Monday, June 14, 2010

Sake Fermentation and Racking

Sake after primary fermentationWhen we last left off I had just finished adding the final steamed rice and water infusion to my first batch of sake.  After that last addition I stirred the sake once or twice a day for the following six days.  This ensures that the rice, enzymes, and yeast are evenly distributed (allowing the enzymes to continue slowly breaking down the rice starches into sugars and the yeast in turn to ferment those sugars into alcohol).  All this at a lager-like ambient temperature of 50 degrees, which keeps the yeast calm and clean.  Wyeast recommends a minimum temperature of 60 for the sake #9 strain, but the fermentation was so intense at first that I should have used a blow-off tube even with two gallons of head-space.

A sample of unfiltered/unpasteurized 
Sake.After the sixth day of stirring I left the sake alone for an additional two weeks to complete fermentation.  With only a few days of fermentation left I raised the ambient temperature to 53 degrees to encourage complete fermentation.  At that point most of the rice had settled towards the bottom of the fermenter (with just a scattering of grains floating on the surface).

Two weeks after the last day of stirring I pulled a sample to check the gravity and flavor.  The milky liquid was slightly sweet with good body (from the suspended rice particles), the gravity was a shockingly low .994 (less dense than pure water).  Better to have a fully attenuated beverage rather than a sweet Mirin-like result.  It was a bit boozy, but for such a young/strong beverage it was actually pretty pleasant.

Filling the paint strainer up with the 
rice-Sake mixture from the fermenter.Two days later I had time to separate the liquid sake from the spent rice solids.  To accomplish this I had bought a nylon paint straining bag from Home Depot (the same ones some people use to filter hops out of their wort before fermentation).  Traditionally a cotton joso bag is used for this process, but this is a bit tougher to find (and it doesn't have an elastic band at the top to secure it to the bottling bucket).  With the sanitized nylon bag in place on my bottling bucket it was a simple task to scoop the contents of the fermenter into the bag.  I left the last pint or so of thick rice/yeast slurry in the fermenter (it seemed to be stuck to the bottom and I couldn't see any reason to bring it along).

Separating the Sake from the riceI then gathered up the bag and spent ten minutes squeezing (with my well sanitized hands) as hard as I could to extract as much liquid as I could.  The kitchen filled with the intoxicating scent of fruity esters and sweet, grainy alcohol.  The droplets of sake dripping back into the bucket had me a bit worried about oxidation, which might be one of the reasons sake tends to age poorly compared to beer and wine.  It strikes me that there must be a better methods of accomplishing the same result (but I can't think of what it would be).  I kept squeezing until the only thing coming out was a thick starchy liquid.  The rice goo left in the bag can be discarded (although there are apparently a few traditional uses for it).

The spent rice after the Sake was squeezed 
out.The result of my effort was about two gallons of super cloudy sake which I transferred into two 4 L jugs (plus a single 12 oz bottle that I tossed in the fridge for sampling in a few weeks).  The jugs went back into the fridge at 53 then I dropped the temperature to 40 to help it settle for a few weeks before packaging and pasteurization. 

My plan at the moment is to bottle a portion cloudy (Nigorizake), let some settle and dilute with water to reduce the alcohol to ~11% so I can carbonate it, and add bentonite finings to the rest for clear full strength sake (Genshu).  It will be fun to get multiple end products from this batch, especially since it will allow me to compare the different sake styles from the same "mother" batch for comparison.

The sake was fianlly bottled and pasteurized a few weeks later.

Two gallons of Sake resting in the 
fridge.5/22/10 The airlock had a bit of starchy sake in it and fermentation was raging after only 12 hours.

6/05/10 Raised temp to 53

6/10/10 Pulled a sample down to ~.994. Looks like most of the rice has settled out.

6/12/10 Scooped most of the sake/rice mixture through a nylon pain strainer into a bottling bucket. Left a bit of the most yeast/rice heavy sediment behind. Squeezed the bag until I collected slightly more than 2 gallons of sake. Seems like quite a bit of oxidation would occur. The final squeezes looked very milky/starchy. 2L put back at 50 degrees to settle out a bit, 1 bottle stuck in the fridge for samples.


JB in San Diego said...

How sanitized do you think you need to be at this stage? Won't the alcohol provide protection from bad bugs at this point?

As for an easier way to strain the stuff, I'm still waiting for someone to build a home brewed centrifuge. Seems like that would be a great way to improve mash efficiency in beer, too.

MoRdAnTlY said...

perhaps a french press or is it too thick?

The Mad Fermentationist (Mike) said...

Apparently there is still a good chance of infection at this stage, sake is almost always pasteurized once or even twice during the aging process because it lacks the microbial defense hops provide beer (or metabisulfite provides most wines).

A French Press might be the perfect answer, although the bigger the better since you'd have to press more than three gallons of rice/sake slurry. Certainly seems worth a try next time around.

Lee said...

Did you save any un-"filtered" sake? I am a huge fan of Nigori (cloudy) style sakes. i think they lack a little bit of the elegance of the clear sakes, but have such a wonderful creamy nutty character (though, if you tasted the Nogne brewer's sakes you would have learned that it doesn't handle carbonation well).

I'm jealous of your homebrewed sake. I've always wanted to try but I don't want to get past my limits in a small apartment.

abraxas said...

I thought that pasteurization was to kill the lacto bugs and stop the souring. I have some sake I let ferment too long and it is much too sour. This has always surprised me since I always though the alcohol tolerance of most standard lactobacillus strains was way below the 20% or so of sake.

Taylor-MadeAK said...

If you guys can come up with a better way to press sake, I'm sure there are several pro brewers who would love to hear it!

On the largest scale, moromi is pumped from the fermenter into an enormous hydraulic pressing machine that does the work of pressing in a few minutes. Sounds pretty good, right? Using a pump and a sealed machine to minimize contact with air while extracting the liquid from the solids in the shortest time possible? The thing is...many sake brewers feel this is destructive to the overall character of the sake, so they only do it with their cheapest product.

For the special ginjo and daiginjo batches, even breweries that own one of those fancy hydraulic presses will skip that device and go back to the fune when it's time for joso. A fune is a large wooden press for separating the liquid nigorizake from the solid kasu. The moromi is poured into several (sometimes hundreds) cotton joso bags, which are tied off and loaded into the fune and pressure is applied with a screw until no more liquid can be extracted. Sound familiar? Yup! It's a classic fruit press!

Another method, the oldest of the old-school and still employed by some brewers for the absolute finest of their sakes, is drip pressing. It doesn't get any simpler than this: the moromi is poured into joso bags, which are then hung to drip into one or more catch vessels for several days. No outside pressure is applied, just gravity.

With all that in mind, we can draw some conclusions.

First: almost every method results in at least some contact with the air. The take-home message here is that we can relegate concerns about oxidation to the bottom shelf. Sake does oxidize (turns brown, or black in severe cases), but the time required for that kind of damage is much longer than the relatively short period of time we're talking about during joso.

Second: joso happens a little bit before fermentation has come to a complete halt. That means there are still living yeast in the sake to clean up any oxygen picked up during pressing.

Third: the next step in the process is pasteurization. Hot liquids hold dissolved gas very poorly, so any air and residual CO2 dissolved in the sake will be driven out when it's heated for pasteurization.

So, what's the best tool for joso on a homebrewing scale? That depends on the individual brewer (I know some who have even tried drip-pressing with a great deal of success), but in my opinion the best tool is the fune. If you have the money and are handy with carpentry, you can build one. If not, a small fruit press works just dandy if you don't mind loading it three or four times.

@abraxas: Effects of Lactobacilli on Yeast-Catalyzed Ethanol Fermentations. Just like yeast, different strains of lactobacillus have different levels of alcohol tolerance.

The Mad Fermentationist (Mike) said...

Bob, thanks for all the detailed info.

From your guide I’m not clear on the timeline for the next few steps. Now that I have the sake in the jugs, I keep it cold for about 2 weeks, then I pasteurize in the jugs (do I rack off the sediment first?), then wait a couple months before bottling and pasteurizing the bottles? At which point the sake is ready to drink.

Am I on the right track?

Taylor-MadeAK said...

This part of the process is one of those places where you can tweak the final outcome of your sake, Mike. My normal process is to allow the jugs to finish fermenting and settle out for a couple weeks because I like a dry sake. After that, I rack off the sediment into clean jugs, add bentonite slurry, pasteurize, and seal. I give these fined-and-pasteurized jugs of sake a shake once a day for a week, then I let it mature in bulk for around two months before moving on to bottling and re-pasteurizing.

I did say you can tweak your process here. If you wanted a somewhat sweeter finished sake (FG=1.000), you could shut down the fermentation by dropping your refrigerator temperature to around 34ºF, let it settle out, then move on to racking, fining, and pasteurizing.

The sake is ready to drink immediately after the pasteurized bottles cool, though it'll be a bit harsh if you don't let it mature for a couple months first (either in bulk or after bottling).

Jeff L. said...

A bit late to the game... but I've been reading that you can use a cheese press for the sake, which would probably help to prevent the oxidation. Love your blog btw, it's been an inspiration for my fermentation adventures!