Carbonate reduction may be performed in a couple of ways. Carbonate levels can be lowered to the 50-150 ppm range by two methods, boiling or dilution. The problem with boiling is that it can only remove the temporary hardness (which is the lesser of the total alkalinity and CaCO3 or the total hardness as CaCO3).
(In chemistry, Carbonate Formula: a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, CO3-2 but may also mean an ester of carbonic acid, an organic compound containing the carbonate group C(=O)(O–)2. Bicarbonate formula: Bicarbonate is a polyatomic anion with the chemical formula HCO−3. Bicarbonate serves a crucial biochemical role in the physiological pH buffering system). Source: Wikipedia
Using Slaked Lime for Carbonate Reduction
Another way of performing carbonate reduction involves adding slaked lime or “pickling lime” to the water. The problem with this method is that you must calculate the amount of lime to add carefully, and it must be added gradually while monitoring the pH carefully to avoid creating very alkaline water from excess hydroxide. For those wanting to try this method of carbonate reduction, here is how John Palmer suggests doing it in his book, How To Brew. I’ll calculate using my water profile and 10 gallons of water.
- Add 1 teaspoon of chalk (calcium carbonate) for each 5 gallons of brewing water to be treated.
- Multiply the temporary hardness by 0.74 for a rough idea of the milligrams of lime needed to treat 1 liter of water. In my case the temporary hardness is 80 ppm, so 80×0.74=59.2 Then multiply this number by the number of liters of brewing water to be treated, and divide by 1000 to get the number of grams to treat the entire 10 gallons of water. To get everything in the correct units, 10 gallons of water equals just under 38 liters. So, 59.2 milligrams x 38 liters of water / 1000 grams per milligram = 2.25 grams slaked lime.
- Increase the 2.25 grams by 20-30% (I’ll use 25%) 2.25 x 1.25=2.8 grams, put this in a beaker or flask with enough water to get the lime in suspension.
- Here’s the hard part: add the slurry above to the water in an initially large and then smaller increments, stirring thoroughly and checking the pH after each addition
- Keep adding the slurry of lime and water fairly quickly until the pH reads between 9.5 and 10.
- Now, monitor the pH for a while. As the carbonates precipitate, the pH will fall.
- Keep adding small amounts of slurry to maintain the pH in the 9.5-10 range.
- The pH will continue falling as the water incorporates CO2 from the air, but the rate of drop will begin to slow down. When it does begin to slow down, stop adding the lime and let the water sit to allow the precipitate to settle to the bottom.
- After the precipitate has settled to the bottom, siphon the water off the sediment. Measure the hardness and total alkalinity. This may be beyond the abilities of your lab, but you can take a sample into a pool supply store and tell them that it is the water you want to use to fill your spa with. They will measure the properties and give you a report back with recommendations on how to treat it. You may get
a hard sell for pool/spa chemicals.
Dilution – The Easy Way to Reduce Carbonates
Probably the easiest way (after reading the above procedure you can see why) to accomplish carbonate reduction in your brewing water is by dilution with distilled water in a 1:1 ratio. Doing this will effectively cut your carbonate levels in half. Adjust the ratio accordingly. So, if you want to brew a pilsener with hard water, dilution of your hard water with distilled water is the easiest way. For example, if my total hardness as CaCO3 was 80 ppm, and I wanted to lower my carbonate levels to below 50 ppm in 10 gallons of brewing water, I’d have to dilute with 83.33% distilled water. If I try to boil my 10 gallons of brewing water to remove some of the carbonates, I’d only be able to remove approximately 30 ppm, which would get me down to the 50 ppm solubility constant of calcium. That’s not much of a reduction for so much work and propane. Dilution is obviously the best way to go in this example.
Reference: Information for this article was taken from John Palmer’s book How To Brew.