The surface of rice grains and the rice germs contain many proteins, fats, minerals, vitamins and other elements that drastically speed up the cultivation of the koji and yeast, which adversely affects the balance and taste of sake. All of these elements are therefore removed through the process of polishing. The resulting sake product is described by the percentage of the grain that remains after polishing. All of Kinshi Masamune’s sake is brewed from rice that has been polished down to a minimum of 70%. The highest quality type of sake, junmai daiginjo, has been polished down to 35%.

A specifically determined amount of rice is first placed in a stainless steel strainer. This is then soaked in 10℃ water and washed for about one minute, after which it is removed so that water can be run over the rice to remove excess bran. The rice is then placed back into the 10℃ water to soak again.
The length of time the rice is soaked depends on the type of rice, the degree of polishing, what it will be used for, and the temperature and humidity of the day on which this is done. High quality rice that has been polished down to 35% absorbs water very rapidly, so the process must be controlled to the second.

Rice that has been washed and soaked is left to sit for one night. The following morning it is placed in a vat and steamed. Water is placed in the bottom of the steaming vat and boiled so that this newly created steam covers the rice.

When making wine, for example, enzymes are added to grapes and the resulting glucose is fermented to create alcohol.
There is no glucose in rice, however, so koji is first added to the rice starch to create glucose. Enzymes are then added and fermentation takes place.
Fine quality koji is necessary for making fine quality sake. Kinshi Masamune places particular importance on this stage of the sake brewing process. Sake factories have a special room, called a muro, specifically for making koji.
The room temperature is kept at 30℃ or above, and the humidity maintained at up to 40%. The koji is spread out on the floor in one room of the muro and later placed on shelves in another.
The steamed rice is cooled to approximately 40℃ and moved to the muro where it is later gathered together, covered with a cloth and left to sit.

Yeast starter is a large culture of pure yeast created for brewing sake.
Lactic acid is first added to prevent the yeast from being contaminated by airborne bacteria.

The sake mash is created by adding steamed rice, koji and water to the yeast starter and allowing them to ferment.
The most prominent feature of creating the sake mash is that the process is done in three stages in order to promote yeast growth.
The mixture of steamed rice, koji and water is gradually added to the yeast starter in three parts.
If the ingredients are all added at once, the yeast starter becomes diluted and the acidity level falls.
This allows airborne bacteria and natural yeast to grow, thus inhibiting the production of sake-brewing yeast.
Gradually adding the steamed rice, koji and water maintains a favorable environment for yeast production and eliminates bacteria.

The brew master checks the glucose levels every day. He carefully inspects the sake mash to determine when the brewing is complete.
The pressing process separates the liquid from the remaining solids (sake lees).
Various pressing methods exist, but at present the most common is to use an automatic pressing machine.
There are special pressing methods for specific sakes such as Junmai Daiginjoshu and nama-genshu (raw undiluted sake).
For these, Kinshi Masamune uses a method that employs hanging cotton bags.
The sake mash is placed into cotton bags that are hung so that the liquid is naturally pressed out by gravity.
Natural pressing creates an elegant and mild taste.