How sake is made
Sake breweries come in all shapes and sizes, producing varying quantities involving different techniques and technologies along the way. That said, the core stages of sake production have been the same for centuries and are roughly as follows:
Rice is polished - removing the outer layers of the rice kernels, leaving the starchy centre. The extent to which rice is ‘milled’ effect both the flavour and classification of the final sake. Breweries will sometimes purchase pre-polished rice.
Rice is then carefully washed to remove the bran (senmai), and then soaked in water with precision timing so that it absorbs just the right amount of moisture (shinseki). When these processes are done by hand, the weight of the rice must be accurate to within 0.2%.
The soaked rice is drained and covered with a cloth overnight. The following day the rice is then steamed to soften it slightly and make the starch easier for the koji enzyme to break down. Steaming takes place in a large vat called a koshiki for around 45–60 minutes. After steaming the rice is broken up and spread out so it cools to the right temperature depending on the subsequent part of the brew it is used for.
Koji preparation — Rice, being a starchy cereal grain, needs something to break up that starch into fermentable sugars (glucose, specifically), before it can be converted into alcohol.
Unlike beer where the grain is malted, a starch-digesting mould is grown on around a quarter of the total polished Sake rice, by carefully sprinkling spores of the mould (Aspergillus Oryzae) as a fine powder over the steamed, cooled which has been carefully laid out in a sauna-like koji room. The inoculated rice is then carefully rotated and temperature-controlled for 3-4 days.
The resulting mouldy rice is called Koji.
The ingredients - water, steamed sake rice, koji-rice and yeast - are then combined to create the yeast starter mash known as the Shubo or Moto (‘mother’ of sake). The most common, modern method (known as Sokujo) takes around 2 weeks. More traditional methods - like Kimoto, Yamahai or bodai-moto - are more labour-intensive, unpredictable and slower to produce, but often create wonderful results.
The main mash (Moromi) is built on the starter mash in 3 stages over 4 days and left to ferment for around 20-30 days.
The resulting sake is pressed to separate the liquid from the rice lees (or Kasu, in Japanese). Some sake are hung in bags to drip naturally, while most are mechanically pressed in a bit of kit called a fune.
After resting the pressed sake is then (usually) subject to further charcoal filtering.
Most sake is then bottled and then pasteurised before being stored for around 3–6 months. Unpasturised sake is known as Namazake (or Nama)
Finally the Sake re-pasturised, bottled and shipped.
These brewing stages, like the ingredients, remain largely unchanged in recent history. However, within these ingredients and trusted method there lies much room for the curious Toji (head brewer) to experiment, and over the years a vast array of Sake have been developed, refined, classified and eventually regulated.