So many little things to learn and explore so little time to invest. Recently I mentioned to John that Campden tablets were a mystery to me. So a little research later and now we are discussing the differences between chloramine reduction and microbial shelf stability.
Campden tablets are metabisulfite pressed into a useful tablet format. Premeasured for convenience. I suppose that using the term Campden tablet is a little less intimidating to chemistry-phobes than potassium metabisulfite. Metabisulfite comes in two forms normally; as sodium or potassium salts. Most of the time we default to potassium versions because the addition of more sodium to our beer (and maybe our diets) is less desirable.
Metabisulfite can act as a reducing agent in water. When it reacts with chloramine the sulfite portion will displace the positively charged amine portion of the chloramine molecule. That leaves the chlorine anion to combine with hydrogens in the water. Free chlorine can then be left to dissipate when you leave a brew kettle full of water to sit overnight. Or you can boil it. But that costs fuel and energy and time to chill again prior to mashing. WOW, that was a lot of chemistry.
Metabisulfites are also useful for microbial stability. In short, sulfites serve to disrupt the metabolic processes that allows most yeasts and fungi to proliferate. However, they do not necessarily kill intruding microbes. When the metabolic rate begins to fail microbes will go dormant I order to prevent themselves from dying. Due to that fact sulfites are normally considered microbial static. Their success as a stabilizer depends on the initial microbial count (microbial load) in beer to must to be low. Low of course is a relative term and hard to define. Generally, you can add sulfite to a must to retard the proliferation of wild microbes and provided you pitch a substantially high enough amount of cultured yeast you’ll still get fermentation. Campden tablets can also be added to a finish wine after flocculation to stabilize it prior to back sweetening.
This works especially well when done in combination with sorbets. Another preserving agent added to musts and wines… But that’s a topic for a different video.