Metabisulfite as Dechlorinator

Chlorine is the enemy of good beer made with tap water.  Chlorine reacts with phenols to form chlorophenols, chemical flavors reminiscent of a band-aid, harsh and very detrimental to beer’s flavor.  I don’t react well to harsh flavors so for years I’ve tried to drive them out.  The final frontier was the chlorine in tap water.

Our tap water here in Aurora is good for brewing and very low in disinfectant – the role chlorine plays.  The city uses both chlorine and chloramine, a more complex, more stable chlorine disinfectant and one much harder to get rid of.  Boiling or simply letting water stand will get rid of chlorine or chlorine dioxide, another gaseous disinfectant sometimes added to tap water.  But chloramine is persistent and reacts to form chlorophenols.  And it is much harder to get rid of.

Three primary ways are available to homebrewers to get rid of chlorine in tap water.  Reverse osmosis (RO) filters for home use are available and they get rid of everything.  The water comes out close to pure, so close you can treat all the ion concentrations as zero, chlorine included.  At some point, I’ll likely consider getting an RO filtration system and building my brewing water for each style but for now, I have other things to invest in.

Larger breweries use activated charcoal filtration.  Activated charcoal filters are available for home or RV use and I used one for years before learning that the water has to be in contact with the filters for a significant amount of time to remove chlorine and chloramines.  Long story short, these filters alone are not likely to remove all the chlorine in your water unless as a stage in a RO filter.

The easiest and cheapest way I’ve found to dechlorinate is using metabisulfite, either potassium metabisulfite or sodium metabisulfite, commonly known as Campden tablets.  Ground and added to tap water, a single Campden tablet is sufficient to dechlorinate 20 gallons of water and at that concentration, has no ill effects on yeast.  I generally use 10 gallons of water for a typical brew so I just grind up the tab and add it with my brewing salts.  The net result is the chlorine and chloramine is reduced to near zero and the reaction forms a negligible amount of chloride and sulfate, with some sulfite formed that will boil off.

When I started using this procedure, I noticed quickly that I could smell the chlorine before adding the metabisulfite but not afterward.  This was not enough.  So I got some chlorine test strips and ran the test.  I checked my water before adding the metabisulfite.  The concentration of total chlorine was about 5 ppm.  After adding the metabisulfite, the concentration was close enough to zero that the strips could not detect chlorine.  That’s good enough for me.

I still detect a lot of chlorine at Homebrewer’s Night, when I sample beers from several homebrewers at our local homebrew shop.  It’s so quick and easy to remove chlorine, it should be one of the steps in every brewer’s brew day, at least those of us using municipal tap water disinfected with chlorine.  A ground-up Campden tablet is our key to smoother beer with no chemical flavors.