a. The target mash pH at room temperature is 5.3-5.8 with a target of 5.5.
Opinions vary here. I'd say 5.2 - 5.6 with 5.4-5.5 the sweet spot. It depends some on the particular beer.
b. Sparge water should be acidified to a room temperature pH of 5.7.
Sparge water should be acidified as necessary to prevent the runoff pH from rising above 6. If the water is low in alkalinity it may not need any acid at all. Clearly, acidifying it to the pH of the mash will more than insure that pH 6 is not exceeded and at the same time minimize the effect of the sparge water on wort pH.
c. Pre-boil ph at room temperature should be in a range of 5.3-5.5 with a target of 5.4.
Pre boil pH will be whatever the mash pH is with some drift. IOW if mash pH is intitially 5.4 it may drift up a bit to say 5.45 or even 5.5 or down a bit to pH 5.35 or so. This depends on whether acids or bases (or acidic or basic malts) have been added to the base malts as the pH establishing reactions can be quite slow.
So, if the mash is around 5.5 and the sparge water is around 5.7. How is the pre-boil pH ever going to get as low as 5.4? Perhaps somebody can help me conceptualize what is going on here.
It isn't. The pH of a mixture will always be between the pH's of the components unless a reaction occurs, such as the reaction between calcium in the water and the phosphates from malt, which releases protons. Thus, as is well known, you can mash a malt with DI pH say 5.7 with hard water at pH 7 and wind up with a mash pH of 5.6. Those reactions take place in the mash and in the kettle.
The general concept is relatively simply explained in terms of the proton deficits and surfeits (negative defecit) of each component in the mash or wort. A proton deficit is the amount of acid (protons) that must be supplied to a mash component to lower its pH from the pH at which it comes to you (its intrinsic pH) to a particular pH of interest, called the reference pH. For example if you have water with alkalinity 100 and pH 7 and wish to use it to obtain a mash pH of 5.4 each liter of that water will need to be treated with 1.79 mEq of acid. That is the proton deficit of the water at pH 5.4: 1.79 mEq/L.
Suppose that you are mashing Crisp Maris Otter. It has a distilled water mash pH (at room temperature) of 5.69. To get a kg of it to pH 5.4 will require 14.07 mEq of acid so its proton deficit at pH 5.4 is 14.08 mEq/kg.
Suppose further that you are mashing 1 kg of the MO in 4 liters of water and want a mash pH of 5.4. The proton deficit for the water is now 4*1.83 = 7.31 and for the malt 14.08 for a total of 21.39. This means that if you make this mash its pH will be higher than 5.4 unless you add 21.39 mEq of acid to it. That acid could come from a bottle of acid or from a colored malt or acidulated malt. Weyermanns acidulated malt has a DI mash pH of 3.6 and will supply 333.8 mEq of protons per kg at pH 5.4. Thus its proton surfeit is 333.8 mEq/kg (deficit -333.8 mEq/kg) to pH 5.4. As you would need 21.39 mEq protons it is clear that you must add 21.39/333.8 = 0.064 kg (64 grams) of sauermalz to the mash to cover the proton deficits of the malt and the water. To sumarize
Water Proton Deficit: 7.31 mEq
Base Malt Proton Deficit: 14.08 mEq
Sauermalz Proton Deficit: -21.39 mEq
Total Proton Deficit: 0 mEq
To further illustrate, let's leave the sauermalz out and compute the proton deficits of the water and base malts at 5.827. These are:
Water Proton Deficit: 6.29 mEq
Base Malt Proton Deficit: -6.29 mEq
Again, the sum is 0. What is happening here is that the base malt is actually acidic with respect to the water and gives up protons to it. The pH of a mixture of 4L of this water with 1 kg of this malt results in a pH of 5.83.
Now lets assume the water is half as alkaline: 50 ppm as CaCO3 and use Munton's Maris Otter with 77 grams of acidulated malt. The numbers at pH 5.4 now look like:
Water Proton Deficit: 3.66 mEq
Base Malt Proton Deficit: 22.07 mEq
Sauermalz Proton Deficit: -25.73 mEq
Total Proton Deficit: 0 mEq
The message here is that the pH of a mixture depends on the proton deficits of each of the components and that the sum of the proton deficits must be 0. This simply says that any protons given off by an acidic component (colored malt, acid, acidualted malt) are absorbed by the basic components (base malts, liquor alkalinity). Some components have more influence than others depending on the component's intrinsic pH, buffering capacity and relative quantity.
