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Higher alcohol content in a brew

So, perhaps this is a question I should pose into the forum for everyone elses benefit…

Has anyone ever messed around with adding MORE koji and/or yeast to their recipe? I’m no science buff, but wouldn’t adding more koji aid in the breakdown of rice more completely, which the yeast could then process into more alcohol content in the brew?

I’ve been trying to scheme a way to make a higher proof of brew, and this, in addition to fractional freezing of the final product, seems to be the way that I might try and go…


Throwing more koji at a batch of sake isn’t going to increase the alcohol content, enzymes just don’t work that way. When made properly, koji is so enzyme rich that adding just 25% of your total grist as koji supplies more than enough diastatic power to break down all of the rice in your moromi. In fact, part of the reason for pasteurizing sake has to do with deactivating the remaining enzymes after all of the available amylose has been hydrolyzed.

What you’re really asking, part one: So, why doesn’t the rice break down completely?

Answer: For the same reason malt doesn’t. Rice isn’t made of just starch, it contains other proteins and minerals that make up the cell walls and give the grain its structure. Just like spent malt, sake lees are made up of the bits of the rice kernels that no amount of enzymes supplied koji is going to be able to break down. Those sake lees have given up all their goods, just like the spent grain has in a batch of beer.

What you’re really asking, part two: How do I achieve a higher alcohol content in my sake?

Answer: Genshu (undiluted) sake has an alcohol content of up around 20% ABV. That’s as high as the yeast can tolerate before they die by being poisoned by their own waste (alcohol). If you want it to be any higher (whyyyy?), adding more koji or yeast isn’t going to get you there. This is where fractional freezing or distillation comes in.

I’d go for the freezing, if I were going to do it. Sakejack, anybody?

[quote=“Taylor-MadeAK”]What you’re really asking, part two: How do I achieve a higher alcohol content in my sake?
Answer: …whyyyy?[/quote]

I’m just that kinda idiot that wants to see how far I can push the limits of the envelope. I like shochu, but wish it had a bit more body and character. I’ve even mixed it with my brew to try, and didn’t particularly care for the results.

What about starting with a different yeast, or, adding a different yeast (like a distillers yeast) at a later stage in fermentation? As I understand, most of the flavor profile comes from the koji anyhow, so while it will alter the taste of the final product, it shouldn’t be hugely removed… Right?

While the koji does provide a considerable amount of character to the sake, the yeast cannot be discounted entirely. Adding distiller’s yeast later in the process might work, but that means you would have to proportionately increase the amount of rice and koji you add as well. The recipe I use is formulated in such away that there is just enough carbohydrates present for the yeast to hit their alcohol tolerance limit, any more than that would be wasteful and result in overly sweet sake.

Is there a specific formula, calculation, or ratio that you derived this from, or was it more of a fine tuning through trial and error kind of thing…?

Japanese brewers worked out the ratios long ago: 160:100:25.

I thought that was the ratio for water:rice:koji. Where does yeast sit in relation to this? If I add half the yeast (only using distillers or champagne yeast) back at a later stage, without increasing the water, would I have to add half the rice and koji back as well? Can I assume that a different strain of yeast has the same needs and tolerances for carbs? Won’t this upset the balance, and cause the forces of the universe to come crashing down around my sad mortal life in rebuke?

Yeast doesn’t work like that. It’s a living organism that reproduces itself in your moto. Hypothetically speaking, it would be possible to ferment an entire batch of sake - no matter how big - by adding a single viable yeast cell.

Note: I said possible, not practical.

The idea of adding more yeast late in the fermentation to increase alcohol content is fundamentally flawed. The yeast are the workers, but they can do nothing without carbohydrates. If you want to increase the alcohol content of any fermented beverage, not only do you need an alcohol tolerant strain of yeast, but you also need more carbs.

Just a personal suggestion here: have a care how you proceed. Distiller’s yeast, while certainly known for being able to produce a high octane wash, is not necessarily known for contributing particularly pleasant flavors to said wash.

True. And most of my reading has echoed the same. Furthermore, I won’t be distilling out some of the harsher off flavors that are know to be a byproduct, so all the more care is warranted. That’s why I’m leading toward champagne yeast, additional rice, and fractal freezing.

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