According to German beer expert Professor Back, this paper divides beer harmful bacteria into five levels, namely: obligate beer harmful bacteria, latent beer harmful bacteria, indirect beer harmful bacteria, indicative microorganisms and latent microorganisms, which affect the taste of beer.

When the wort is boiled to the second half or before the end, use a clean conical flask to sample 250-300ml, put it at room temperature in the saccharification room, and let it cool down to room temperature. Observe the wort in the conical flask. Or muddy precipitation, the wort in the bottle is evenly distributed with a large number of aggregates, which can be flake, flocculent, etc.