Wednesday, December 18, 2013

Careful Cellaring, Part 2: The Importance of Temperature

Cellaring beer properly means paying close attention to the many elements that can make your collection age for the worse. One of the most influential factors that can cause any good beer to go bad is temperature. To best understand how temperature effects beer we've once again turned to Jess, our Quality Specialist, to explain what happens to a living beer when it spends time at less than ideal temperatures.


Why do you keep your milk or yogurt in the fridge? For some of the same reasons you would want to keep a beer in the fridge: it helps keep the beer as fresh as possible.

Too Darn Cold

Cold storage is not to be confused with frozen storage. Besides possibly making a beer-bomb in your freezer, keeping beer at sub-zero temperatures is not preferable. There actually are a few instances where freezing temperatures are used in the brewery:
One method, called ice stabilization, is sometimes used to help with filtration by causing the precipitation of proteins and phenols in a beer. Historically, (and recently, in the case of BrewDog) freezing a beer has also been used to “distill” beer to a higher alcohol. However, your average finished craft beer should never be frozen.



In craft beers that are not filtered and bottle conditioned, like ours at The Bruery, there are residual yeast intentionally present. In the event of a beer being frozen this can cause what is called “yeast bite”. When a cell is frozen it undergoes a lot of osmotic stress either from rupture due to this stress, or through the formation of ice crystals. This essentially leaves a lot of dead yeast cells floating around and will often create meaty off-flavors (yuck).

On the chemistry side of things, freezing a beer will cause the precipitation of proteins and phenols creating an excessive amount of haze. Often people mistake haze for bacterial contamination. If the freezing is severe, the haze will become permanent and appear chunky. It won’t hurt you, but is not very appealing when pouring your beer into a glass.

In addition, freezing a beer can cause gushing. This is also another symptom attributed to bacterial contamination, but is not always the cause. Ice crystals act as nucleation sites for carbon dioxide to escape, therefore causing extreme foaming. There are many other reasons for gushing (i.e. overcarbonation, the presence of wild yeast, contamination), but that is a whole different article.


Too Darn Hot

The most damaging threat to beer is keeping it at or above ambient temperatures, as this accelerates oxidation. There is a lot of complicated chemistry that goes on during oxidation. Some basic mechanisms include auto-oxidation, where molecular oxygen acts directly to produce an oxidized compound and then there is its polar opposite called oxidation without molecular oxygen. Oxidation without molecular oxygen involves an electron transfer where the oxidized compound is reduced. One graph that I think really illustrates the idea that oxidation/staling increases exponentially with temperature is below (Bamforth, 2004).



Essentially this graph is telling us that it can only take one day to ruin a beer if stored improperly. As with most chemical reactions they are sped up by temperature and this is described by something called the Arrhenius Law:

kt+10 = 2῀3kt

Where kt = the rate of a chemical reaction at a given temperature, and kt+10 = the rate of that reaction when the temperature is raised by 10 °C. So when you increase the temperature you increase the rate of the reaction.

Another great graphical representation is shown in the chart below. It is a graph of sensory changes of beer flavor over time (Dalgliesh, 1977). As time passes, the aspects in the graph either decrease or increase. If you consider temperature, these flavor constituents will change even faster. In some cases the resulting flavors are desired as they will mellow a beer that may be slightly intense. However, keep in mind this can only happen at appropriate cellaring conditions. In the case of hoppy beers, these are best consumed fresh as bitterness decreases linearly over time.



Essentially, the best way to protect a beer is to store it at the appropriate temperatures. Whether you are going to consume the beer soon or keep it for cellaring, the best thing to do is to treat it like you would the milk in your fridge.

In the brewery, the brewers have the power to reduce the impact of temperature by keeping dissolved oxygen to a minimum and allowing some healthy yeast to be present in the final product. But once it is in the hands of the distributor and the customer there is nothing that the brewer can do to prevent the damaging effects of poor temperature storage.





Post written by Jessica Davis, our Quality Specialist who makes sure our beer & yeast are healthy. Jess has worked in many a lab, including the one at Stone Brewing Co.

Read more of our cellaring series:

3 comments:

d rat said...

Awesome blog Jess. We miss you here at Stone Brewing Co.

Leo Nomoto said...

Awesome post!

What are your thoughts on cellaring beers in a fridge?I know it will take a whole lot longer for ideal aging beers to age but do you see anything negative about cellaring beers in the fridge? Some say the fridge is too cold and dry which can lead to oxidization problems due to corks and caps "wearing out."

Also do you have easy tips on when to store upright and when to lay down?

Thanks!

Cambria said...

Hey Leo,

Refrigerators can be very drying in general, but keeping a consistent, cool temperature is most important above all. Sours can age on the side, but for non-sours, storing upright and limiting the surface area that is in contact with airspace in the bottle is best. Cheers!