What's the difference between Potassium Metabisulfite and Sodium Metabisulfite in regards to treating mash water and can either be used to generally bring distilled water to decent alkalinity/pH levels? I'm really not interested in becoming a water treatment specialist or getting the water absolutely perfect at this time. I just want it in a reasonable zone. I've used Accumash in the past but I'm looking for something cheaper and more versatile. Thanks.
I'm unaware that either of these chemicals is commonly used to adjust pH. Sodium metabisulfite is often used to remove chlorine (and I think chloramine as well). It is also used by "low dissolved oxygen" or "LODO" brewers as an "oxygen scavenger." The treatise on LODO brewing published by the German Brewing Forum (PDF) states: "We should note, potassium metabisulfite is not recommended, as an excess of 10 ppm potassium can be detrimental to the mash." To support this statement, the treatise cites "L. Narziss. Abriss der Bierbrauerei. Wiley-VCH, 2005." Assuming the Germans are correct, I would go with sodium metabisulfite rather than potassium metabisulfite. But then, if you are looking to adjust pH, I suspect you should focus on calcium chloride and calcium sulfate, which are the more traditional chemicals used to adjust pH. Any of the common spreadsheets (Bru'nWater, Brewcipher, EZWater) will allow you to input your grain bill and the amounts of calcium chloride and/or calcium sulfate that you wish to add, and will provide an estimate of the resulting mash pH. [edited for formatting and clarity]
The common use is to remove chlorine from the water. It really won't do much for pH. The less common use is as an antioxidant, as in the LODO brewing. Much more is used then, so stick to N-meta.
I (infrequently) use potassium metabisulfite to prevent further attenuation in things I want to backsweeten without using lactose, etc...commonly used with wine.
This was all very helpful. Thank you. My local shop now has little cheap packs of water treatment based on the type of beer you're making that are far cheaper than Accumash so I'll give them a try to simplify things. When I get more time I'll try to familiarize myself with Bru'nWater, Brewcipher, and/or EZWater.
