How is Japanese sake brewed, and what are the main classifications?

Hey, talking about Sake, it's quite interesting. Its brewing process is significantly different from what we're familiar with, like Baijiu, wine, or beer. Simply put, you can imagine it as a magical process of turning rice into alcohol.

How is Sake brewed?

Rice Polishing (Seimai): This is the first and a very crucial step in sake brewing. Brewers polish away the outer layers of the rice grain because these layers contain proteins and fats that can introduce off-flavors to the sake. They only want the starchy core of the rice, known as the 'shinpaku' (white heart). The degree to which the rice is polished is a key indicator called 'seimai-buai' (rice polishing ratio), which we'll discuss in detail when we cover classification.
Washing, Soaking, and Steaming Rice: The polished rice is thoroughly washed, soaked in water for a precisely controlled duration, and then steamed. This process yields rice that is firm on the outside and soft on the inside, preparing it for the next steps.
Koji Making: This is the 'magical' core of sake brewing. Brewers sprinkle a beneficial mold called 'koji-kin' (Aspergillus oryzae) onto a portion of the steamed rice, much like sprinkling pepper. This is then carefully cultivated in a warm, humid room. The role of koji-kin is to convert the starch in the rice into sugar. This is the biggest difference between sake and wine/beer: grapes naturally contain sugar, and beer relies on malt saccharification, whereas sake must 'create sugar' through this koji-making step.
Shubo (Sake Starter) Preparation: The koji rice, steamed rice, water, and yeast are mixed together in a small tank to cultivate a highly concentrated and robust 'yeast army'. This 'shubo' acts as the 'starter' for the main fermentation, determining the vitality of the sake.
Main Fermentation (Moromi): The shubo is transferred to a larger fermentation tank, and the remaining koji rice, steamed rice, and water are added in three stages (a process called 'sandan jikomi'). This process is unique: the koji-kin converts starch into sugar, and simultaneously, the yeast converts that sugar into alcohol. This simultaneous saccharification and fermentation is known as 'multiple parallel fermentation' (heiko fuku hakko), which is unique to sake and the secret behind its natural alcohol content reaching around 20%.
Pressing, Filtering, and Pasteurization: After fermentation, the porridge-like 'moromi' is pressed, often using cloth bags, to separate the clear sake liquid from the white sake lees (Sake Kasu, which is also delicious and can be grilled or used in cooking). Depending on the desired outcome, the sake may then undergo activated carbon filtration, one or two rounds of low-temperature heat pasteurization (called 'hi-ire'), and finally, a period of maturation to mellow its flavors before bottling.

What are the classifications of Sake?

This is what most people are curious about, as the myriad terms on sake labels can be confusing. The most common classification method is based on 'how much the rice has been polished' and 'whether a small amount of distilled alcohol has been added'.

Firstly, all sake is divided into two main categories:

Junmai-shu (Pure Rice Sake): The ingredients list only includes rice, water, and koji. It's brewed purely from rice, so you can typically taste the original rice flavor more distinctly, offering a richer, fuller-bodied taste.
Honjozo-shu: In addition to rice, water, and koji, a small amount of 'brewer's alcohol' (distilled alcohol) is added. Don't mistake 'alcohol' here for a low-quality blended spirit; it's not! The amount added is very small, and its purpose is to better 'draw out' the aromas from the rice, making the sake lighter, smoother, and more aromatic.

Within these two categories, sake is further classified from basic to premium based on the rice polishing ratio (seimai-buai):

Rice Polishing Ratio Requirement	Junmai Category	Honjozo Category	Flavor Characteristics
50% or less	Junmai Daiginjo	Daiginjo	The pinnacle of sake. The most opulent and delicate aromas, with very distinct fruity and floral notes, and a silky smooth texture.
60% or less	Junmai Ginjo	Ginjo	The entry point for premium sake. Distinct fruity and floral aromas (known as 'ginjo-ka') begin to emerge, with an elegant taste.
70% or less	Tokubetsu Junmai	Tokubetsu Honjozo	'Tokubetsu' (special) indicates the use of superior rice or a more unique brewing method, offering a more refined flavor than the basic types below.
No specific requirement	Junmai-shu	Honjozo-shu	Basic types. Junmai-shu has a rich rice flavor, while Honjozo-shu is refreshing. These best represent the brewery's fundamental style.

Simply put: Daiginjo > Ginjo > Honjozo/Junmai-shu. Generally, the longer the name, the higher the grade.

Besides this main classification, you might also encounter some other terms:

Namazake (Unpasteurized Sake): Sake that has not undergone any heat pasteurization. Like fresh juice, it has a lively and fresh taste, but it must be kept refrigerated at all times and has a shorter shelf life.
Genshu (Undiluted Sake): Sake that has not been diluted with water after pressing. It has a higher alcohol content (usually 17-19%) and a very rich, potent flavor.
Nigorizake (Cloudy Sake): Sake that has been coarsely filtered, leaving some white rice sediment in the liquid. It appears cloudy and has a milky, often sweeter, taste.

Once you understand these basics, you won't be bewildered by sake labels when you visit an izakaya or choose a bottle. If you're trying sake for the first time, I personally recommend starting with 'Junmai Ginjo'. Sake at this level usually offers a good balance of fruity and rice aromas, is moderately priced, and is the easiest way to appreciate the wonderful qualities of sake.