A question about water chemistry

Brewer-#383037

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?
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 some say 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.
I know some of this is a matter of taste. Just want to avoid ruining a batch.

BarbarianBrewer

Welcome to the Brewer's Friend Forum!
The dark malts in a stout will not only help drop your pH, they will also hide flavors contributed by the small amount* of lactic acid or saurmaltz you may need.  I only use phosphoric when I am brewing something lite and will therefore need more for mash pH adjustment.

Mark-Farrall

Are you using the BF water calculator that is linked in the recipe? That would be my suggestion to determine what salts need to be added. As @BarbarianBrewer stated, the dark malts will drop your ph. In all my stouts and porters I’ve never had to add acid. However, I do use a little baking soda to raise the ph. The 5.5-5.6 range is good for me. Also, I gave up using a ph meter some time ago as I found it to be a very “needy” tool in terms of calibration and storage. I use the BF water calculator to determine what adjustments need to be made to ph and haven’t had any issues.

Donoroto

pH constantly changes throughout the brewing process, including the mash. Even with water that's relatively free of buffering compounds the grains add enough to slowly drop the pH throughout the length of the mash.
With roasted grains you're far less likely to need acid to drop the pH. For my basically neutral starting water and a dark grain bill I'll be looking at a pH of 5.3 or lower. With more roast grains I might actually need something alkaline to raise the pH.
I'm also not sure how the lower starting pH from the roasted grains will change the slow decrease of pH. The times I've heard it discussed it's been for non-roasted grain bills. It may actually slowly raise during the mash if it starts fairly low.

The-Brew-Mentor

The pH of the starting water is not very important. The grains will overwhelm whatever is in the water regardless.
A second vote for the water calculator. It is a separate calculator that can be called up from the recipe editor. Pick a water profile (e.g., 'London, Porter') and play with the salts to get close to what it says. You should assume 100% RO water unless you know your tap water's profile. Then export the recommendations back into the recipe.
Let us know if you have questions

Nosybear

Also, I think you'll be better served with a gram scale than a teaspoon.

Yooper

Just make your beer and read John Palmer's "How to Brew" to learn why you're putting stuff in your water. My guess is that you read all this stuff on a homebrew forum somewhere and got the idea you had to do all of it. If you had to cut your water 90 percent with RO, chances are it was good for a stout to begin with. Simplify!

BarbarianBrewer

Not to toot my own horn, but I suggest reading this three part series:  https://www.brewersfriend.com/2017/11/19/brewing-water-basics-part-1/
It's sort of the most basic explanation of brewing water ingredients, and what they are and what they do.  Just like with cooking, without tasting you don't add salt and pepper to your dish.   While you can't taste your beer before you make it, you'll want to know why and if you should add those "seasonings" (gypsum and calcium chloride are salts).   if you don't know why you're adding something, then don't add anything at all.  
What's your beginning water?  If it's RO or distilled, skip the sauermalz!