Have you ever poured a beer or been drinking from a bottle when you noticed a thin film of white stuff in the bottom of the bottle? There are some odd theories floating around about that stuff. Here is what is really is.
Beer lovers who are paying attention will sometimes notice a thin, white film in the bottom of their beer bottles. This happens most often with wheat beers which, I suppose, led some of them to assume that it is wheat added to the beer “for flavor.” I have heard that explanation more than once.
It is not wheat. It is dead or dormant yeast cells and they are supposed to be there. In the case of some wheat styles, they do indeed enhance the flavor, however, that is just a happy side-effect of their real purpose.
There are two ways to carbonate beer. The first is via a method called forced carbonation. This is where a measured amount of CO2 is pumped into a sealed container full of cold, flat beer. More gas than can actually fit in the container is pumped in creating pressure. Overtime, the beer will absorb the gas and become carbonated. This is how beer and other carbonated beverages continue to fix even after the initial release of pressure when their containers are opened.
The other way to carbonate beer, called natural fermentation, is to add a small amount of sugar to the beer before packaging it. In this case, the yeast that remains suspended will eat the sugar, fermenting it into alcohol and CO2.
The amount of alcohol produced during this secondary fermentation is negligible but, the CO2 will be just enough to carbonate the beer. Just like in the forced carbonation method, the CO2 produced is more than the container – bottle, in this case – can hold so the beer is forced to absorb it. As the sugar is being fermented, the yeast is also reproducing then dying or going dormant and drifting to the bottom of the bottle, creating the white film.
In most cases, the yeast cells have very little effect on the flavor of the beer. They will make the beer appear cloudier if poured in a clear glass but, that is about it. In the wheat beer styles that I mentioned above, the yeast does enhance the flavor of the beer, usually making it a bit spicer, if it is mixed in with the beer as it is being poured. A popular example of this is hefeweizen.
So, the stuff in the bottom of your beer bottle is harmless, it is meant to be there and it might just make your beer a little tastier.