How much buffering capacity does the mash have?

[Hermit]

My city water is quite flavorless. That is a good thing. It also has a high pH. Try the 10.8 range. I'm guessing they do this to keep from corroding pipes? The calcium is also on the low side compared to the sulfates and chlorides. That makes it a challenge to drive the calcium levels up. But, that isn't the purpose of this post. I digressed right off the bat.....


I only had 3 gallons of RO water for a brew needing 5 gallons. Water calculators have gotten me right on and far off. An out of town job kept me from brewing for close to a year so I wanted to get something in the fermentor. Orfy's mild recipe is one of my go to brews. I decided to acidify the total volume of water and 'break the buffer' and get the pH below 7 and let the mash do the rest. This recipe has a high volume of c60 and a bit of chocolate thrown in.

I got the water down to 6.7pH. Mash after 10 minutes was 5.3.

The question is, how much could the 6.7pH have varied and still have landed on the 5.3? For those of us that can measure and acidify the water would this lead to a closer approxiation on new brews over the current calculator models?

 

[mchrispen]

So through acidification, you dramatically cut the alkalinity of your water. The 10.8 water pH is very odd, but somewhat irrelevant to your needs. It is simply a function of the acid required to titrate your water to an end point.

It appears that what you did worked well. 5.3 is very acceptable, however many folks may wish to mash a bit higher for a mild, say 5.4-5.5. But that is a matter of personal preference.

As to the question in your post title... the answer is that it varies. Base malts, as the largest component of the grist are buffering against acidity of the water, and the presence of crystal/caramel and roasts in the grist. Without a complete recipe - hard to determine. You mention a "large volume of C60" - which suggests that your mash benefited both from the titration of your strike water AND the acidic contribution of the crystal malt.

Relative to your later questions:

The question is, how much could the 6.7pH have varied and still have landed on the 5.3?

I haven't done the math to determine the water's alkalinity as CaCO3, but would bet that you had reduced your alkalinity below 40 ppm. Additional acid would likely contribute a stronger acidification of the mash, resulting in a lower mash pH - this is assuming that residual acid ions are present when you strike.

For those of us that can measure and acidify the water would this lead to a closer approximation on new brews over the current calculator models?

Direct observation of mash pH behavior for a given recipe is always better information than a mash pH estimate, and great information for the next brew of this recipe. This also assumes that you are exactly repeating the behavior, strike/mash volumes and recipe. For example, if you left out a quarter of the crystal 60, it is likely that your mash pH will be higher than 5.3. In my mind, this doesn't replace the need for a mash pH spreadsheet like Bru'n, especially for the homebrewer that seldom brews the identical recipe over and over (pure speculation!) - and the best scenario is a combination of tested observation and estimation before heading into the brew day.

Now - hopefully I got that right.

 

[ajdelange]

My city water is quite flavorless. That is a good thing. It also has a high pH. Try the 10.8 range. I'm guessing they do this to keep from corroding pipes? The calcium is also on the low side compared to the sulfates and chlorides. That makes it a challenge to drive the calcium levels up. But, that isn't the purpose of this post. I digressed right off the bat.....

Nor is it necessary to drive it up. 31 mg/L is plenty for most applications.

I only had 3 gallons of RO water for a brew needing 5 gallons. Water calculators have gotten me right on and far off.

Even a broken clock is right twice a day.

I decided to acidify the total volume of water and 'break the buffer' and get the pH below 7 and let the mash do the rest.

This is a good approach but you don't have much buffering. The only thing weird about your water is that almost half the alkalinity is hydroxide. You can still knock it (and the remaining carbo alkalinity) out my acidifying the water to mash pH. This removes water from the mash acid balance equation. It's proton deficit is 0. All that remains is to balance the proton deficits/surfeits of the grains with acid or base as is necessary.

This recipe has a high volume of c60 and a bit of chocolate thrown in.

These have proton surfeits (negative deficits) at normal mash pH.

I got the water down to 6.7pH. Mash after 10 minutes was 5.3.

In acidifying to 6.7 you used 63% of the acid you would have used to get to pH 5.3. The total deficit of the base malt and the dark grains was a surfeit of 37% i.e. the dark malts supplied enough acid to lower the base malt from its DI mash pH to 5.3 and the water from 6.7 to 5.3.

The question is, how much could the 6.7 pH have varied and still have landed on the 5.3?

You were lucky. Had you gone all the way to pH 5.3 with the water you would have had a lower mash pH but not by very much as your total buffering (T- alkalinity of 54) just isn't that much.

For those of us that can measure and acidify the water would this lead to a closer approxiation on new brews over the current calculator models?

It isn't hard to come up with a pretty robust model of proton deficit/surfeit and thus get very good mash pH predictions if you have good malt data.
. The problems, in order of increasing magnitude, are that most of the calculators don't use a robust model and good malt data is difficult (lots of lab time) to get. I'm dangling the idea that maltsters are the logical ones to obtain this data and include it in their spec sheets. It can then be inserted into a pretty simple spreadsheet (example at http://wetnewf.org/pdfs/Brewing_articles/MashpH.xlsx) and good predictions obtained. Note that this (prediction) does require use of Excels Solver which, for some reason, terrifies people. Bisection methods can be used if you are one of those. See the slides that accompany the spreadsheet at Wetnewf.

By playing around with the spreadsheet you can figure out how much acid to add to the water (or mash but better to the water) to hit a desired pH without using the solver or bisection techniques.


All this is well and good but no model is or ever will be as good as a measurement. If tight mash pH control is your goal then measurement of small test mashes and the full mash is the way to proceed.

 

[Hermit]

I missed something last night. If I click on the 'more info' in the pre-mash water report it shows pH. I adjusted my acid level to show my measured pH. It showed a predicted mash of 5.26 instead of the measured 5.30.

http://www.brewersfriend.com/mash-chemistry-and-brewing-water-calculator/?id=NK8R6VL

To get it up into the 5.4 range I had to drop the acid addition and add 2 grams of bakind soda. So, I guess that answers my question about buffering capacity as a general rule.

http://www.brewersfriend.com/mash-chemistry-and-brewing-water-calculator/?id=YLHFT7P

Anyhow I guess I can use the tools to select a target pH for my water and prep the water to that and probably come up closer in the end on my first recipe and then use a calculator to reverse engineer the changes for the next. Of course the next batch of malt......

 

[ajdelange]

As a general rule a mash of typical grist to liquor ratio might have a buffering capacity of 30 - 50 mEq/kg-pH. Base malts have numbers in the 30's and dark malts higher. Except in unusual cases it is the buffering of that malts that dominates.