Calculating Acid Adjustments

[jrodmfish]

Trying to figure out if I can simplify my process here... I understand that software won't necessarily give me a super accurate mash pH, but it should get me in range. I add my salts and pre-acidify my water before doughing in. Once I dough in, I take a pH reading between 4-5 minutes into the mash.

Here's the question... After, I've done my pH reading, how do I calculate how much acid (lactic 88%) is needed for each unit of pH reduction?

Some data from 3 batches this week:

Batch 1: Coffee Stout
- BeerSmith: estimated mash pH of 5.53 and suggested 3.38ml La88% to get to 5.4pH
- Brewer's Friend: estimated mash pH of 5.54 and suggested 3.33ml La88% to get to 5.4pH

Batch 1: NEIPA
- BeerSmith: estimated mash pH of 5.70 and suggested 8.10ml La88% to get to 5.4pH
- Brewer's Friend: estimated mash pH of 5.68 and suggested 5.47ml La88% to get to 5.4pH

Batch 3: Saison
- BeerSmith: estimated mash pH of 5.75 and suggested 7.3ml La88% to get to 5.4pH
- Brewer's Friend: estimated mash pH of 5.74 and suggested 4.83ml La88% to get to 5.4pH
- Bru'n Water: estimated mash pH of 5.8 and suggested 4.8ml La88% to get to 5.4pH

So all the estimates of mash pH are close, but the acid additions between BeerSmith and Brewer's Friend are way different (Bru'n Water matched BF on the batch I checked it on.) Does anyone know why they nearly match on pH but suggest way different acid additions? And, once I've measured my mash pH, is there a quick calculation to tell me exactly how much lactic acid I should be adding if it's not on target?

 

[ajdelange]

Does anyone know why they nearly match on pH but suggest way different acid additions?

Only in the most general terms and that is that clearly the one program isn't modeling the acidity of lactic acid correctly whereas the other two are.

And, once I've measured my mash pH, is there a quick calculation to tell me exactly how much lactic acid I should be adding if it's not on target?

You shouldn't be in this situation. Do a test mash and the error will be small enough that you can ignore it with a note in your log to use a bit more (or less) next time you brew this beer.

However if you do have an error of magnitude dpH above the target you need to add 50*dpH*m where m is the mass of the grains in kg. This assumes that the buffering of your mash is 50 mEq/kg•pH which it may not be. If it is less than that this formula will tell you to use more acid than you need and you will over shoot so use the amount calculated with 50 but only add 3/4 of it intitially. If after thorough stirring and a wait of a few minutes pH is still too high by enough to concern you then add the last 1/4.

50*dpH*m gives you the required acid in mEq. 88% lactic acid supplies about 11.8 mEq/mL at mash pH.