MOCHI

Mochi (餅?) is Japanese rice cake made of mochigome, a short-grain japonica glutinous rice. 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. Similar snacks are prominent in Hawaii, South Korea, Taiwan, China (where it is called 麻糬, Hokkien môa-chî or Mandarin máshu, tang yuan), Cambodia, Vietnam and the Philippines (where it is called maha), Thailand, and Indonesia (where it is called kue moci and has become specialty of Sukabumi town).

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 lack of amylose in starch and is derived from short or medium japonica rices. The protein concentration of the rice is a bit higher than normal short-grain rice and the two also differ in amylose content. In mochi rice, the amylose content is negligible which results in the soft gel consistency of mochi.

Mochi's characteristic chewiness is due to the polysaccharides in it. The viscosity and elasticity that account for this chewiness are affected by many factors such as the starch concentration, configuration of the swollen starch granules, the conditions of heating (temperature, heating period and rate of heating) as well as the junction zones that interconnect each polymer chain. The more junction zones the substance has, the stronger the cohesiveness of the gel, thereby forming a more solid like material. The perfect mochi will have the perfect balance between viscosity and elasticity so that it is not inextensible and fragile but rather extensible yet firm.

Many tests have been conducted on the factors that affect the viscoelastic properties of mochi. As puncture tests show, samples with a higher solid (polysaccharide) content show an increased resistance and thereby a stronger and tougher gel. This increased resistance to the puncture test indicate that an increase in solute concentration leads to a more rigid and harder gel with an increased cohesiveness, internal binding, elasticity and springiness which means a decrease in material flow or an increase in viscosity. These results can also be brought about by an increase in heating time. Sensory assessments of the hardness, stickiness and elasticity of mochi and their relationship with solute concentration and heating time were also performed. Similar to the puncture test results, sensory tests also determine that hardness and elasticity increase with increasing time of heating and solid concentration. However, stickiness of the samples increase with increasing time of heating and solid concentration until a certain level, above which the reverse trend is observed. It is important to understand these relationships because too hard or elastic of a mochi is undesirable, as is one that is too sticky and will stick to walls of the container.


SOURCE : http://en.wikipedia.org/wiki/Mochi