Wednesday, March 9, 2011

Bourbon Aged Russian Imperial Stout

Although not my favorite style in the world, a well made, nicely balanced bourbon barrel aged Russian Imperial Stout definitely holds my respect.  It’s a curious style that’s captivated my interest, not only because I like how the bourbon, roast, and sweetness meld, but because the commercial offerings vary wildly and they’re often regarded by beer connoisseurs as the best in the world (currently 13 of the top 25 beers on Beer Advocate are one form of an imperial stout or another).  

Last year, when we brewed our Imperial Autumn Maple, we discovered that the house yeast used by the Bruery is capable of extremely high attenuation rates (the gravity plummeted with that beer from 1.099 to 1.001).  Knowing this, along with the rumor that the Bruery uses this strain to ferment out their near 20% abv RIS Black Tuesday, we decided to experiment with the yeast and see if we could come up with our own RIS… hopefully with an ABV upwards of 17%.  Brewing such large beers can be a daunting task though, and, even though there are numerous accounts of how some commercial breweries choose to do so, when designing the recipe we decided to accept a few tips and forgo others.  

Especially in high gravity worts, yeast is your critical factor.  Most breweries who attempt to make 15% or higher ABV beers start with initial gravities around 1.100 and then continue to feed the yeast sugar throughout the secondary fermentation for three reasons: 1.) to avoid initially high osmotic pressures, 2.) to force the yeast to convert the more complex long chain dextrins before working on the simpler sugar additions, and 3.) to keep the yeast active in the increasingly toxic environment.  I’d like to say that we factored all of these considerations into our design, but since we knew we were working with an extremely high attenuating strain of yeast, we decided to roll the dice, forgo the osmotic pressure issue, and brew up a starting gravity of 1.135.  

As for creating easily fermentable sugars, we had a tough time deciding at what mash temperature to conduct the main saccharification rest.  On one hand, we wanted a wort with as relatively simple sugars as possible so that the yeast would have an easier time chewing through them (requiring a low mash temp), but on the other, we were dealing with a yeast that had a history of completely fermenting out high gravity worts and we didn’t want to be left with a thin bodied RIS.  If we mashed with too high of a temp, the yeast could have struggled with the longer chain dextrins and we might have ended up with a syrupy sweet mess.  In the end, we decided that doughing in at 146 degrees and then quickly raising our HERMS temp control to 153 would work out well.  With 30lbs of grain in the mash tun, raising the temp via the HERMS recirculation would not be an instant change.  The grains on the top would hit 153 quickly while those on the bottom would be slower to adjust.  Overall, it took about 15 minutes for the system to reach equilibrium which hopefully resulted in a good balance of simple and slightly more complex sugars.

Although we didn’t want to feed our beer up from 1.100, we did decide to make one sugar addition during primary fermentation.  After a vigorous nine days of fermenting, signs of slowing started to occur.  Based on experiences with the yam beer, we knew that this yeast would take about a month to slowly finish up the remaining sugars and so rather than having the highly alcoholic beer sit on the autolyzing yeast cake for the duration, we racked the beer over to mix with 1 lb of maple syrup patiently awaiting its demise in the secondary.  The suspended yeast made quick work of the new sugars and within 3 hours, a small krausen had formed on the surface.  

Finishing Hydrometer @ 1.024
A month later when we racked the beer into a keg for long term maturation, the gravity was down to 1.024.  To simulate aging the beer in a bourbon barrel, we also added in oak staves and about 2.5 cups of Makers Mark.  I’ve heard rumors that about 3% of Black Tuesday’s ABV can be attributed to remnant bourbon in the barrels, but in order to achieve that same 3% addition with our beer, we would have had to add about 11 cups of bourbon.  That seems excessively high, so rather than just making the assumption, we tested different amounts in a sampling glass before scaling up to the full addition.  At 6ml per ¾ cup, the flavor was just starting to make an appearance and so we decided to scale up that amount to 2.5 cups for the 5 gallon batch.  In another month or so, we’ll taste test and add more as necessary.  I’m expecting the beer to be able to handle probably another 2 – 3 cups and with that amount, we should finish up with a brew right around 17% abv.

 Bourbon Aged Russian Imperial Stout

Recipe Specifics
Batch Size (Gal): 6.0
Total Grain (Lbs): 30.13
Anticipated OG: 1.147
Anticipated SRM: 81.0
Anticipated IBU: 97.4
Wort Boil Time: 90
Anticipated ABV: ~16.0% before bourbon, 17%+ after
Actual ABV: 16.1% after fermentation, final TBD

64.3% - 20.0 lbs Maris Otter
12.9% - 4 lbs Munich Malt
5.6% - 1 ¾ lb Roasted Barley
3.2% - 1 lb Flaked Barley
3.2% - 1 lb Maple Syrup
2.4% - ¾ lb Black Patent
2.4% - ¾ lb Chocolate Malt
1.6% - ½ lb CaraMunich 40
1.6% - ½ lb Special B
0.4% - 2 oz. Dark Molasses

80 grams Magnum (Pellets, 12.5% AA) @ 60 minutes

Bruery house strain – cultured from a bottle of Orchard White, grown up for our batch of Exploited Belgian Pale, and then pitched directly onto yeast cake.

Water Profile and Additions
Charcoal filtered Seattle water
Mash Additions: 1.9 g/g baking soda and 0.25g/g chalk
Boil Kettle Additions: 1.0 g/g calcium chloride and 0.35 g/g Epsom salt (based on final volume of 6 gallons)

Mash Schedule
Doughed in at 146
Immediately raised temp to 153 via HERMS, rested there for 90 minutes
15 minutes @ 168
Sparged with 172 degree H2O

Brewed on 1/29/2011 with Blake

Doughed in to hit 146 as initial temp.  Immediately raised temp on HLT so HERMS was recirculating at 153.  With 30lbs of grain, the average temp of the mash for the first 15 minutes was probably right around 149.  Mashed for 90 minutes before raising the temp to 168.  After a stabilized temp was reached (30 minutes), temp was raised to 172 where we started the sparge.

Colorful foam right before the boil
Collected 8 ½ gallons of 1.126 wort.  Since our boil kettle is only 10 gallons, we had to boil for an hour to reduce the volume before we could add more.  At that point, we sparged another gallon of 1.065 wort.

Whirlflock, molasses, and yeast nutrient added at 15 minutes.

Chilled down to 66° and racked directly onto yeast cake.  After 60 seconds of pure O2, carboy was then placed in fermentation chamber set to 66°.  11 hours later, massive blow-off was occurring.  We removed the blow off hose and gave the wort an additional 30 second dose of pure O2. 

2/8/2011 – Gravity down to 1.034 and there’s a bubble coming out of the blow off hose about every 2 seconds..  Taste is still very sweet and thick.  Racked over to secondary with 1 lb (12 oz. by volume) of grade B maple syrup.

3/6/2011 – Gravity down to 1.024.  Racked over to keg and added 2.5 cups of Makers Mark and 3 bourbon soaked oak staves (about 29 sq. in. of surface area).  Will taste again in a month and add more oak and bourbon as necessary.

The body at this point has really thinned out and is just about perfect for an RIS.  There’s also a lot of boozy heat though that hopefully will mellow considerably in the months to come.  Although I like the mouth feel of the beer right now, the yeast really kicked off a lot of phenolics that I was not expecting.  I knew that it’s a Belgian type strain, but in our Imperial Autumn Maple, you don’t pick up on it that much.  With this beer, I was hoping that the roast notes would hide the phenolics a lot more than they apparently have.  We might have to rename this to a Bourbon Aged Belgian Imperial Stout…

4/28/11 - Sampled beer and there was very little bourbon flavor.  Added another 1 3/4 cps.  This brings the AVB up to about 17.2%. 

11/21/11 - Sampled beer again and it's amazing how the Belgian character has's nearly gone.  The bourbon and oak character still was below where I wanted it, so I added 0.6 oz (19 cubes) of American heavy toast oak and 12 oz. of Maker's Mark.

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