The processing also dissipates some of the honey's aroma. Crystallized honey is normally acceptable for mead. First, it generally indicates less processing, since one of the reasons for processing honey is to keep it from crystallizing. Second, it may be cheaper because it's less appealing to the average consumer. To re-liquefy crystallized honey so you can pour it, just heat it gently.
Yeast prefer an acidic environment.
Many other micro-organisms don't. The acid you add protects the must until the alcohol level creates a hostile environment for the competition. Acid can be added in many forms. Winemaking suppliers sell acid blends, powder or liquid. For example, if the must is 0.5 percent acid as tartaric, it is as acidic as if 0.5 percent of the must were pure tartaric acid.