Kernel - x Kanpai Sake Kasu Lager 30L Keykeg

Our friends and neighbours at Kanpai Sake brew delicious craft sake and have given us their Sake Kasu, which is the lees of the sake fermentation, what’s left after the liquid (sake) is removed. It’s made up mostly of what remains of the rice that fuels the sake fermentation, along with sake yeasts, and whatever else a fermentation like this contains (we are not exactly sure. Read more on their process here). It is really delicious (it is used as an ingredient or condiment, and to marinade / pickle things in), and is quite intense. Which makes the delicacy and poise of the finished beer quite surprising to us.

We brewed our house lager as co-fermentation of our lager yeast and the sake kasu. (It was about 100kg of sake kasu added to the FV). We fermented it as we would our lager. (We have a separate barrel fermentation of the sake kasu in our barrel room, which will be part of a future release).
Although the pitching of both were simultaneous, it feels like their effects are sequential. Aromatically is a clear lager profile, a touch more fruity than usual, even a little rice? The middle presents again as a classic lager, the body has a touch more heft. The finish is where the sake kasu appears, first as a particular fruitiness (plums?) / sweetness, then as an umami character (divorced from anything savoury or salty), then as a dry finish.
The sake characteristics are recognisable here. We dialled down the bitterness to allow the sake finish to stake its claim – a good lager would usually have a crisp finish provided by the beer’s natural acidity, but the sake kasu here seems to have changed that balance, ending things with a dry minerality.

This all sounds quite complicated, but the beer itself is pretty simple, straightforward and enjoyable on all levels. As the sake kasu has not been through any pasteurisation, we imagine all the yeast, koji, bacteria etc from the breaking down of the rice starch and from the sake fermentation are likely all still present in the beer, and things may well evolve from here. This probably depends on how these microbes who have evolved on a diet of rice react with the barley substrate of the beer.