Delayed CaCO3 with roasted grain addition?

I am brewing a double oatmeal stout in a few days, and plan to add the roasted barley and chocolate malt at about 5 - 10 minutes before sparging. I have very soft water (HCO3 23ppm, every other ion under 6 ppm), and plan to add chalk to increase alkalinity. I feel like if I add the chalk long before the roasted grains, the pH will be driven too high for most of the mash. It seems like the answer should be obvious, but should I add my other mineral additions (gypsum, NaCl, and CaCl) to the strike water but hold off on the chalk until I add the roasted grains? On the other hand, this might overshoot my calcium levels, so would baking soda be a better choice?

2nd question: I was going to shoot for a London water profile, but the chloride seems low at 20 - 40ppm depending on the source. Should I bump it up?

I'm using the promash water profile calculator (very helpful), and I won't have a pH meter until Christmas.

Thanks for your input.

You should wait until after the Holidays to report back to us what the mash pH was with the chalk. The evidence I've seen shows that chalk does not work AT ALL in the mash and has no effect on mash pH. You should have a nice low pH with that low alkalinity water. If you are concerned about mash pH dropping due to the roast malts, you need to pick up some lime. It actually works, unlike chalk.

Thank you for the info.

]I've never heard that calcium carbonate is not effective. I don't know of any guidelines for using lime or how it would affect hardness, can you make a suggestion based on an anticipated London water profile? And should I add it with the roasted malts, or at the beginning of the mash?

7ways said:

I've never heard that calcium carbonate is not effective.

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I have come across this detail a while back when I found that John Palmer's water spreadsheet didn't get the correct alkalinity from chalk yet the residual alkalinity was still correct.

Here are a few blog posts that shed more light on chalk and its affect on pH in brewing:

http://braukaiser.com/blog/?s=chalk

I don't know of any guidelines for using lime or how it would affect hardness, can you make a suggestion based on an anticipated London water profile? And should I add it with the roasted malts, or at the beginning of the mash?

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despite its shortcomings with regard to solubility I still think chalk is useful for raising alkalinity in brewing. While I, and others, also have evidence that chalk can raise pH only by 0.2 pH points it is also true that a very high residual alkalinity, for which you wold need lots of chalk, is rarely needed.

Depending on the coarsness of your grist, adding roasted grains towards the end of the mash may also caused them to release less of their pH lowering acids. This also limits the need for chalk or baking soda.

On problem you have is that w/o adding the roasted grains at the beginning and w/o having negative residual alkalinity in the water your mash pH may actually end up a bit high. Most pale base malts give you a mash pH of 5.7 in distilled water (pretty much what you have). That means you want to at least add some calcium salts (Gypsum and/or Calcium Chloride) in the strike water. Maybe aim for 100 ppm Ca.

pH measurement of the boil pH may show if you need to add some chalk or some other alkalinity boosting salt to bring it to ~5.4 at the beginning of the boil.

Kai

Thanks for the response Kai.
I've been carefully reading through Bru'n Water and the spreadsheets; what a great tool, it's better than promash!

My mineral additions will cause
Ca 56
Mg 8
Na 39
SO4 43
Cl 64
bicarb 123

I'm satisfied with this profile. But the question remains, should I wait to add carbonates until the last 10 minutes of the mash along with the 2 lbs. of dark malts?

7ways said:

I'm satisfied with this profile. But the question remains, should I wait to add carbonates until the last 10 minutes of the mash along with the 2 lbs. of dark malts?

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I'd say yes.