page_title: Mochi
section_title: Chemistry and structural composition of glutinous rice
hierarchical_section_title: Mochi / Chemistry and structural composition of glutinous rice
context_page_description: Mochi is Japanese rice cake made of mochigome, a short-grain japonica glutinous rice, and sometimes other ingredients such as water, sugar, and cornstarch. The rice is pounded into paste and molded into the desired shape. In Japan it is traditionally made in a ceremony called mochitsuki. While also eaten year-round, mochi is a traditional food for the Japanese New Year and is commonly sold and eaten during that time.
  Mochi is a multicomponent food consisting of polysaccharides, lipids, protein and water. Mochi has a heterogeneous structure of amylopectin gel, starch grains, and air bubbles. This rice is characterized by its low level of amylose starch, and is derived from short- or medium-grain japonica rices. The protein concentration of the rice is higher than that of normal short-grain rice, and the two also differ in amylose content. In mochi rice, the amylose content is negligible, and the amylopectin level is high, which results in its gel-like consistency.
  Mochi is similar to dango, but is made using pounded intact grains of rice, while dango is made of rice flour.
context_section_description: Amylose and amylopectin are both components of starch and polysaccharides made from D-glucose units. The big difference between the two is that amylose is linear because it only has αlpha-1,4-glycosidic bonds. Amylopectin, though, is a branched polysaccharide because it has αlpha-1,4-glycosidic bonds with occasional αlpha-1,6-glycosidic bonds around every 22 D-glucose units. Glutinous rice is nearly 100% composed of amylopectin and almost completely lacks its counterpart, amylose, in its starch granules. A nonglutinous rice grain contains amylose at about 10-30% weight by weight and amylopectin at about 70-90% weight by weight.
  Glutinous or waxy type of starches occur in maize, sorghum, wheat, and rice. An interesting characteristic of glutinous rice is that it stains red when iodine is added, whereas nonglutinous rice stains blue. This phenomenon occurs when iodine is mixed with iodide to form tri-iodide and penta-iodide. Penta-iodide intercalates between the starch molecules and stains amylose and amylopectin blue and red, respectively. The gelation and viscous texture of glutinous rice is due to amylopectin being more hygroscopic than amylose, thus water enters the starch granule, causing it to swell, while the amylose leaves the starch granule and becomes part of a colloidal solution. In other words, the higher the amylopectin content, the higher the swelling of the starch granule.
  Though the amylopectin content plays a major role in the defined characteristic of viscosity in glutinous rice, factors such as heat also play a very important role in the swelling, since it enhances the uptake of water into the starch granule significantly. The swelling increases at about 10% in volume per 10 °C temperature increase.
  The high amylopectin content of waxy or glutinous starches is genetically controlled by the waxy or wax gene. Its quality of greater viscosity and gelation is dependent on the distribution of the amylopectin unit chains. Grains that have this gene are considered mutants, which explains why most of them are selectively bred to create a grain that is close to having or has a 0% amylose content. The table below summarizes the amylose and amylopectin content of different starches, waxy and nonwaxy:
  The soaking of the glutinous rice is an elemental step in the preparation of mochi, either traditionally or industrially. During this process, glutinous rice decreases in protein content as it is soaked in water. The chemicals that make up the flavour of plain or "natural" mochi are ethyl ester acetic acid, ethanol, 2-butanol, 2 methyl 1-propanol, 1-butanol, 3-methyl 1 butanol, 1-pentanol and propane acid.
  Mochi is usually composed solely of glutinous rice, however, some variations may include the additions of salt, spices and flavourings such as cinnamon (cinnamaldehyde). Food additives such as sucrose, sorbitol or glycerol may be added to increase viscosity and therefore increase gelatinization. Additives that slow down retrogradation are not usually added since amylopectin has a very stable shelf life due to its high amylopectin content.
caption: The structure of amylopectin with alpha 1-4 and alpha 1-6 glycosidic bonds