers can also be used to mill into a fine grained well mixed powder. Additives Additives are often added to rocket propellants to modify their burn properties. Such additives may be used to increase or decrease the burn rate of the propellant. Some are used to alter the color of the flame or smoke produced. They can also be used to modify a certain physical property of the propellant itself, such as plasticizers or surfactants to facilitate the casting of the formulation. There are many types of experimental additives; the ones listed here are only the most commonly used. Metal oxides have been found to increase the burn rate of sugar propellants. Such additives have been found to function best at levels from 1 to 5 percent. Most often used are iron oxides. Red iron oxide is used most often as it is somewhat easier to obtain than the yellow, brown, or black versions. Brown iron oxide exhibits unusual burn rate acceleration properties under pressure. Carbon in the form of charcoal, carbon black, graphite, etc., can be and sometimes is used as a fuel in sugar formulations. Most