Science on Tap: Temperature

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Science on Tap: Effects of Temperature on Beer Aging
Follow link to Part 1: Science on Tap: Into the the Science of Beer Aging
Follow link to Part 2: Science of Tap: Styles meant for Aging
Over the course of the last two installments of Science on Tap, we have discussed, in general, the practice of long-term aging of beer (or cellaring), and why particular styles of beer are best suited for aging. There are many reactions occurring in your beer during aging, and storage temperature is the major driver of the rate for most of these reactions. Indeed, in commercial tasting panels, storage temperature had the greatest impact on flavor deterioration, haze, and color of the beer. The changes associated with high-temperature storage can occur quickly, and can be encountered often, at both the commercial scale, and the homebrew scale.

Summary of taste panel results after standard storage temperature (Number 1) versus warm storage temperature (Number 2)
Storage temperatures are important to beer flavor. Beer contains a variety of compounds that are capable of autoxidation if temperatures get too high. This means that a beer that spent two weeks at 100F will have a similar loss of freshness as a beer that spent three months at 70F. Again, remember that loss of freshness can be good or bad, depending on the beer style, and the goal for the aging of the beer. The recommended temperature for long-term aging of beer is 55F. I think of that as an upper limit. Below that temperature, the reactions will still occur, albeit at a slower rate. Above 55F, the reactions will occur at such a speed that the beer ages perhaps inappropriately. A useful generalization when thinking about this concept comes from Swedish chemist Svante Arrhenius, who determined that the reaction rate doubles for most common chemical reactions for every 10C increase in temperature, for low-energy barrier reactions. High-energy barrier reactions occur 8 times faster. Basically, some aging reactions in your beer are occurring twice as fast at 73F, compared to 55F, and some are occurring 448 times faster. Of course, many other variables are at play here: the rate of reactions does not always increase proportional to the temperature increase. Now, think of imported beer that has been in a shipping container for weeks, or your imperial stout that hits 80F in the summers. A few weeks, or even a few days, at these high temperatures could make a one month old beer taste like it has been aged for a year, which is rarely a good thing. Moreover, increased temperature promotes the growth of beer spoilage organisms, if present.

Comparison of loss of freshness during storage of beer at various temperatures
Additionally, high temperatures may encourage chemical reactions that are absent, or rare, at normal cellar temperatures, resulting in an inappropriately-aged flavor profile, as opposed to an expected aged flavor profile. The impact of these changes depend on your ability to taste them, the flavor thresholds of the compounds, and the overall character of the beer. A forced-aging test is an experiment that is really worth trying out at home (which I mentioned in one of the other installments): take two bottles of the same beer, a homebrew or commercial brew, put one in the fridge, and put the other in a warm area. I put mine in the oven on the lowest setting (mine goes down to 170F) for a few hours. After the beer is stored warm for a period of time, open both bottles and compare the flavor differences. You may be able to force-age your beer at 90F, instead of keeping it at 55F for a length of time. But, be advised: the window at which the flavor will be balanced and appropriate will be very small. Remember the rate of reactions, as mentioned previously. At excessively high temperatures, some aging, oxidative, and/or staling reactions are occurring staggeringly fast, whereas these reactions may not occur at all when the beer is aged at an appropriate cellar temperature.
How does an increase in temperature influence the flavor? In general, the same set, or type, of reactions will occur over a shorter time frame. Recall the Dalgliesh chart from part 1 that describes the general change in the flavor profile of the beer over time. You must compress the graph, then extrapolate (or extend) the lines. However, the dynamics of the changes are influenced by the style of the beer, among other things. For example, the sweet taste described in the chart is not a single reaction, but a large group of reactions that can occur, both, simultaneously, and sequentially. That bottle that has been sitting on top of your fridge (a notoriously bad place to cellar beer) has been subjected to heat, not to mention light and vibrations. Imagine, then, how this environment will influence the chart.
*Potential or theoretical flavor changes in beer, over extended aging by extrapolating curves
*Keep in mind that this is a generalization. The dynamics of the changes occurring in your beer may not always simulate this chart.
But what about temperature cycling during storage? Does cycling your beer between warm and cool do more damage than just warm temperatures? This topic has been debated pretty extensively. The Master Brewers Association of America says that deterioration of beer flavor only occurs at high temperatures. The high temperature drives the reactions, but the low temperature slows the reactions. The time spent warm causes the damage to the beer, and not the act of cycling through temperatures. The greatest impact of temperature cycling is in the clarity of your beer: cycling can turn temporary chill haze into permanent haze.

Chart showing the impact of temperature on beer flavor. Note the rate of flavor deterioration relative to temperature
This article comes with the usual caveat: semantics. Descriptors such as flavor deterioration, damage, and, aged can not only be subjective, but relative to the goal of your beer as well. The flavors in a Russian Imperial Stout may technically have deteriorated during long-term aging, but those deteriorated flavors are what give an aged RIS its characteristic profile. Heat is punishing to your beer. Increased temperatures drive oxidation reactions and encourage the growth of spoilage organisms. Once your fermentation is complete, freshness and stability of your beer is best preserved by storing it as cold as possible, but any warmer than that, and you're likely looking at some unexpected off-flavors.
 
Check out my other article describing the effects of age on different styles: https://www.homebrewtalk.com/the-science-of-beer-aging-styles.html
The link is also at the top of this page.
 
@DrVertebrae try Founders Breakfast Stout or The Abyss from Deschutes...to name two. The magazine All About Beer's January 2015 issue is devoted to beer aging too.
 
@ColoHox great article and very informative, as are the other articles in your series. This must be why my 8.1% ABV Wee Heavy tastes so much better after aging 10 months at 40F.
 
this was great, iv been very interested in sherry and rum flavours i get in beers like fullers 1845 and northcoast strong ale, its very hard to find any info on this so this was a nice article to read
 
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