Tuesday, March 6, 2012

Graphically Evaluating Yeast Character

Of all the aspects of homebrewing there are to take an interest in, I have always found "yeast" to be among my favorites. Not necessarily how yeast replicate - I don't possess the upper level science skills for that - but rather how individual yeast strains can give beer such a variety of flavors and characteristics. While it is safe to say that most homebrewers stick to using just one or two yeast strains for the majority of their brews, I find great pleasure in trying as many strains as possible. With that in mind, I don't even want to know the amount of money I've spent trying and re-trying different yeast strains for the past five years.

Regardless, one of the problems when talking about yeast is the lack of useful information about the different strains and flavors that yeast can give a beer. While there is no shortage of information about the different types of hops and specialty grains used in brewing, most of the time you will only find a tidbit or two about how yeast "X" either did a good or bad job, with few details on the individual character. I want to know all the details; How yeast flavor changes with pitch rate, temperature, oxygen levels, how one strain compares to another, and the types of ingredients it goes well with. Furthermore, as we all know taste is highly subjective, wouldn't it be more useful to state the individual flavor elements of a particular strain, instead of saying whether or not it made a good beer? Let's see those tasting notes!

In an attempt to provide a visual method for comparing yeast strains, I've come up with a few spider graphs to illustrate the basic fermentation characteristics of my favorite English yeasts. Spider graphs have been used by breweries to describe beer flavor and by hop growers to show the different characteristics of their hop varieties. It is my hope that something like this could make it easier for new brewers to compare yeasts and/or choose a strain that would best suit the beer they are interested in brewing.

If you were wondering how I came up with these numbers, I went through my old brew logs and much of the manufacturer data to form an "average" for each of the points I plotted. While most of the data is self explanatory, 'bottle stability' and 'malt integrity' intend to represent how stable the yeast is in the bottle (is it prone to reactivating beyond the F.G) and how well the original malt character holds up to the yeast flavors. Same is true for hops and bitterness. Also while fermentation has a greater impact on ester production (temp/pitch) than yeast strain alone, I hoped to at least show the intensity of esters that each yeast produces in a relatively standard fermentation process.


Lastly, could this method be an effective way of comparing yeast derived flavors? Would you like to see something like this next to the yeasts in your LHBS? Regardless, I hope to write more about individual strains in the future and possibly use spider graphs to illustrate the results of some of my experiments. And please excuse my total lack of graphing skills...

7 comments:

  1. Excellent post Will, I look forward to more of your analysis regarding yeast. What would be interesting is how these spider graphs breakdown by style of beer.

    I still think I'm suffering from "bottle stability" when conditioning with these yeasts, most recently using 1469. 1882 too has been fine in the keg but not in the bottle. All this has me wanting to do split wort fermentations but managing all the strains is a mental mountain I need to get over and just go for it, or settle in on one and put it through the grinder.

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  2. Great stuff man. I too am a yeast addict and thus try to split just about every batch I brew. I have yet to to English yeasts side by side (usually doing English vs. Belgians for greater diversity), but I have resolved to both try similar yeasts side by side as well as begin posting my tasting notes of split batches in the same post.

    I love the spider graphs. I got into them when I was working in the coffee field. They are super helpful, especially over time.

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  3. I am very interested in bottle stability since I am not set up for kegs yet. Any other strains that do well in that category?

    Will--I know you will be interested to know that Ron Pattinson will be in Boston next Wednesday, 3/14 for the newest Pretty Things Once Upon a Time beer release with two versions of the Barclay Perkins X ale--1838 and 1945. www.oldbeers.com

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    1. While I would defer to will about his understanding of the variability of bottle stability with a yeast, listening to respected people in the field like Dr Bamforth highlight that the variable that affects flavor stability more than anything else is storage temperature, by far.

      According to Dr Bamforth, chemical/flavor reactions and changes (flavor de-stabilizing) happen 2-3x as fast every time you go up 10 degrees C. If the flavor of a bottled beer is now no longer as pleasing after 3 months, and you stored it at 20C/68F, by comparison, if you had stored it at 10C/50F you'd had gotten 6-9 months out of it before you got the same flavor changes. At 0C/32C you'd have gotten 1-3 years out of it, all else being equal. And if you had it at 30C, the flavor diminishing you were displeased with would have happened within 4-6 weeks.

      The dormant/dying/autolyzing yeast in the bottle of a bottle-conditioned beer are going to break down that much slower the colder and more temp-stable they are stored no matter what yeast is used.

      That said, while I wouldn't expect too much from a 4% bottle condition beer fermented on hefeweisen yeast after 2 years even if it were stored at 0 degrees C, I'd probably still drink it!

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  4. It would be amazing if someone homebrew shops could offer a 'tasters' like brew pubs might - small samplings of a simple wort fermented under optimal conditions etc...I'd pay for that privilege, as compared to buying and tossing said mysterious yeast into a batch of wort that I put so much effort into, only for it to turn out 'meh' because that yeast strain was not my cup of tea.

    If Wyeast and White Labs can ship live yeast in packs and vials, I'm sure they could ship little tasters of sampler wort from yeast x, etc. It'd surely be worth a few bucks and maybe make the end user that much more satisfied with their beer and the product choice they made.

    Overall the sense that a yeast strain often defines the taste of a batch of beer, and at times it completely overwhelms the finer details of the beers recipe is too often downplayed. The gravitation toward using Chico yeast makes sense, in that it comes as close to eliminating the yeast variable and risk as much as possible within reasonable homebrew (ale temps, some flocculation) parameters.

    No matter what more has to be done in this area, and your approach is not insignificant.

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  5. I actually first saw these types of graphs when buying coffee beans, they were really quite helpful. I've made up a few more yeast graphs, though I'd like to go back and do one graph for yeast fermentation characteristics and another for the flavor profiles.

    Bottle stability is a weird thing. Some strains are notorious offenders, like 1968, whereas other ones can turn out fine or not. A good rule of thumb is that those yeasts that are fast flocculators but not highly attenuating strains, can give problems in the bottle. 1968, 1318, 1882, and 1469 have all given me problems in the past. Strains like 1090, 99, bedford bitter, 1335, 1768, and the cleaner, minerally ones have generally been pretty stable.

    I'd love to make the trip to Boston for the pretty things release, but alas, I am broke. Hopefully a few bottles make their way up my way. I tried their India Porter and it was really nice.

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  6. I worked in a cafe chain for ~4 years, and a similar kind of (subjective) flavor analysis was used to compare one beans region+roast characteristics to another.

    To say a coffee is 'lemony' or 'earthy' is to say nothing in itself. Within a write up, these words are black or white descriptors to the brain. Customers would often be underwhelmed by the brief write-ups and say, 'this doesn't taste like lemons, it tastes like coffee!'

    However, to put coffee A as a '1' on the citrus scale, next to coffee B as a '5' on the citrus scale' next to coffee C as an '8' on the citrus scale, and so on and so forth along side each beans other other characteristics helps a lot more in describing flavors, when done in conjunction with a few tastings as reference points; i.e., "I know I tried coffee B and liked it, but wouldn't mind something a little more citrusy, so I'll try coffee C even though it is less roasty, etc." However, to someone who has never tasted two analyzed coffees and then looked at the graphs, there is no reference point. Then, despite the abundance of information, all descriptions are moot. That too is an essential component.

    "Brewing Classic Styles" has a 'wheel' diagram for hops that I find completely befuddling (page 20 on my copy). In this diagram, the names of dozens of hops are scattered around within a circle, which is surrounded by 7 flavor characteristics encompassing the circle's perimeter; some hop's names are in the center of the circle (what does that even mean?), while others are closer to the perimeter toward one characteristics like 'spicy.' Others will be halfway between the center and the perimeter of the circle, and/or straddling two characteristics, and with a letter like H after them to signify that they are 'also herbal.' I've found it more misleading than helpful.

    Whole not all of us appreciate the semi-scientific analysis of flavor, many of us homebrewers ARE geeks about it. With hops (and even malts), your spider graphs would be a vast improvement over the typical 'descriptive phrase + common substitution' charts.

    As for yeast strains, they are excellent graphs, and the only missing element may be a way to taste even two identical worts fermented with two different yeast strains which have been analyzed for a starting reference point.

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