Brewers who use municipal water for their beers know that it is treated with chlorine for disinfection and that residual chlorine may react with phenols in malt to produce chlorophenols, which lend a plasticlike taste to beer at parts-per-billion levels. Most brewers also remember from their days of keeping pet goldfish that allowing water to stand, aerating it, or boiling it will allow chlorine to escape, thus rendering the water fit for Goldy and for brewing.
In recent years, more water authorities have started to treat water with ammonia in addition to chlorine. This treatment results in the formation of chemicals called chloramines, which are similar to chlorine in that they kill bacteria and aquarium fish and ruin beer.
Standing, aeration, and boiling will remove chloramines from water, but not very effectively. Water in my area (Fairfax County, Virginia) contains the equivalent of 3 mg/L of chlorine in chloramines, a fairly high level. Ten gallons of this water allowed to stand in a 25-gallon stock pot required weeks to lose chloramine down to the <0.1 mg/L level. Almost two hours of boiling is required to get the chloramine in Fairfax County water down to the hundredths of milligrams per liter.
This article explains how to measure chlorine and chloramines in your brew water and how to reduce or eliminate these beer-spoiling chemicals if they are causing you problems.
What Are Chloramines?
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