And Slaters Go Plop

q = (b*r)/100

The quality of your brew (out of 100) is equal to the number of batches (to a maximum of 100) you have brewed multiplied by how highly you rate it (out of 100) and divided by 100.

(Or, in plain English: “The beer you make yourself doesn’t taste nearly as good as you think it does, especially when you first start out”)