Boiled water 67.8mg/l (as CaCO3)

[DrewBrews]

My normal water treatment has been to boil for half an hour with a teaspoon of gypsum and add campden tablet.

I've not been very scientific about it, and after a discussion about CRS at the Cambridge home brewers meeting I decided to think about it a bit more carefully.

I got myself a Salifert KH/Alk test kit and tested water straight out of the tap. I then boiled some water for about half an hour (no gypsum) and tested again.

Results:
Unboiled 267.7 mg/l (CaCO3)
Boiled 67.8 mg /l (CaCO3)

I've got three questions:
1)Does the boiled value look reasonable? (I hoping it might be a bit lower)
2)How would my normal gypsum addition affect this result?
3)Would this level of residual carbonate hardness be acceptable when brewing pale beers?

[I have also read G.W's suggestion that small suspended particles of precipitated CaCO3 might affect the reading so I ran the boiled water through a coffee filter and tested again (the result was unchanged)]

[Graham]

I think your water will be fine at 68.

Your true alkalinity is probably lower. The test kits tend to overestimate at low alkalinity levels, because the pH that the indicator changes colour is pH4.5, but at low levels it should be closer to pH5. It's close enough though.

Adding calcium to the boil (at the beginning), will (should) reduce the amount of carbonate by 15-20ppm, perhaps much more, depending upon your water chemistry.

Suspended particles are a potential problem only at low levels because the chalk crystals do not grow large enough to fall out of suspension, or at least fall out of suspension within a reasonable amount of time.

Additional calcium will compensate for higher carbonate. If your mash pH is too high, add a bit more gypsum next time.

Remember that boiling reduces the calcium too, so you will need to put some back with gypsum or calcium chloride

[DrewBrews]

I think your water will be fine at 68.

Your true alkalinity is probably lower. The test kits tend to overestimate at low alkalinity levels, because the pH that the indicator changes colour is pH4.5, but at low levels it should be closer to pH5. It's close enough though.

Adding calcium to the boil (at the beginning), will (should) reduce the amount of carbonate by 15-20ppm, perhaps much more, depending upon your water chemistry.

Suspended particles are a potential problem only at low levels because the chalk crystals do not grow large enough to fall out of suspension, or at least fall out of suspension within a reasonable amount of time.

Additional calcium will compensate for higher carbonate. If your mash pH is too high, add a bit more gypsum next time.

Remember that boiling reduces the calcium too, so you will need to put some back with gypsum or calcium chloride

Thanks for the advice Graham.
I'll add some more gypsum after the initial boil next time I brew. I do sometimes end up with a mash pH of around 5.6 which could probably be a little lower.

Do the sulphate ions from the gypsum contribute alkalinity? ie would replacing some of the residual carbonate with sulphate mean that the result of the salifert test would be the same (but the liquor improved)? Or would I be able to measure a change with the kit?

I may be misunderstanding you but I think from what you said about gypsum lowering the pH that sulphate ions don't contribute as much alkalinity as the carbonate ions.

I'll try another test boil with some gypsum when I get a chance.

[jubby]

I did exactly what you have done Drew and Graham gave me the same advice. My alkalinity pre-boil is 234mg/l CaCo3. Post boil 50, but i added the calcium to the treatment boil which lowers the alkalinity a little more. The mash ph is always spot-on for me using this method. My water has a higher sulphate to chloride ratio, yours may be similar. So i have found that using a little calcium chloride as well as gypsum helps pale ales & bitters. it gives a fuller malty profile, especially in weaker beers. Gypsum on it's own, I have found is good for high ABV beers. The White Shield you tasted has 1/3 calcium chloride, 2/3 gypsum (of the added calcium) to give you some idea.

[Graham]

Do the sulphate ions from the gypsum contribute alkalinity? ie would replacing some of the residual carbonate with sulphate mean that the result of the salifert test would be the same (but the liquor improved)? Or would I be able to measure a change with the kit?

No, sulphate does not contribute to alkalinity. The added calcium, as part of the gypsum, should cause more chalk to precipitate, and you should be able to measure this with the kit as a reduced alkalinity. It is a chemical equilibrium thing. You should find more information by searching for something like "solubility product of ions" or "common ion effect".

There is separate possible issue whereby some waters may not have enough calcium in solution to bind with all the carbonate in solution, thereby it can't form chalk and precipitate. Adding calcium will help here. However, I don't think this is probable with modern municipal waters; i've only seen it in old-time London well water and the water of some German brewing centres; always those areas that traditionally specialised in dark beers, and they specialised in dark beers because even boiling would not get their carbonate low enough, and robs them of calcium anyway.

I may be misunderstanding you but I think from what you said about gypsum lowering the pH that sulphate ions don't contribute as much alkalinity as the carbonate ions.

Gypsum does not in itself lower the pH of the water. The effect on water is due to the common ion effect mentioned above and only reduces alkalinity by a few ppm, only when boiling, and will effect pH of the water even less.

The effect of the calcium part of gypsum is on the mash whereby it reacts with stuff in the malt and reduces the pH of the mash - not the water used for the mash.

Sulphate has no effect on the water or the mash. You can use calcium chloride to lower the pH of the mash the same way. The reason that we use calcium sulphate or calcium chloride is that calcium has to be bound to something; it does not exist on its own. You cannot go into a chemist and buy a bottle of calcium.

[DrewBrews]

Thank's for the advice Graham, it will allow me to me at least a little scientific about my water treatment from now on.

Jubby, How did you find out the sulphate/chloride ratio of your water?

[jubby]

Jubby, How did you find out the sulphate/chloride ratio of your water?

You need to contact Cambridge Water here: http://www.cambridge-water.co.uk/home/contact-us

Ask them for all the parameters required by Grahams water calculator ( Sodium, Chloride, Sulphate, Calcium, Magnesium and Alkalinity)

They are very helpful. I ask for these once a year and they always reply fairly quickly.