We all know that there's yeast in our beer, but some drinkers get squeamish when they find it lurking at the bottom of a bottle. It can look kind of gunky, so they assume it's not supposed to be there, or even that it might be bad for them. This isn't the case. It's not a fault. It's just a sign that the beer has been bottle-conditioned.
What Is Bottle Conditioning?
Bottle conditioning is when beer undergoes a second period of fermentation, this time inside the bottle from which it will eventually be served, in order to make it sparkling.
Homebrewers often use a simple form of the technique. At bottling time, the brewer will add a little extra sugar to wake up living yeast still present in the beer. This priming sugar restarts fermentation just enough for the yeast to naturally carbonate the beer and bring it into condition.
Commercial brewers use this technique, too. And although the basic idea is the same, they go about it in a different way. Any brewer worth his or her salt cares about yeast and worries about it getting stressed. Not because they think of it as a cute pet (well, maybe some of them do) but because they know that stressed yeast means bad beer.
The yeast present in the beer has already performed its initial fermentation. Now it lies there exhausted, drunk on its own alcohol, and generally not in great shape to square up for round two. So commercial brewers will add fresh yeast to do the remaining work.
Most agree that Champagne yeast is the best for the job. This wine yeast, also called Prise de Mousse (nerd name: EC-1118 Saccharomyces bayanus), is a very competitive strain that will inhibit other wild yeasts. This promotes clean fermentation and a finished beer free from any faults.
What Are the Pitfalls?
Whenever beer moves from one vessel to another there's cleaning involved. Brewers, more often than not, are scrubbers much of the time. With bottle conditioning, it's no different. Brewers risk ending up with infected beer if their bottles are not as clean as a newborn's conscience.
And then there's the pressure. Most homebrewers will have stories to share about bottle bombs. One of the biggest problems, at this level anyway, is adding the wrong amount of priming sugar. If you add too much, the fermentation will run wild, excessive carbon dioxide will build up in the beer, and boom: You've got a gusher on your hands—or worse. Too little sugar can be just as bad. You risk flat beer, sure. But you also risk a beer that's slick and buttery. This is caused by diacetyl, a byproduct of incomplete fermentation.
Why Do Brewers Use Bottle Conditioning?
The brewers behind Belgium's Duvel brand use bottle conditioning to produce a beer that contains almost twice as much carbon dioxide as most others. This creates so much pressure inside the bottle that they even invented a unique design to cope. The sturdy, stumpy brown glass bottles have become iconic. But why go to all this trouble?
"The high carbonation gives Duvel a beautiful roundness in the mouth," explains Natalya Watson, marketing manager at Duvel Moortgat. "It keeps the body light and gives Duvel its iconic look—a rich white head with fine bubbles."
Duvel is not alone here. The condition of beers produced in this way—that is, their carbonation, head retention, and general mouthfeel—is finer than can be accomplished using other methods. Bottle conditioning can also result in more complex flavors and give beers a longer shelf life. Done well, bottle-conditioned beer is The Good Stuff. It's worth seeking out.
Drinkers will always fret over whether or not to tip the yeast into their glass. In the end there's no reason not to. It's just down to personal preference. Some people find that adding the yeast gives a fuller, rounder flavor and smoother mouthfeel. Next time you drink a bottle-conditioned beer, go ahead—Swirl the yeast up with that last drop of beer and pour it in. You might like it.
Classic Bottle-Conditioned Beers
Bottle conditioning developed in the brewing traditions of Belgium, England, and Germany.
Belgium produces plenty of classic examples of bottle-conditioned beers. As well as Duvel, there are the lambic beers and blends such as those from Cantillon. Look in particular for bottles labelled “Oude Gueuze.” These are the ones produced according to the traditional methods.
If you fancy a German beer, look for bottled-conditioned hefeweizens. The Paulaner wheat beer is a great one. The term “Naturtrüb” is your signpost to yeasty goodness.
Brewers in England have long used this technique for all manner of ales. Fullers 1845 and Vintage Ale will see you right.