Obligatory oh God I don’t blog enough. No excuse there really, I have a tendency to put a ton of work on my plate, and then when it comes time to prioritize that work I fall short. Hell, I was even considering starting another website, but thankfully /u/chino_brews of the /r/homebrewing subreddit talked me out of it. I’m still toying with the idea, but I need to prioritize some other work.
We left our hero hopped up and bitter, for a RIS anyways. Now that we have our fermentables and our bitterness, we have two primary ingredients left to discuss. Water is going to be talked about in another post, since it really does need to be a post of its own, which leaves us with today’s topic: Yeast.
Yeast is a topic that comes up a lot (relatively speaking) when discussing big beer styles like barleywine or imperial stout, and understandbly so. The high OG and osomotic pressure can be daunting, and stressing the yeast causing off flavors is a legitimate concern. So making sure you choose a yeast that can handle the beer you’re brewing, and then pitching a healthy culture and amount of that yeast, is pretty important. That aside, we get into issues like attenuation and flavor, esters, yeast flavor contributions, etc. Yeast is important, I’m preaching to the choir, so let’s dive into what our commercial and homebrew examples are using.
|Ten Fidy||Old Rasputin||KBS||Serpent Stout||Yeti Imperial Stout||Expedition Stout|
|Yeast||WYeast 1056||WYeast 1056||WYeast 1056||WLP007 (Estimation, Dry English Yeast)||WYeast 1056||Bell’s House Yeast|
|NHC 2005||NHC 2006||NHC 2007||NHC 2011||NHC 2012||NHC 2013|
|Yeast||WLP002||WYeast 1728||WLP001||WYeast 1728||WLP005||WLP001|
Now isn’t that interesting? Out of 12 examples, 6 of them are using the Chico strain. There are a few English yeasts, the Scottish yeast (personal fan), and the Bell’s proprietary strain, but half the recipes are sticking with Chico.
There are a few plausible reasons for this. The first is that Chico is cheap and easy to get a hold of, so when you need a big pitch for a RIS it is a go to. It’s also a fairly common house yeast, especially when you don’t want an expressive yeast dominating the beer. It’s clean, has good alcohol tolerance, and it pretty forgiving in my experience. All around a solid yeast, if a bit plain.
These results actually coincide with our Reddit RIS survey.
A vast majority of responders said that they use US-05, 1056, or WLP001 for their Imperial Stout. Reasons included being a clean yeast and being readily available. Responders who selected that they used US-05 specifically (a majority) noted that it was an easy way to ensure that they are pitching enough yeast.
When selecting a yeast for a RIS, there is an additional consideration beyond the yeast profile, which is alcohol tolerance. Most yeasts should be able to handle the lower end of the high gravity spectrum, somewhere in the range of 8% – 10%. As you increase the OG, those 8% – 10% yeasts will still ferment away until they reach their limit, leaving you with a sweeter, less alcoholic beer. As you plan your brew, ask yourself what you’d like the alcohol content to be, and how sweet you’d like the beer.
WYeast 1098 has an alcohol tolerance of roughly 10% ABV. So 10% and under, you’ll probably get your full attenuation just fine. Anything higher, and you might start to see a higher finishing gravity. On the other hand, WYeast 1728 has a tolerance of about 12%, which means in that same wort you’d get a bit more alcohol, less sweetness, and a lower finishing gravity.
When planning your RIS, you can use this to your advantage. Low ABV does not mean the RIS is worse. Start with your product and work backwards. If you want a 10% ABV Sweet RIS, go with something that won’t attenuate as much, or plan your malt bill accordingly. I point this out to make it clear that the malt bill is not your only tool in a flavor arsenal, your yeast is more than just the flavor profile.
As a side note, bottle conditioners should keep this alcohol tolerance in mind. If your yeast ferments to the point it can’t handle the alcohol tolerance, you may have issues with bottle conditioning since the yeast can’t ferment the additional sugar. Something to keep in mind.
In my RIS, I’m looking for something around 11% and a bit sweeter, but leaning roasty. I also have quite a bit of experience with both US-05 and WYeast 1728, and I know that 1728 leans a bit too sweet just because of the flavor profile, and with the extensive use of the Chico strain in our commercial examples (which may just be because it is a cheap, neutral house yeast), I’m happy to try it out. If your split-batch sense is tingling, you’ve been reading too much Brulosophy.
I know it doesn’t make sense chronologically in the brewing timeline to talk about fermentation right now, but since yeast and fermentation are so closely tied together I decided to talk about it in this section of the article.
The adage “Brewers make wort, yeast makes beer”, is a good rule of thumb for talking about the importance of yeast, but it also makes it seem like once yeast is pitched the brewer has no say in the matter, which absolutely isn’t true. There is still a lot to be done in this stage, including the pitching itself, temperature control, pH, o2, and so on. Don’t take your hands off the wheel once the brew day is over, we aren’t done yet.
As our gravity increases in the wort, so does osmotic pressure. Osmotic pressure is the force developed between yeast cells, and can affect the yeast health, in turn affecting fermentation. One way to combat this is by keeping a lower original gravity (around 1.100 is where you may want to max out). If you do want to make a bigger (14% +) beer, consider a staggered addition of wort, steadily adding more wort during fermentation so that the yeast can work in a better environment.
Pitch Enough Yeast
Osmotic pressure, higher gravity, more alcohol, typically a high percentage of adjuncts, usually lower pH because of the roasted grains (water portion coming soon!), RIS are not built to be the optimal environment for yeast. This is why it is important to make sure you are pitching enough yeast for the beer. For ales, the average recommended pitching rate is .75 million cells per mL per degree plato. That rule of thumb is about double for a lager. For a high gravity beer, around 8%, I like to use a hybrid pitching rate, which is 1 million cells per mL per degree plato. This helps take stress off of the yeast to combat those earlier issues we discussed, and also helps combat the risk of stuck fermentation.
In additional to the volume of yeast you pitch, always make sure that the yeast is vital. There is a serious of articles on Brulosophy about this concept, and I’m not smart enough to get into the technical side of why this is a thing. What I have noticed is that by making my viability starter (cell count) then doing a vitality starter, my time from pitch to high krausen has drastically diminished. It is a way to make sure you are pitching healthy yeast that is ready to go.
Shameless plug for an awesome yeast pitching calculator. Select Hybrid rate, love your life.
As gravity increases in the wort, oxygen solubility decreases. So our higher gravity wort needs more yeast, and that yeast needs more oxygen, and that oxygen is less soluble in the wort. Again, RIS is not necessarily on great terms with yeast. Some of the people at Brew Your Own recommend 12 – 13 parts per million Oxygen for big beers. For that range, you need pure o2 and a diffusion stone.
Personally, I’ve aerated with a diffusion stone and aerated via shaking. In theory, shaking shouldn’t get me above about 8 ppm oxygen, but I haven’t really noticed a difference in my beers. Both are fairly simple, and I find myself shaking more often than not just so I don’t need to sanitize more things (and buy more tanks). Try it for yourself, but either way you should be aerating.
Another method I’ve employed is oxygenating twice, once at pitching and then once again twelve hours in. Here is a quote that was pointed out to me by Derek Springer of Five Blades Brewing, from Yeast:
Generally, you do not want to add oxygen later, as it can disturb the delicate balance of flavor and aroma compound creation. One exception is when brewing very high-gravity, high-alcohol beers. In those cases, where the yeast need large reserves to ferment the beer to completion, a second addition of oxygen between 12 and 18 hours after pitching can make a tremendous difference in attenuating the beer to the desired level…For high-gravity beers, adding a second dose of oxygen between 12 and 18 hours can help fermentation speed and attenuation. The yeast quickly takes up this oxygen and uses it for cell membrane maintenance and the production of intermediary compounds. Research also indicates the addition of oxygen at 12 hours increases fermentation speed by 33 percent and decreases such as diacetyl and acetaldehyde. Why wait until 12 hours? You are waiting for the yeast to complete at least one cell division (pp 66-67, 83-84).
Again, try it for yourself! For me, I’ll be shaking twice to aerate.
For this section, I have a hard time making any recommendations. This is something that is so dependent on yeast strain and the commercial examples either weren’t available or weren’t very consistent. All I can say is that if you’re aerating twice and pitching a ton of vital yeast, your are going to have a lot of vigorous fermentation activity. Make sure you’re doing something to resist temperature swings, whether that is using a swamp cooler or using a fermentation chamber.
Based on the above information, I plan on fermenting around 64F with US-05. But I do have a few experiments born from this, and the list grows:
- Is there a difference between beers that are aerated with pure o2 versus shaken?
- What yeast do I prefer? Chico? WLP090? WYeast 1728?
Next time we will be talking about water chemistry and the mash!
Reddit Homebrewing, for their awesome survey participation
Bernot, Kate. “What makes a great imperial stout…and where can we find one?”. Draft. Jan 22, 2016. Retrieved from: http://draftmag.com/what-makes-a-great-imperial-stout/
BYO Staff. (2005). Keys to Aeration: Advanced Brewing. Brew Your Own. Retrieved from:http://byo.com/brown-ale/item/958-keys-to-aeration-advanced-brewing
BYO Staff. “Russian Imperial Stout: Tips from the Pros”. Brew Your Own. Dec., 2005. Retrieved from: http://byo.com/bock/item/1337-russian-imperial-stout-tips-from-the-pros
Daniels, Ray. Designing Great Beer.
American Homebrewers Association – Recipes
Past Parts of the Series