It is time to shine the spotlight on the mystery of sake brewing.

When you, the lover of sake, understand each step of sake brewing, all the technical terms, like muroka and nama, will become clear.

I also hope that seeing the complexity and precision of sake making will make you appreciate this fascinating brew even more!

1. Rice comes first

Sake brewing starts with rice. Long before the kura (brewery) owner assembles his brewing team for the season, the rice farmers plant foundations of next season’s sake. Sake rice – sakamai – is different from table rice. The stalks are taller, the grains are bigger, and it is harder to grow. Rice affects sake flavour, and breweries try their hardest to secure the required amount of chosen rice variety. They don’t always succeed.

Once rice is deliverd to kura, it is milled to remove the outer layer of proteins and fats, and to expose the starch centre. High starch content encourages fermentation, and fats and proteins can give sake off flavours. The degree of milling – normally between 30 and 65% for premium sake – dictates the resulting grade of sake. The more is removed, the higher the grade, the finer the sake. Sake milling is done at the brewery, or at a specialised milling plant.

After milling, brewers leave rice sitting for a couple of weeks, to absorb ambient moisture . Once it is ready to use, it is washed to remove milling powder still clinging to it, carefully soaked to absorb a little more water, and finally steamed.

Steaming is done on the morning of the first day of the brewing cycle. Once rice is steamed and ready to go, it all begins!

2. Koji – the essential sake brewing step

Sake brewers have a motto: “Ichi: koji, ni: moto, san: zukuri”. It translates as “first koji, then the yeast starter, then fermentation”, denoting the order of importance of each in sake making.

Koji mould (Aspergillus Oryzae) is a friendly fungus that has been used to ferment food in Asian cooking for centuries. Most people have eaten food made with koji mould: miso, soy sauce, tempeh. Its role in sake making is to produce enzymes that will convert starches in rice into sugars. This is crucial. The sake yeasts cannot process the long carbohydrate chains of rice grains. Something needs to break them down into simple sugars. In beer brewing, that job is done by grains themselves during the malting stage. Grains naturally contain enzymes that can start the starch to sugar conversion. Sake rice, however, is milled, and all such anzymes are removed.

Once the rice has been steamed for the first time, it is taken to a temperature and humidity – controlled room koji muro, and koji spores are sprinkled all over it. Over the next 40-45 hours, the koji spores propagate on the surface of the rice, creating a characteristic white frosting. Rice with this mouldy frosting is called koji (and the spores themselves are called kojikin).

This step is deceptively simple. But the way the mould propagates over the rice grains has a dramatic effect on the way sake ferments and, therefore, tastes. Koji is drawn to water. Skilled brewers will tweak the ambient humidity, reducing it so that the mould grows towards the moist grain centre, or increase it, so that the mould stays on the surface of the rice.

Once koji is ready, it is time to start the moto, the yeast starter (also known as shubo, the mother of sake).

3.The yeast starter – Moto – Shubo

Once the first batch of koji is ready, the brewers get the starter tank going. Koji – the mouldy rice – and freshly steamed rice are mixed with water and sake yeast. A little bit of lactic acid is added, too, to protect the sake yeasts’ environment from stray bacteria and wild yeasts.

The addition of lactic acid at the beginning didn’t happen until 1911. Until then, natural lactic bacterial fell into the tank from the surrounding air and slowly propagated, creating environment safe for sake yeasts. Addition of lactic acid has revolutionised sake making. Adding lactic acid gave brewers more control over the brewing process, helping them produce more consistent results. Also, it has cut the moto development time from 4 weeks to 2.

The moto is left to its own devices for two weeks, while yeasts multiple. During this time, koji mould continues to convert starches into sugars, to feed the yeasts. This detail makes sake brewing unique. In beer brewing, malting and fermentation happen in stages, but in sake brewing these processes take place at the same time. It is called multiple parallel fermentation.

After two weeks, there will be enough yeast cells in the starter tank to cope with larger quantities of raw materials, so the batch is transferred to a bigger fermentation tank.

4. Main fermentation batch – Moromi

Once the starter is transferred into the larger tank (where the main fermentation will take place until sake is ready for pressing), more koji, steamed rice and water are added 3 times. The additions happen over 4 days, and are called “san-dan-shikomi’. Each time, quantities of ingredients grow bigger.

Once san-dan-shikomi is done, the fermenting sake mash – moromi – will ferment for another 20-40 days in an open tank. During that time, the temperature of moromi will be tightly controlled, to keep it cool. The cooler the temperature, the slower the fermentation, the finer the sake. The sake yeasts are the most comfortable at 28 degrees Celsius. But at such warm temperature, they would propagate too rapidly, only producing alcohol during their short life span. When they propagate slower, they also have time to produce a myriad of fragrance and flavour components – things that make sake delicious. For premium sake, fermentation proceeds slowly and over a longer period, to extract the maximum fragrance and flavour out of yeast.

Along the way, the brewers will measure sugar, alcohol, acidity and amino acid content, to make sure sake ferments according to their secret recipes. The master brewer will stop the fermentation once the chemistry shows the sake is ready. The fermentation is halted by pressing.

5. Post-fermentation steps: pressing, filtering, pasteurising, bottling.

Pressing

Before sake is pressed, it looks white, and a little bubbly, like carbonated milk. Once upon a time sake wasn’t pressed. Rice was a prized commodity, and separating rice solids from the liquid seemed sacrilegious. These days, most sake is clear. Nigori, white sake, is also pressed, and a little of rice solids are allowed back in afterward.

Most sake is pressed using mechanical presses, known as “yabuta”. Yabuta is the name of the most popular brand of sake presses, and like Kleenex, has been appropriated as the name of an object. Yabuta press is like an accordion, whose bellows are expanded and filled with mesh bags full of moromi. Then the bellows are squeezed together, and clear sake runs out.

A traditional box press – fune – is often used by artisanal brewers. Moromi is poured into bags, and the bags are laid inside a large wooden or steel box. Then pressure is applied from the top, to force sake run out of bags. This method produces a finer-tasting sake.

The rarest, and most luxurious, way to extract sake, is to employ the force of gravity. Bags with moromi are simply hung, to let sake slowly drip out. This method, called shizuku, is an expensive way to extract sake, as a lot of liquid is left behind. Yet, it results in sake of grater clarity and refinement. A vertical tasting – sampling the same brand of sake pressed using different methods – will show that differences in resulting flavours are more than subtle. The price of sake will vary accordingly.

Filtering

I’ve marked filtering as an optional step, and indeed, not every brewer will filter its sake. Typically, unfiltered sake is called muroka. Some brewers, however, do not filter the majority of their sake, and do not put the muroka label on the bottle, for example, Nanbu Bijin.

Most brewers will filter sake, to clarify colour and remove heavy flavours, but to a limit! Sake can be over-filtered, so filtering is another step requiring precision. Filtering is done using activated charcoal.

Pasteurising

Pasteurisation of sake is a complex topic. Most sake is pasteurised twice. First time right after filtering, on the way to the storage tank, and second time after maturation, on the way to the bottle (or inside the bottle). Sake that hasn’t been pasteurised is called nama (which means raw in Japanese). Invention of sake pasteurisation in the 16th century (ages before Pasteur discovered it in Europe) revolutionised sake brewing. Sake is pasteurised to deactivate heat and light-sensitive enzymes that could spoil the flavour. Suddenly, sake could retain its fine qualities for a long time, months and even years, without cold storage.

Pasteurisation does kill off enzymes, and there are people who prefer to drink nama. Others say nama-zake is unsettled, and confused, and lacks the refinement of pasteurized sake.

What’s better? The two are very different. Nama-zake has effervescent, jubilant character, and tastes quite lively and fresh. It does need extra care – it must always be refrigerated, and needs to be drunk relatively quickly. Pasteurising sake allows more subtle, refined flavours come to the front. My sake sensei John Gauntner says that ‘nama is like a veil – it covers up the sake it is meant to be’.

Nama is fun, and worth trying, but most sake is pasteurised. Also, nama can mean many things – it could mean that sake was pasteurised the first time but not the second, and vice versa. Or it could be that it wasn’t pasteurised at all. There are technical terms for each type, but the topic is worth an article of its own!

Bottling

After pressing, filtering and first pasteurisation, most sake is stored in large tanks for maturation, for anything between months to years (6-8 months is standard). Young sake is quite brash, and maturation allows for flavours to settle. Traditionally, sake is stored in tanks, before it is diluted, pasteurised and finally bottled. These days, some brewers are beginning to mature sake in bottles, believing it yields finer-tasting sake. Storing in bottles does raise the question of sake consistency, as most sake is blended at the end of the season (for the sake of said consistency).

Most brewers will mature in tanks, though, then dilute sake with water to bring the alcohol content to 15-17% (down from 20%). Or not! Undiluted sake indeed exists and is called genshu. Sake brewers dilute sake to enhance the perception of flavours, which higher alcohol content can overpower. After dilution, the sake is pasteurised for the second time (unless it is meant to be nama) and bottled. That’s it. Sake is finished. Some brewers will store it for a little longer, some ship straight away.

A few last words

Phew! That’s a lot of information. Sake making is oh so complex, and each step is done differently by each brewer. My summary of main steps has left out a lot of nuances – something for the next time. A few last words to put the brewing into context. Brewing is done mainly in winter, to take advantage of cold temperatures. Big brewers do brew year around and refrigerate their brewing facilities. Most kura, however, are small, family-run operations. They treasure the walls of their family kura, and will only modernise to a point. Also, traditionally, sake was brewed by farmers, who planted rice from spring through to autumn, and came to kura to work through winters. So sake brewing is indeed a winter pastime. Well, kind of – sake is brewed October to April, in most places.

The first batch of the season is typically dedicated to lower grades of sake. Once the temperature comes down further, ginjo brewing starts. The lower the temperatures, the finer the sake!

Kampai!