A Question About Water Chemistry

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Gerry D

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Jul 14, 2022
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I am taking my first dive into water chemistry using the brewing water chemistry primer guidelines and I have a few questions. I am making an oatmeal stout with a total 8 gallons of water at 90% RO/10% Filtered Tap Water. I plan to treat all of the water at the outset with 1.6 tsp of calcium chloride. Should I add equal parts gypsum as well since there are some quite popular British porters and stouts?

I bought a pH meter and plan to check the pH of the sparge water at room temp and adjust it to 5.5 prior to heating it. For the mash I will not make any adjustments until the pH has stabilized, which should take around 20 to 30 minutes.

Since it is an oatmeal stout I plan to use phosphoric acid if I need to make the sparge water/mash more acidic and slaked lime if I need to make it more alkaline since these seems to be the best ways to make pH adjustments without altering flavor. I will be purchasing them at the LHBS when I pick up my grain so I am open to suggestion.

I am interested in using Sauermalz but the primer says to skip it in a stout. I would not want any sourness from the lactic acid in an oatmeal stout. Other than possbile sourness from the lactic acid, what other flavors does Sauermalz contribute? I was thinking about adding the phosphoric acid to the sparge water if I need to make it more acidic but using the sauermalz to the mash if I need to increase acidity.

This is what I gleaned from the many pages of the brewing water chemistry primer and I know some of this is a matter of taste. Just want to avoid ruining a batch.
Did I post this in the wrong place?

Just want to avoid ruining a batch.
If you use start with 100% RO/distilled water, and follow the specific adjustments in the primer (or "cliff notes" version (link)), you will not ruin the batch due to incorrect water adjustments.
I bought a pH meter and plan to check the pH of the sparge water at room temp and adjust it to 5.5 prior to heating it.

When using RO, pH of the sparge water is nearly irrelevant. So nearly irrelevant you may treat it as such. It's the alkalinity that matters and RO has practically zero.

slaked lime

Baking soda

I am interested in using Sauermalz but the primer says to skip it in a stout.

Because the dark roasted malts bring their own acidity.
My experience agrees with that of Ray Daniels, who in his classic book Designing Great Beers from the 1990s pointed out that the baseline mash pH using RO or distilled water is about 5.8 without adding any salts, and that dark roasted grains and crystal malts will reduce mash pH further from this baseline by about 0.3 (to 5.5) when comprising 10% of the grist, and when increased to 20% then the pH is reduced by 0.5 (to 5.3) from the baseline mash pH. If more alkaline water is used, such as my tap water here, baseline pH might be more like 5.9 to 6.1, rather than 5.8, but the same subtractions of around 0.3-0.5 hold true for common amounts of dark and crystal malts.

So, for example, I find that when brewing a dark beer using 15% dark or crystal malts, I can expect to reduce mash pH by about 0.4 from baseline. If I use tap water, baseline mash pH may go from 5.9 to 5.5. If I want lower mash pH, I can use RO or distilled which takes baseline from 5.8 to 5.4.

Any amount of calcium chloride or gypsum additions might reduce pH further by about 0.1 at most (very small impact). Whereas bicarbonate additions can add 0.1 in tiny amounts, like we're talking 1/4 teaspoon baking soda or lime in 5 gallons (a little goes a long way).

Bottom line: You will likely find that using RO or distilled in a stout will take your mash pH too low. If you use salts plus 20% dark malts, you can sometimes end up with a mash pH of 5.1 to 5.2. This is why for stouts I always use alkaline tap water rather than distilled or RO, for the higher baseline mash pH closer to 5.9, then I usually don't need to make any salt adjustments at all, or it would be optional. Never will you need to add acid to a good stout mash. More often you'll need that baking soda or lime, but not always unless you're starting from RO or distilled. With most tap waters, it's alkaline enough that you can skip worrying about water much at all, in a stout.

Pale beers are on the opposite end. For those I'll often start with RO/distilled, with the low baseline 5.8, and still need to acidify to get down to at least 5.5 or 5.6, with even more acid needed if I want it more snappy down to 5.3. Alkalinity would drive this need even further.

Reddish/copper colored beers can be both more forgiving, and/or more complicated, depending on your goals and water source.

That's all for today, I need to get back to work. Cheers. :)
I too tend to over think things as well! When I first took the dive into brewing water, I read the book Water: A Comprehensive Guide for Brewers. (Water: A Comprehensive Guide for Brewers (Brewing Elements): Palmer, John J., Kaminski, Colin: 9780937381991: Amazon.com: Books) To be honest, as interesting as the book is, it just confused me more. In the end, I sent a water sample of my tap water to Brewer's / Water Test Kit - Ward Laboratories, Inc.. This test, at a minimal cost, told me exactly what my water was made of. Then I entered my water profile in BeerSmith, and I'm able to adjust my tap water using camden tablets brewing salts to create water that is true to whatever style I'm brewing. Because my tap water is agreeable with brewing, I haven't used distilled or R/O water in years, and my results have been great. Hope this helps.
Thanks for all of the replies. I ended up using 90%RO/10% filtered tap water and add the calcium chloride at 1 tsp per 5 gallons of water. We'll see how it goes. The pH of the mash turned out 5.3. I did not make any adjustments. Next time I will use 100% filtered tap water with the calcium chloride to see where that gets me.