pH of both the mash and the sparge are very important. With water as salt ladened as Adelaide's you can adjust the sparge with phosphoric or lactic acid to lower it to about 5.7 at "room temp" which will fall due to dissociation of the hydrogen ions as the temp rises.
At the end of the sparge the pH should still be below 6. This is not as important for batch sparging as for continuous sparging.
With a light coloured beer sparge pH should be kept below pH of 6. A lighter coloured beer with darker roasted grains should maintain the sparge pH within the above range. However if the pH of your town water is high these slightly acid grain may not keep the grain bed ph in the range you want and it is times such as these that acidifying the sparge is called for.
There is howver little point worrying about pH of the mash or the sparge without a means of accurately measuring it.
Don't just assume -- measure.
I routinely adjust my mash and sparge but I do it with a meter.
Now -- gypsum.
This is calcium sulphate and the calcium component is very important to assist the enzymes in the malt to reach the correct pH [See the recent very good explanation on correct mash pH on craft brewers by David Lamotte]
Acidification of the mash is primarily done by the enzyme phytase, which is active at 30 to 53C and breaks down insoluble phytin, a complex organic phosphate containing both calcium and magnesium, to phytic acid. Phytic acid has a strong affinity for calcium ions, and it forms calcium phosphate and releases hydrogen ions in the process. Inorganic malt phosphates also react with calcium to release hydrogen ions, but the phytic acid reaction is more efficient. When mashing, phytase activity is greater with under-modified malt than with highly modified malt. Highly modified malts have very little phytase because of the high kilning temperatures.
The nature of the mashing water has an important influence on mash reactions. The ions of major importance at mashing are those of calcium and carbonate, with magnesium and sodium ions playing lesser roles. Calcium lowers the pH of the mash mainly by its interaction with phosphates and to a lesser degree with protein from the malt. Carbonate ions operate in the reverse direction.
If the water of the mash has insufficient calcium it will not reach correct pH. If this occurs and it often does mash efficiency levels can suffer.
A beer with a high proportion of dark malts can become too acid [pH level too low] and this can be a rare time to add Calcium Carbonate to the mash. Calcium Carbonate is normally an insuluable salt in water but because of mash acidity a reaction takes place and the ph of the mash can be held in the correct range.
Due to the strange composition of Adelaide water gypsum is a good water salt to add and if you do, keep the ratio of Sulpates to Chlorides at [as close as you can] 2:1
eg ... 100/50 or 300/150
Refer to the Murhy's site for information on this ratio.
http://www.murphyandson.co.uk/brewing_articles.htm
Depending on the water I'm brewing with I use gypsum [Calcium Sulphate] and/or Calcium Chloride.
Calcium Chlorideis not advisable to add to Adelaide water because of the rather high existing Chloride levels.
If you wish to structure a particular water profile you can guesstimate rain water as "reasonable" salt free [it isn't really] and adjust using a good set of scales and the following
Epson Salts -- Magnesium Sulphate [chemist]
Gypsum -- Calcium Sulphate
-- Calcium Chloride [Sometimes hard to find]
Chalk -- Calcium Carbonate
Table Salt -- Sodium Chloride [Must not be iodised -- harmful to yeast]
-- Sodium Bicarbonate [Strongly alkali]
These salts are all you need to achieve a good facsimile of any brewing water.
The "Calcium" rule for good mash efficiency is a minimum of 50ppm.
Don't attempt to gues salt weights. Weigh them and use BeerSmith or equivelant to help determine the salts to add. Doc mentioned a downloadable utility program for water chemistry that is very handy.
You cannot accurately dump acid into the water you have and hope. A pH meter is not that costly. Then when you have one you can acid wash yeast as well.
The above applies to mash brewing because you have the ability to control your processes.
Steve
