Apparent attenuation is the measurement of the percentage of sugars that have been converted to alcohol by the yeast in a beer. Apparent attenuation is equal to the original gravity minus the final gravity divided by the original gravity, showing the percentage of conversion. A typical apparent attenuation range is between 65 and 80%.
Apparent attenuation calculation example:
Original Gravity of sample beer = 1.06
Final Gravity of sample beer = 1.012
Calculation: 1.06 – 1.012 = .048
.048 / .06 = 80% Apparent Attenuation
There are a variety of ways to impact your apparent attenuation. Some of these include the type of yeast you use, the amount of yeast you pitch, your mash temperature(s), your grain bill composition, and your mash PH. If you are doing extract brewing, then the primary impacts will come from your yeast and any unfermentable sugars that you may add, such as maltodextrin.