To determine the ABV contribution of individual grains, you first need to calculate the beer's total ABV. Then, for each grain, multiply its weight by its PPG or potential yield value. By adding up the total points value of all grains in the grain bill, you can find the percent contribution of each grain. Applying these percentages to the beer's total ABV will give you the ABV contribution for each grain. However, it's essential to note that there's no official formula for this, and the results should be taken with caution.