Have you ever poured a beer or drunk from a bottle and noticed a cloudy layer of white substance at the bottom? There are various strange theories circulating about that substance, but most of them are untrue. Here is the real explanation.
Yeast, Not Wheat
You may have observed that the mysterious cloudy layer appears most frequently in wheat beers, leading to some theories that the material is wheat added to the beer for flavor. In reality, it is not wheat; it is dead or dormant yeast cells, and they are supposed to be there. In certain styles of wheat beer, these yeast cells do indeed enhance the flavor, but that is just a pleasant side effect of their actual purpose: carbonation.
Carbonation—Forced and Natural
There are two methods of carbonating beer. The first method is forced carbonation. This involves pumping a measured amount of carbon dioxide gas, or CO2, into a sealed container filled with cold, flat beer. More gas than the container can actually hold is pumped in, which creates pressure. Over time, the beer absorbs most of the gas and becomes carbonated. This is why beer and other carbonated beverages continue to remain fizzy even after the initial release of pressure when their containers are opened.
The other method of carbonating beer is natural fermentation. This involves adding a small amount of sugar to the beer before bottling it. In this case, the yeast that remains suspended in the liquid consumes the sugar, fermenting it into alcohol and CO2. The amount of alcohol produced during this secondary fermentation is negligible, while the CO2 produced is just enough to carbonate the beer.
Similar to the forced carbonation method, the CO2 produced through natural fermentation exceeds the capacity of the container (in this case, the bottle), so the beer is forced to absorb it. As the sugar is being fermented, the yeast is also reproducing, and then it either dies or becomes dormant and settles at the bottom of the bottle, creating the whitish layer.
Does the Yeast Affect the Flavor?
In most cases, the dead or dormant yeast cells collected at the bottom of your beer bottle have very little impact on the flavor of the beer. Yeast often makes the beer appear cloudier, especially when poured into a transparent glass, but that is about it. However, in certain styles of wheat beer, the yeast does enhance the flavor, usually making it slightly spicier. This flavor enhancement is more pronounced if the yeast is mixed in with the beer during pouring.