Dear Mr. Wizard,
I recently moved to a city that uses chloramine in the water supply. Looking for suggestions in removing these chloramines from my brewing water, I posted a question to an online brewing board. It was suggested that adding sodium metabisulfite to the water would clear the beer of this compound. Is this true? How does it work and what would be an approximate amount to add per gallon?
Mr. Wizard replies:
This is an interesting question and I did some digging to come up with a good answer for you. Dechlorination is important to brewers for flavor reasons. Compounds called chlorophenols are formed when beer interacts with chlorine and these compounds have a fairy unpleasant aroma. Dechlori-nation is also important to municipal water authorities in the event that chlorinated water needs to be discharged into the environment.
Although many reducing agents can be used to dechlorinate water, the ones that are most accessible to homebrewers are sodium metabisulfite or its cousin, potassium metabisulfite (commonly found in the Campden tablets used by winemakers). These compounds will remove chlorine from both sodium hypochlorite (bleach) and chloramine treated waters. The reaction converts chlorine into chloride and the sulfite is converted to sulfate. Chloride has no affect on aroma, is found in most water and is added by many brewers in the form of calcium chloride. Likewise, sulfate is a normal constituent of water and is added in the form of calcium sulfate by brewers. When this reaction occurs with chloramines, there are also ammonium ions released into the water. Again, this is no big deal because ammonium ions are found in a brewers mash and come from the malt. Keep in mind, we are talking about very low concentrations of all of these reaction products due to the low concentrations of chlorine and metabisulfite involved in the reaction.
Although chlorinated water has a strong and easily identifiable aroma, the concentration of free chlorine is usually less than two parts per million. The dechlorination reaction requires 1.47 mg of sodium metabisulfite to reduce 1 mg of free chlorine. In practice, this ratio is increased two–three fold. In easy to use terms, a 1/2-ounce Campden tablet can be used to dechlorinate 20 gallons of water. This reaction occurs very rapidly and all you really need to do is dissolve the metabisulfite in your water, let it sit for a minute or two and you are finished with the dechlorination process.
Many brewers boil water prior to use to drive chlorine out of the water. The boiling method works very well with water chlorinated with hypochlorite, but is less effective at removing chloramine. The metabisulfite method is fast acting, easy to perform and very effective.
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