Test mash that examines the effect of strike pH on mash pH

[premington]

This post relates to a previous thread that discussed whether it was necessary and/or beneficial to adjust strike water pH prior to dough-in. Some feel that adjusting pH is not necessary while others believe it can benefit the mash pH.

I wanted to learn what would happen if I adjusted the strike water pH. I'll be making an American Ale in a week, so I used this recipe's grain bill. This will help decide on adjustments to the strike and sparge water.

I just finished performing four test mashes. The results were interesting. It turned out a little different than I thought.

Here's the grain bill for the American ale. All amounts have been reduced 1/100th of the amount used in the recipe.

Water: 4 gallons are used in the initial mash (not counting sparge). Amount in each sample: 5.12 oz.

2-row (1.8L): 35.84 g (recipe amount: 8 lbs.)
Vienna malt: 6.72 g (recipe amount: 1.5 lbs.)
Crystal 20L: 4.48 g (recipe amount: 1 lb.)
Flaked rice: 4.48 g (recipe amount: 1 lb.)
Flaked wheat: 2.24 g (recipe amount: .5 lbs.)

Four test strike water samples were prepared. Three samples were treated with Lactic acid.

Strike 1: 7.5 pH (untreated out of filtered tap)
Strike 2: 6.2 pH
Strike 3: 5.8 pH
Strike 4: 5.4 pH

I was not able to adjust the water ion concentration to what I intend to use in the recipe. The additions were so miniscule when reduced to a 1 gallon batch, I wasn't able to measure the amount on my digital scale. Additions would have been a very small amount of calcium chloride and gypsum.

The grains were added with water temp at 158 F. A few minutes after strike, the temperature stabilized to about 156 F. I let it drop to 154 F, then added each vessel back to preheated water, which held this temperature for 20 minutes (+/- 1 F).

After 20 minutes, I gave the samples a brief stir and then measured the pH of each. The pH test meter has automatic temperature compensation (ATC). Each sample's temperature was ~154 F.

The results are as follows:

Sample 1 Water pH: 7.5...... Mash pH: 5.65
Sample 2 Water pH: 6.2...... Mash pH: 5.6
Sample 3 Water pH: 5.8...... Mash pH: 5.57
Sample 4 Water pH: 5.4...... Mash pH: 5.57

So this little mash test showed a negligible difference in the mash pH when the strike water is treated prior to dough-in. Adjusting the strike water pH did result in a difference to mash pH, but the change was less than .1. Once the strike water reached 6.2, the change in mash pH was .05. Lower than 6.0 resulted in no mash pH change. Both the 5.8 and 5.4 samples settled out at 5.57.

What I find interesting is, the 5.4 sample increased pH to 5.57 while the 5.8 pH sample decreased to 5.57. I didn't think I'd see the mash pH raise. it appears the mash pH settles out on its own, even when doing so results in an increase in pH compared to the strike water pH.

It appears those who state it's not necessary to adjust pH prior to dough-in are somewhat correct. It doesn't appear to make too much difference with this grain bill. That stated, I'm personally not comfortable pitching water that has pH of well over 6.0. Based on these results, I'm inclined to set the strike pH to around 5.8, without being concerned for small variances.

Please post your thoughts. There are a lot of knowledgeable people here, and I'm interested to hear what others think.

 

[ajdelange]

Some things noted in the earlier thread were that

1) The effect of acidifying your water to mash pH depends on the alkalinity of the water, If it is appreciably less than the alkalinity of the grist then acidifying to mash pH prior to strike will have little effect on final mash pH.

2) Once strike water pH is less than 6 we are coming on to the flat part of the titration curve and a further decrease in strike water pH will have less of an effect on mash pH than an equal sized drop in strike water pH above 6.

These data seem to support both of these points. We would assume from them that your water is not terribly alkaline. A check of the other thread confirms this. You report alkalinity of 1.3 mEq/L (65 ppm as CaCO3) which is only 0.3 above the nominal 1 mEq/L level above which we start to worry about alkalinity.

 

[Silver_Is_Money]

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[ScrewyBrewer]

The accuracy of your pH readings can be improved when both the solutions used to calibrate the meter and the pH samples are at room temperature. The 'same temperature' approach also applies to meters with built in Automatic Temperature Compensation (ATC) and Automatic Buffer Recognition (ABR).

Without diving too deeply into the Nernst Equation and pH electrode response. There are several sources of error to consider when evaluating the accuracy of pH measurements. Including calibration isopotential point, thermal or chemical equilibrium effects on the electrode and the temperature coefficient of variation on buffers and samples. Reducing potential sources of measurement error, related to temperature, can be achieved by meter calibration and sample measurement taken at the same temperature.

Obviously calibrating a pH meter and taking pH samples that are at room temperature will greatly extend the useful life of the pH electrode. But there are plenty of other compelling reasons to do so. One interesting treatment of the subject can be found at The Effects of Temperature on pH Measurement by John J. Barron Colin Ashton & Leo Geary.

 

[rayg]

The reason the pH of the mash doesn't change much regardless of the strike water pH is that the resulting mash is a buffer system with a pretty high buffering capacity, and your highest initial pH was not too high. A few more tests at pH 8, 9 and 10 would be interesting. But I think you've demonstrated that pH adjustments aren't necessary for most waters. But even if the pH isn't "optimal", it's hardly likely that a pH of say 5.7 versus 5.3 would be noticed by a homebrewer, because you are talking about a few percent in conversion for exactly the same mash time and temperature, and you can adjust those if you really feel it's necessary. It can't have an effect on flavor because the fermentation drives the pH to between 4.5 and 3.8 depending on the yeast strain (probably even lower for sour beers).Sometimes a technique that is valid for extreme conditions, such as the combination of high pH water with under modified malt combined with a big brewery's need to get every last percent of extract for financial reasons gets co-opted as a necessity for everyone, when it is not.

Ray

 

[ajdelange]

The accuracy of your pH readings can be improved when both the solutions used to calibrate the meter and the pH samples are at room temperature. The 'same temperature' approach also applies to meters with built in Automatic Temperature Compensation (ATC) and Automatic Buffer Recognition (ABR).

Yes, the best accuracy is obtained if both buffers and sample are at the same temperature when the isoelectric pH of the electrode is substantially different from 7 but modern technology insures that it usually is within ± 1 pH (though I have an old electrode with pHi = 8.5) and measurements are pretty insensitive to this which is why the tolerance band is so wide. The relevant equations are at https://www.homebrewtalk.com/showthread.php?t=302256.

For the most accurate work I calibrate at several buffer temperatures and am thus able to determine slope, offset and isoelectric pH and use them in the equations I referenced to calculate pH from the electrode's mV response but I do not do this when brewing or in general - only when I'm collecting data for a paper or book as it is not usually necessary. Plug a few numbers into the equations and see for yourself. Remember that the buffers we use are usually rated ±0.02 pH and I doubt pHi error within the ±1 pH band would garner you that much error until Tcal and Tsamp got pretty far apart.

The NIST traceable buffers we buy are standardized so they change temperature in the same way (within tolerance) from manufacturer to manufacturer. Your meter has the tables in it ROM.

 

[ajdelange]

The reason the pH of the mash doesn't change much regardless of the strike water pH is that the resulting mash is a buffer system with a pretty high buffering capacity, and your highest initial pH was not too high.

The reason the pH doesn't change much is, as I said in #2, because the water has little buffering capacity, 17.5mEq for a mash using 4 gal of OP's water as opposed to the buffering of the malts 41 mEq (again for the whole mash) for a grist similar to what OP proposes WRT mash pH 5.5. Were the alkalinity of the water 130 (twice what he had reported) then the result would be quite different and more dramatic.

A few more tests at pH 8, 9 and 10 would be interesting.

His water comes in at pH 7.7 with alkalinity 65. To get it to pH 8, 9 or 10 he'd have to add alkali which would obviously raise the mash ph but that is obvious and thus not very interesting.

But I think you've demonstrated that pH adjustments aren't necessary for most waters.

Only if most waters have alkalinity near 1 mEq/L which, as i mentioned in #2 is sort of the upper limit with respect to brewers being comfortable.

Actually, of course, you don't have to adjust the pH of your strike water at all provided you add the acid required to neutralize its alkalinity somewhere else. The value in setting strike water pH is that it is, in effect, a titration which determines the alkalinity of the water and compensates for any termporal variation automatically.

But even if the pH isn't "optimal", it's hardly likely that a pH of say 5.7 versus 5.3 would be noticed by a homebrewer, because you are talking about a few percent in conversion for exactly the same mash time and temperature, and you can adjust those if you really feel it's necessary. It can't have an effect on flavor because the fermentation drives the pH to between 4.5 and 3.8 depending on the yeast strain (probably even lower for sour beers).

But it does indeed have a profound effect on flavor with most, when they first undertake mash pH control reporting something like "all the flavors seem brighter" or "it's as if someone turned the lights on". What the yeast do depends on what you present them to work with.

 

[BigGutHeavyD]

Thanks for taking the time to do this.

What is the difference between adjusting strike water pH and adjusting mash pH? How would you determine what strike water pH is needed without accounting for the grains? Are you implying that if one adjusts strike water pH that the mash pH will take care of itself and we no longer need mash pH calculators?

If you perform the test again, record what a mash pH calculator (EZ water, Brun'Water, etc...) says the strike water pH should be at for each of your target pH levels.

What about with Distilled water vs. High Alkalinity water?

Very interesting to be sure, but with a strike water only adjustment how would one answer the question, "How do I arrive at a mash pH of 5.4 without accounting for the grain acidity and buffering (i.e. without knowing anything about the grain)?"

 

[ajdelange]

What is the difference between adjusting strike water pH and adjusting mash pH?

Nothing except convenience. You can add the acid for the water to the mash if you prefer. As stated in the previous post the big advantage is that you don't need to know the water's alkalinity if you adjust its pH. In so doing you zero the alkalinity WRT mash pH without having to know what it is. If you account for it otherwise you must know or measure the alkalinity each time. Some people are fortunate and have pretty constant alkalinity over time. For others it can vary appreciably.

How would you determine what strike water pH is needed without accounting for the grains?

The required strike water pH is the desired mash pH.

Are you implying that if one adjusts strike water pH that the mash pH will take care of itself and we no longer need mash pH calculators?

No. There are two parts to determining the acid requirement. The first is to determine the amount of acid necessary to neutralize the alkalinity of the water. The second is to determine the amount of acid necessary to neutralize the alkalinity in the malts. Setting strike water automatically takes care of part 1. You must still do part 2. To do part 2 in a spreadsheet just tell it that your water's alkalinity is 0.

What about with Distilled water vs. High Alkalinity water?

Distilled water is already adjusted. It takes so little acid to set distilled water to mash pH that we simply assume it is already at mash pH. It's effective alkalinity is practically speaking 0. With high alkalinity water you will need to add more acid than with moderate or low alkalinity water. Again, the amount of acid is correctly determined when the target mash pH is reached whatever the alkalinity level of the water. You should, however, think about the acid anion whose concentration will be quite high if the source water's alkalinity is high.

with a strike water only adjustment how would one answer the question, "How do I arrive at a mash pH of 5.4 without accounting for the grain acidity and buffering (i.e. without knowing anything about the grain)?"

You don't. You must still calculate the acid required for the grains. Do this by entering them into a spreadsheet with the water's alkalinity set to 0.

This will work with a spreadsheet that properly models alkalinity. I suspect several of them don't.

 

[ScrewyBrewer]

The reason the pH of the mash doesn't change much regardless of the strike water pH is that the resulting mash is a buffer system with a pretty high buffering capacity, and your highest initial pH was not too high.

The DI pH of the combined grains being mashed, has a greater influence on the overall mash pH when the strike water has low alkalinity. The pH of low alkalinity strike water is easily changed when coming into contact with the grain in the mash.

When carbon dioxide in the atmosphere, interacts with low alkalinity water, the carbonic acid (H2CO3) that is formed is enough to lower the pH of the water. How much lower the pH changes is completely dependent on water alkalinity. Conversely, water with higher alkalinity will be more resistant to pH changes. Optimally, the strike water buffers are strongest when within range of the target mash pH value, (This requires having the correct DI pH values for the grain used.)

When a brewing water profile calls for a target mash pH of 5.3, the strike water can be treated ahead of time, so that when it is mixed with the grain the pH of the mash comes very close to 5.3. The combination of strike water pH and alkalinity creates a buffer that resists pH changes introduced by the grain in the mash.

 

[ajdelange]

The DI pH of the combined grains being mashed, has a greater influence on the overall mash pH when the strike water has low alkalinity. The pH of low alkalinity strike water is easily changed when coming into contact with the grain in the mash.

Yes

When carbon dioxide in the atmosphere, interacts with low alkalinity water, the carbonic acid (H2CO3) that is formed is enough to lower the pH of the water. How much lower the pH changes is completely dependent on water alkalinity.

When this happens the amount of CO2 that dissolves is miniscule and even DI water's pH doesn't shift much (to pH 5.6 if PaCO2 is 0.0003 Atm.) and the alkalinity of such water is actually less than that of pure water (about 2 mEq/L) because of the low pH. IOW atmospheric CO2 has little to do with this.

Optimally, the strike water buffers are strongest when within range of the target mash pH value

The strike water buffer (bicarbonate) is strongest when near pH 6.38 (the first pK of carbonic acid). By the time we approach mash pH we are getting onto the flat part of the titration curve, most of the bicarbonate has left the solution as CO2 gas and buffering is minimal (from the water - it's all the grains at this point). That's why mash pH doesn't change much between strike water pH of say 5.5 and 5.6.

When a brewing water profile calls for a target mash pH of 5.3, the strike water can be treated ahead of time, so that when it is mixed with the grain the pH of the mash comes very close to 5.3. The combination of strike water pH and alkalinity creates a buffer that resists pH changes introduced by the grain in the mash.

When strike water is acidified to mash pH its effective alkalinity is 0 so that it is the grains alone that set the pH.

 

[BigGutHeavyD]

What are the benefits to this two step process?

1. Acidify strike water to mash pH
2. After dough in - further acidify mash to reach mash pH (this shouldn't be necessary (due to step 1) if water with no or low alkalinity is used?)

As opposed to:

1.) Acidify strike water such that after dough in the resulting mash reaches mash pH

This sounds like it would mainly be useful for strike water that has a moderate to high degree of alkalinity?

 

[ajdelange]

What are the benefits to this two step process?

1. Acidify strike water to mash pH

As has been stated several times before the main benefit, IMO, is that one does not have to measure the alkalinity of the water each time he brews and do a calculation as to the amount of acid he needs to overcome the water's alkalinity. That is all taken care of automatically.

2. After dough in - further acidify mash to reach mash pH (this shouldn't be necessary (due to step 1) if water with no or low alkalinity is used?)

This is still necessary as acidifying the water only accounts for the water's alkalinity. Whether the water be heavily alkaline or no the malts' alkalinities still have to be calculated and acid for that added to the mash. Of course that acid can be added to the mash water too.

As opposed to:

1.) Acidify strike water such that after dough in the resulting mash reaches mash pH

To do it this way requires that the water alkalinity be measured each time (unless you know it to be temporally stable) and a calculation done for the amount of acid required to neutralize it AND that the same thing be done for the malts.

This sounds like it would mainly be useful for strike water that has a moderate to high degree of alkalinity?

If the water is low in alkalinity this is the easier method as low alkalinity water does not require acid.

 

[ScrewyBrewer]

When strike water is acidified to mash pH its effective alkalinity is 0 so that it is the grains alone that set the pH.

Except in a real world scenario where brewing salts and acid are added (think flavoring) directly to the strike water. The addition of calcium, chloride and/or magnesium, in sufficient amounts to RO water, can increase the alkalinity caused by bicarbonate to the point where not all of it is eliminated by the acid. The amount of acid neutralized is less than the final adjusted acid.

 

[ajdelange]

It is important to understand that at mash pH most of the bicarbonate has been removed. That is why we add acid. It is also important to understand that neither calcium, magnesium nor chloride increase the alkalinity of any bicarbonate which remains. Quite the opposite in the case of calcium and magnesium which react with malt phosphate to release protons thus decreasing the alkalinity of the mash. But they must be in the mash. In the water alone they have no pH modulating effect.

But you are quite right to point out that it isn't the grains alone that are responsible for setting mash pH once the water is acidified. Other things added to the grains such as acids, bases, calcium and magnesium also do.