Brewers obtaining their water from municipal systems of moderate size and up are likely to find that the supplier has used chloramine as part of its disinfection process. Chloramine is not as good a disinfectant as plain chlorine but it is more stable which means that it persists in water longer than chlorine does so that no matter where you are on the distribution system there will still be a good chloramine residual in your water when it arrives at your house and it will be safe to drink. This same stability which is beneficial from the safe water point of view presents a problem for brewers: chloramine is harder to remove from water than chlorine is by the conventional means of allowing the water to stand or by heating/boiling it. Both those methods do work but they take longer. Standing can, depending on the level of chloramine, take days and boiling hours.
Choramine is simply ammonia (NH3) in which one or more of the hydrogen atoms has been replaced by chlorine thus NH2Cl is monochloramine which is much more common than dichloramine or nitrogen trichloride, the other two members of the family. It is typically introduced into drinking water by injecting ammonia gas into water which has previously been chlorinated.
The first thing a brewer wants to know is if chloramine is a problem for him and, of course, the second is what he should do about it if it is. It is quite simple to test for chloramine. Simply draw a tumblerful of the water in question and let it stand over night. That is long enough for any free chlorine to leave the water meaning that any detectable chlorine smell the following day is from chloramine. If, the next morning, no chlorine smell is noted confirm this by pouring the water back and forth into another glass which sniffing in the vicinity. Failure to detect chlorine odor while doing this verifies that chloramine is not present at significant levels. If chlorine is smelled then chloramine is indeed present. Brewers can also buy inexpensive test kits but need to be sure that any kit tests for both total and free (with the difference being chloramine) chlorine.
Chloramine can be removed from drinking water by filtration through active carbon filters but the contact time required is long so that unless the filter has very large contact area the flow rate will have to be small. RO systems contain activated carbon filters to protect the membranes from chlorine/chloramine so brewers using those will not have to worry further about chloramine other than being sure they are replacing the filter frequently enough.
The simplest way to surely remove chloramine is through the use of sodium or potassium metabisulfite often sold in the convenient form of 'Campden Tablets' by brewing and wine making suppliers. To use Campden tablets put one in a glass and crush it with a spoon. Add some warm water and stir. It will be hard to get it all to dissolve but it doesn't have to. Put the water to be treated in a pot, kettle or what have you. Add bits of the liquid from the glass a little at a time and stir. Then agitate the treated water and sniff. If you still smell chlorine add a bit more of the liquid. Keep doing that until you don't smell chlorine any more. The reaction is instantaneous. If you smell a bit of sulfur dioxide, that's fine and confirms you have gotten rid of all the chlorine - chloramine and any free chlorine as well. If you conclude that you smell sulfur dioxide be sure it is coming from the water - not your hands or the glass with the Campden tablet in it. The latter will smell strongly of sulfur dioxide (metabite is often referred to as 'solid sulfur dioxide'). You should need half or less of a Campden tablet to treat 10 gallons of water. If you find you are needing more you are probably doing something wrong as 1 typical tablet will treat 20 gal of water chloraminated (no free chlorine - this is the worst case) to 3 mg/L free chlorine equivalent. This depends somewhat on the weight of the metabite in the Campden tablet and whether the salt is potassium or sodium metabisulfite. If Campden tablets are not available from your LHBS or by mail order you can use potassium (or sodium) metabisulfite available from wine making hobby suppliers. Doses are given in the table below.
Brewers are often concerned about the consequences of adding metabite to their water. They are not significant. When chloramine is reduced by metabite the reaction products are ammonium ion, chloride ion, sulfate ion, hydrogen ion and potassium or sodium ion depending on whether potassium or sodium metabisulfite was used. For each mg/L of chloramine destroyed 0.51 mg/L ammonium ion is released. This is a beneficial yeast nutrient. Also 2.70 mg/L sulfate and 1 mg/L chloride ion and enough hydrogen ion to neutralize 1.43 mg/L as calcium carbonate alkalinity are released into the water as are either 1.1 mg of potassium or 0.65 mg of sodium. As chloramine levels rarely exceed 3 mg/L the recommendation of 1 Campden Tablet per 20 gallons of water treated covers the vast majority of cases. The method of gradual addition given above insures that the minimum amounts of these ions are introduced but one can always choose to be on the safe side and use the whole tablet for 20 gallons. Unreacted metabolite becomes sulfur dioxide in solution which either is driven off when the water is heated or reduces something in the mash and this is a good thing.
The table below shows how much of what is needed to remove each mg/L chlorine and chloramine and how much of what byproducts are produced. Details of the calculations can be found at http://wetnewf.org/pdfs/Brewing_arti...T_Chlorine.pdf
As there have been several questions recently (1/13) about the use of ascorbic acid to reduce chloramines I'm adding the following remarks:
Ascorbic acid is effective at reducing chloramine. The required dose is 4.97 mg/L of water treated per mg/L equivalent free chlorine (if the water report lists chloramine at 2 mg/L then the equivalent free chlorine is 2 mg/L). This is equivalent to 1.13 grams for the 20 gal at 3 mg/L that is treatable with 1 Campden tablet. My concerns with ascorbic acid are 3:
1. It has a finite shelf life
2. While ascorbic acid does not behave as an acid in the chloramine reaction any excess does. If, for example, you think chloramine is at 2 mg/L and it is actually at 1 you will add an extra 4.97 mg/L. As it's a pretty strong acid that's enough to lower the pH of distilled water to pH 4.29. Water with higher alkalinity will not be so dramatically effected. Water with alkalinity of 10 would go to pH 6.22. While this isn't probably terribly significant in a mash that has typical buffering capacity (much greater than that of the water) you should, if using ascorbic acid, use the incremental addition process and stop as soon as the chlorine smell is gone.
3. The products of the reaction are, as with metabite, ammonium ion and chloride ion but rather than sufate ion we get oxidized ascorbic acid (dehydroascorbic acid) which is pretty chemically active. For example, it degrades valine to isobutyraldehyde and, in the presence of certain metal ions, can act as an oxidizer. That is why, when it is added to beer to keep beer in a reduced state (stabilize it) it is always accompanied by metabite.
Given these concerns I recommend the use of metabite rather than ascorbic acid.