The Quest for the Top in the ABV race

There has been a very pronounced trend lately to see beers advertised with higher and higher ABV claims. I distinctly recall seeking out Dogfish Head’s World Wide Stout in my early days of beer geekery and being blown away by just how different this beer was from anything else I had had up to that point. It is pretty clear from looking at the Ratebeer Top 50 that high-octane beers are generally perceived to be excellent as illustrated by the 32 beers on this list that are 10% ABV or greater and 40 that are 9% ABV or greater. Further breakdowns show that the imperial stout style which is, by definition, high alcohol dominates this list with 27 of 50 from this one style alone. It seems a natural extension of this approach to take an imperial stout and see just how high you can get the ABV up and what kind of product will result from this. To this end, BrewDog of Scotland has launched their latest project, “Tactical Nuclear Penguin Imperial Stout”.

According to the brewery press release, this beer started out as a 10% ABV imperial stout that was then aged in two single malt scotch casks for a total of 16 months followed by an icing process to bring the ABV to a lab-verified 32%, surpassing the previous record holder, Schorschbräu Schorschbock 31%. This trend toward higher ABV brews has been going on for quite some time and I don’t think that will change anytime soon, but I would like to write a little bit about ways that brewers create high gravity beers, some studies that have been done on the effects of high gravity brewing on the final product and where there are knowledge gaps about the process.

Producing high-gravity beer

The classic method of producing a higher-ABV product is simply to add more fermentable material.  Most of the academic studies that have been done on high-gravity brewing is usually done by large brewing companies (or funded by them) and this is the technique that is most commonly used.  Often large brewers will ferment a high-gravity wort (1065-1080) in order to reduce the amount of fermenter space required to get a given amount of ethanol.  This high ABV beer is then blended with water in order to produce a larger volume of lower-gravity beer at a lower cost per unit of finished product.

This lowered cost per unit does not come free however.  Yeast are living organisms and as such they have evolved a number of responses to physiological stresses.  High gravity brewing imparts a stress known as osmotic shock in which the concentration of dissolved material (mainly sugars) in the growth medium is higher than is optimal for the yeast.  In order to respond to this, the yeast produces what are termed compatible osmoprotectants, that allow the cell to function under the higher gravity conditions.  As the gravity drops while fermentation proceeds, the majority of these compounds will be recycled within the yeast, but in response to the stress, the fermenting yeast can throw off a number of higher alcohols, acetaldehyde and esters in addition to the desired higher ABV.  In principle, these compounds aren’t harmful, but they do tend to lend the finished beer a distinctly “dirty” flavour profile.

It is worth noting however, that many of these studies on high-gravity brewing are typically done during lager fermentations, in which the desired product is a light-bodied, lightly hopped, fairly clean product with little in the way of either yeast or malt contributions.  In these backgrounds the contribution of low-levels of flavour products is substantially more noticeable than it might be in a product with more contributions from either malt or hops.

In fact though, the term “high-gravity” is a relative one and the ~1065-1080 that is used in the brewing of lager on an industrial scale is merely a starting point for a wide variety of styles within the craft beer industry.  It is fairly routine for worts used in doppelbocks, imperial IPA, barleywine or imperial stout often start around 1090 and some can be higher than 1150.  Brewers have found ways to encourage the vigorous fermentation of these types of worts by increasing the pitching rate (the amount of yeast added at the beginning of fermentation), by aerating at multiple points during the early stages of fermentation (to encourage more yeast growth during the initial phase of fermentation), by feeding the beer during mid-fermentation (to reduce the osmotic shock experienced by the yeast) and by using yeast strains that have been selected for higher ethanol tolerance (ethanol is quite toxic to yeast at high levels).  Some brewers have used each of these techniques, whether alone or in combination in order to produce their high-octane brews.  The strongest beers in the world however, generally make use of a process called “eising”.

What is “eising”

Eising is a process whereby the alcohol in a beer is concentrated when the beer is slowly lowered in temperature until ice starts to form.  The frozen portion of the mixture has a higher concentration of water ice than the bulk liquid does.  In principle, this means that the liquid portion now has a higher concentration of alcohol than the frozen portion does.  Many people have written to the effect that the alcohol won’t freeze because it has a lower freezing point than water and therefore ALL of it is left behind.  This is false and what actually happens is substantially more complicated than what is written elsewhere on beer websites or internet forums and I’m going to spend a few paragraphs trying to clarify the process.

For a given beer that will be eised, as the temperature drops the proportion that freezes will also have a higher alcohol concentration, but the concentration of the alcohol in the liquid portion will be higher still.  In thermodynamics, the description of the relationship between the relative concentration of each component in a mixture during either cryo-concentration or distillation can be represented by a phase diagram.  Without getting overly technical, a phase diagram shows the concentration of each component in a mixture as a function of temperature.  In practice, these diagrams are very complicated and they can be dramatically affected by the presence of other compounds in the mixture, which means that there is absolutely no information about phase behaviour of actual beer during a cryocencentration.  However, there is information about how pure ethanol-water mixtures behave under these conditions.

K. Takaizumi and T. Wakabayashi, Journal of Solution Chemistry

In the attached figure, the only information that is really relevant to the discussion of brewing is the filled black circles in the upper left hand portion of the graph.  This shows the composition of the mixture as a function of temperature.  The mixture composition (X EtOH) is expressed as mole fraction, which is a more useful measure of concentration for chemists than either ABV or ABW.  A mole fraction of 0.05 is ~15.1% ABV, 0.10 is ~28.0% ABV and 0.15 is ~39.4.  This graph shows that even a very small level of mole fraction concentration can be a very significant in terms of ABV.  In reality however, the presence of both unfermented sugar and the ethanol from fermentation depresses the freezing point significantly, such that a finished beer (like that used for making eisbock) won’t begin to freeze until the temperature is around -5 to -8 degrees.  This makes it necessary to reduce the temperature even more in order to begin to get freezing and therefore ethanol concentration.

The eising process also has the effect of concentrating any residual sugars that are present in the initial beer.  If one were to taste the ice that is removed it would be a slightly sweet, slightly alcoholic mixture, likely with some of the malt character as well, but that would be much reduced compared to either the initial beer used or to the liquid fraction of the beer/ice mixture.

Isn’t that dangerous?

There have been several reports, usually anecdotal about toxicity associated with drinking distilled products and the argument has been made that this could be extended to eised products.  I’ve done a little bit of research on this topic and in general there is very little reason to be concerned.  One study suggests that the death associated with methanol toxicity from drinking is usually accidental from either mistakenly or intentionally drinking methanol.  In addition a study of confiscated illicitly produced moonshine showed that only a single sample out of 48 contained any methanol at all, and even that sample had an amount well below what is considered toxic.

But is it any good?

I’ll conclude by stating that brewers have always tried to push the envelope.  Whether in the desire to create hoppier version of the IPA in the early-mid 1990s, thereby leading to the IIPA craze or in the desire to create stronger versions of stout for export to the Russian tsars in the 18th century, or in the creation of stronger versions of doppelbocks by the method described above, brewers are always looking to see how they can create new flavour profiles that actually taste good.  Many of these experiments are banished to the dustbin of history (please, someone send Cave Creek Chili Beer there) but some go on to enjoy widespread popularity and success.  Having tasted only a few of these very high alcohol beers (DFH WWS and Sam Adams Utopias come to mind), I can say that they are very unique and when well made very delicious.  It’s a big, wide world here in the craft beer community and we should be encouraging of brewers who push the boundaries (even when said brewers push them too far) to provide us with new, delicious products.  As long as the product in the glass tastes good and can be shared with friends, that should be the only criterion on which it is judged.

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