Thursday, July 31, 2014

Bottle Conditioned Beer

Few average beer drinkers are aware of the variety of packaging options--bottles, casks, growlers, filtration, bottle conditioning, pasteurization, krausening, etc.--and how these affect the product they receive.  In particular, bottle conditioned beers are very common and require special storage, handling, and serving practices to ensure the beer is delivered as expected.  They contain live yeast which are fed a measured amount of simple sugar to naturally produce carbonation before settling to the bottom of the bottle.  Bottles must be stored upright in a cool dark place--optimally around 50F--to prevent lightstrike, oxidation, and to let the yeast settle.  Before serving, the beer should be chilled to an appropriate serving temperature for at least 24 hrs to equalize the partial pressure of carbon dioxide, then poured into a clean glass, leaving the yeast sediment behind.  The dormant yeast is not harmful, but is not an expected part of the flavor profile for most beer styles.  Many of the finest beers in the world are bottle conditioned, but improper handling can ruin the beer.

Everybody knows the difference between a keg and a can, but besides beer geeks, few are aware of the variety of packaging options--bottles, casks, growlers, filtration, bottle conditioning, pasteurization, krausening, etc.--and how these affect the product they receive.  The packaging is intimately tied with the optimal storage and handling practices as well as serving conditions, and knowing how to treat a beer at each step can make or break a beer.

I don't have the time or space to cover everything--there are entire courses and books about the subject--but I do want to talk specifically about bottle conditioned beer and what makes it different from a can of Bud Light.  After all, this is the method I use for bottling my beers; if you're drinking one, I hope you're enjoying it in the best possible light.

Bottles vs. Cans
There's been a lot of discussion in brewing world lately over the difference between bottles and cans, as more craft breweries switch to cans.  Cans offer a number of advantages for commercial brewers: cheaper, thinner, lighter, more durable, better thermal conductivity (chills faster), tighter seal, lightproof, and product differentiation.  As a consumer, the most important difference to be aware of is that bottled beer is susceptible to lightstrike, also known as "skunking."  Light--especially the higher energy end of the spectrum where you'll find UV, blue, and green--causes the iso-α-acids (which give hoppy beers their bitterness) to break down into the same sulfur-based compound that gives skunk spray its offensive odor.  Brown bottles filter out most of this shorter wave-length light, protecting the beer better than green or clear glass, but you won't want to leave any bottle out in the sun all afternoon.  When treated properly, cans and bottles will deliver the same product, package-conditioned or otherwise, so it's primarily a question of convenience and marketing.

Bottle Conditioning
But what defines bottle (or can) conditioning?  Well when a beer is fermented, most of the yeast settles to the the bottom of the fermenter and goes dormant after it finishes its work.  However, a small percentage remains in suspension.  If the beer is then packaged with a small amount of simple sugar, this yeast will awaken and ferment the sugar, producing a small amount of alcohol and carbon dioxide.  The alcohol and flavor compounds produced will be insignificant compared to those produced during primary fermentation, but in a sealed package, the carbon dioxide provides natural carbonation.  The amount of sugar directly influences the amount of carbonation, allowing brewers to produce both smooth English ales as well as the effervescent Belgian products.

This is the traditional way of doing it, but what are the alternatives?  Well many brewers force carbonate in a holding tank before bottling instead of adding sugar, some filter out the yeast and other haze-inducing elements prior to carbonation, some pasteurize the yeast to get a more stable product, and others reintroduce a yeast (the same or a different strain) specifically for carbonation and conditioning.  There are advantages and disadvantages to each method, and the form of packaging often reflects the brewery's position vis-à-vis tradition, flavor, logistics, and budget.

In case you missed it, let me reiterate an important point: bottle conditioned beer contains live yeast.  This certainly is not harmful (even beneficial if you believe this interview with Jim Koch), but it means that the beer in your fridge is essentially a living thing and will continue to mature over time.  While they are not actively fermenting, yeast can continue to break down other fermentation byproducts and off flavors (such as harsh fusel alcohols) that made it into the finished beer.  Some styles benefit from aging--particularly strong beers like imperial stout or barleywine--as these undesirable flavors diminish or as other flavors creep to the forefront.  However, lighter styles (both in color and alcohol content) usually deteriorate as hop flavors fade and oxidation stales the malt.

There general advice for storing beer applies equally to all beers, but there are a few practical points that are especially important for bottle-conditioned beers:
  • Avoid extreme temperatures:  High temperatures accelerate oxidation in all beers, causing staling.  This is less of a threat in bottle-conditioned beers as the yeast scavenge oxygen during the refermentation, but will still happen eventually.  High temperatures also accelerate yeast metabolic processes.  This speeds yeast ageing and can lead to autolysis, or rupturing of the yeast cells, releasing unwanted flavors into the beer.  On the other hand, dropping the beer below freezing will also cause autolysis and risks rupturing the bottle.  The sweet spot is around 50-55F for long term storage, but a refrigerator works perfectly fine for your everyday beer.
  • Store upright:  Unlike wine, beer is best stored upright to minimize exposure to any oxygen in the headspace.  In bottle conditioned beer in particular, the yeast will settle to the bottom of the bottle.  If you're careful not to agitate the bottle, you can pour off the beer at serving and leave the yeast behind.
  • Drink it:  If you don't have a specific reason to cellar a beer, it's probably best to just drink your beer.  Some styles hold up better over time than others, but most pale styles like IPA, wheats, and pilsner are best before you even get your hands on them.

When you're finally ready to drink your beer, the first step is to get the beer to serving temperature.  This isn't as simple as throwing the beer in the freezer for 10 minutes and dumping it in a red Solo cup.  First of all, temperature has a big influence on both how the flavors are presented and how we perceive them.  Cooler beer releases fewer of the volatile aromatic compounds detected by the olfactory receptors in the tongue and mouth.  In addition, cooler temperatures on the tongue decrease sensitivity to both sweetness and bitterness.  There are plenty of resources online to help guide you in choosing an appropriate serving temperature for your beer, so I won't go into that here.

But temperature plays an important role even before the beer is served.  The carbon dioxide that forms carbonation is more soluble in beer at colder temperatures, and slowly diffuses back and forth between the beer and the headspace as it warms and cools.  It can take up to 24 hrs for a beer to reach equilibrium after being placed in the refrigerator, so allow your beer a day or two to sit at serving temperature (or refrigerator temperature is usually close enough for most beers) before serving.  Not only does this ensure the proper carbonation level, but allows the yeast to settle out, reducing the risk of gushers and producing a finer, denser head.

The same goes for glassware: the shape of the glass can affect appearance, carbonation, head retention, and aroma, and there are plenty of people online who will tell you exactly what you have to use and why.  Some of it is tradition, as in the case of Belgians where every beer has its own glass, but there is certainly a noticeable difference between drinking a beer in say a goblet and a pilsner glass.

But again, before the beer is even poured, the glass must be painstakingly prepared to receive the sacred elixir in an ancient ritual predating the Belgian abbeys known as "cleaning."  Seriously, cleaning is a big deal.  They say that cleaning is 90% of brewing (the other half is fermentation), and it doesn't end when the beer is packaged.  Anything clinging to the glass--besides being disgusting--provides nucleation sites for the carbon dioxide to come out of solution, and any lipids--from milk, fats, soaps etc.--will bind to head-forming proteins and kill the foam.  Most people just drop all their glassware in the dishwasher which effectively clears debris, but leaves detergent residue which is just as problematic.  Immediately before using a glass, I always a give it a hot water rinse to remove detergent residue followed by a cold water rinse to bring it down to serving temperature.

Last but not least, I want to reiterate the single biggest (and easiest) thing to remember when pouring a bottle conditioned beer: there's yeast at the bottom!  Don't dump it in unless you want to drink it.  Yeast adds a thick haze and potentially even floating chunks of yeast which, although most obvious visually, also lend a creamy/spicy yeast flavor that for most beers is not an intended part of the finished product. For some styles--namely American and German hefeweizens--that's expected, but those are exceptions.  In general, it is best practice to gently decant the majority of the beer off the yeast, leaving the last inch or so in the bottle.  As mentioned earlier, there's nothing wrong with consuming yeast, so don't let the dregs (this is where the term comes from) go to waste.

If this seems like a lot to remember, realize that most of these practices apply to any beer: store upright in a cool dark place, chill for at least 24 hrs before serving, and serve at a style-appropriate temperature.  Then focus on the steps that are unique to bottle conditioned beer: letting it sit undisturbed to settle yeast to the bottom, and gently pouring the beer off the yeast into a clean glass.  If handled properly, bottle conditioned beer presents a unique drinking experience, and--particularly in stronger beers like imperial stouts, barleywines, and quadruples--can continue to evolve and improve with time.  Many of the finest beers in the world are bottle conditioned, but even Westvleteren XII can be ruined by inattention.

Further Reading:
Beer Magazine: History of Beer Packaging & Looking Forward
Martyn Cornell: A Short History of Modern Beer
Martyn Cornell: Bottle-ageing Beers
BYO: The Do's and Don'ts of Cleaning Beer Glasses

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