Brupaks DWB water treatment powder (previously known as DLS) is a carefully controlled blend of inorganic salts to increase the calcium and sulphate content of brewing liquor. A full description of the major constituents in brewing water and their importance to the brewing process is available on the website of "Murphy and Son", the manufacturers of AMS, DWB and many other chemicals and additives used by the brewing industry, and can also be downloaded HERE.
It is usually added in two stages, the first addition being into the dry grist prior to mixing into the Mash and then the remainder to the wort at the start of the boil period (This is Brupak's advice, which is slightly different from that provided by Murphys, the product manufacturer). The amount to be used will vary depending upon the nature of the initial brewing liquor and the style of beer being brewed.
A typical Bitter requires a calcium content of 180-220 p.p.m. Once you have checked and adjusted your brewing liquor with AMS to reduce the carbonate levels, if required, you may need to adjust the Calcium levels in the water.
The Brupaks website provides the following guidance:
The quantity of DLS required can be ascertained from the table below.
DLS in grams per litre
The table shows that in order to increase the calcium content by 125 p.p.m you will need to add 0.7 grams of DLS per litre.
When making a full mash brew, DLS should be added in two stages:
Stage 1. Weigh sufficient DLS to treat your mashing liquor (e.g. 10 litres x 0.7 = 7 grams). Mix DLS into the dry grains. This is most important as adding it to raw liquor will not affect the mash pH.
Stage 2. Weigh sufficient DLS to treat the balance of the total brewing liquor (e.g. 20 litres x 0.7 = 14 grams). Add to the wort at the commencement of the boil.
Extract brewers should add the total amount of DLS to the wort at the commencement of the boil.
From the above information you should be able to treat almost any water to brew first class Bitters and Pale Ales. Other styles of beer, however, require different levels of carbonate and calcium. These are the recommended alkalinity and calcium levels for the most common beer styles.
Bitter and Pale Ale. Alkalinity as CaC03 - up to 50 p.p.m. Calcium - 180 to 220 p.p.m. Mild Ale. Alkalinity as CaC03 - 100 to 150 p.p.m. Calcium - 90 to 110 p.p.m. Porter and Stout. Alkalinity as CaC03 - 100 to 150 p.p.m. Calcium - 100 to 120 p.p.m. Pale Lager. Alkalinity as CaC03 - up to 30 p.p.m. Calcium - 100 to 120 p.p.m.
Your local water board will be able to provide you with a full water analysis to enable you to decide whether on not you need to perform water treatment.
The example provided above was taken from Brupak's website. Murphy and Son, the manufacturer of DWB has slightly different usage instructions if you are adding more than 0.75g/l and suggest that 2/3rds of the overall DMS should be added to the Grist, with the remaining 1/3rd added to the sparge liquor. A full description of DWB and its usage can be found in Murphy's Technical Information Sheet available HERE.
Murphy's information also states that DWB adds 15.4 ppm (actually stated as mg/l) of Chloride and 32.5 ppm of Sulphate when added at the rate of 0.1g/l, so in the above example approx 125 ppm of Chloride and 235 ppm of Sulphate will be added when using 0.7g/l to increase the Calcium content by 125 ppm. They also state that an "average bitter" would normally have up to 400ppm of Sulphate and that best results will be obtained if you have around twice as much Sulphate as Chloride.
Having said this, John Palmer's "How to Brew" book states that the famous "Burton Water" can contain upto 800+ ppm of Sulphate and as little as 16ppm of Chloride, so if the addition of DWB would tend to take your Sulphate levels above the 400 ppm "typical" target when you take your exisiting Sulphate levels into account, you can usually just accept this and not worry too much.