I’ve just started brewing extract kits again, after about 2 years, and noticed something that I didn’t pay attention to before.
First brewed a Cream Ale, but forgot to measure OG when transferring to fermentation. Therefore at the end of fermentation I just used the OG on the box (1.048) and the FG I measured (1.01) and got ~5% ABV.
Second brew was an Amber Ale, this time I did measure OG when transferring to fermentation and noticed OG was 1.036 (instead of 1.047 on box). FG was measured at 1.01, giving me only ~3.4% ABV. However if I use the box OG, it calculates to ~4.9% ABV.
My question is, what can be causing the discepancy between the measured OG and the stated (box) OG?