The general back of the napkin formula is:

Delta_pH = mEq's/(BC x Kg)

Where:

BC = buffering capacity, in units of mEq/Kg_pH

Kg = Kilograms of grist being mashed

Delta_pH = pH_Initial - pH_Target

mEq's = the number of milliequivalents of acid or base required to move the pH to the target.

Some short cuts are in order here, since this is the back of the napkin, or down and dirty method, and foremost is a presumption that quite often BC ~= 35

The real trick is in determining a recipe grists initial pH condition, and Alkalinity, volume of mash water at said alkalinity, mineralization, and each grist components pHDI (pH in deionized water) all interact here, but we will skip the hard stuff and make more presumptions here. Lets presume that our aggregate grist is mashing in RO water, and therefore Alkalinity is near zip. Lets also presume low calcium and magnesium levels, whereby we can downplay (their generally overplayed) impact upon downward pH shift.

On to an example:

Givens for the example:

BC = 35

Kg_Grist = 5.25

Initial pre adjustment mash pH = 5.72

Target mash pH = 5.40

88% Lactic Acids relative strength at pH 5.40 = 11.451 mEq/mL

Lets go:

Delta_pH = mEq's/(BC x Kg)

(5.72-5.40) = mEq's/(35 x 5.25)

0.32 = mEq's/183.75

183.75 x 0.32 = mEq's

mEq's = 58.8

58.8 mEq/11.451 mEq/mL = 5.1 mL of 88% Lactic Acid

Answer = Add 5.1 mL of 88% Lactic Acid whereby to bring the pH of the mash to 5.40

Delta_pH = mEq's/(BC x Kg)

Where:

BC = buffering capacity, in units of mEq/Kg_pH

Kg = Kilograms of grist being mashed

Delta_pH = pH_Initial - pH_Target

mEq's = the number of milliequivalents of acid or base required to move the pH to the target.

Some short cuts are in order here, since this is the back of the napkin, or down and dirty method, and foremost is a presumption that quite often BC ~= 35

The real trick is in determining a recipe grists initial pH condition, and Alkalinity, volume of mash water at said alkalinity, mineralization, and each grist components pHDI (pH in deionized water) all interact here, but we will skip the hard stuff and make more presumptions here. Lets presume that our aggregate grist is mashing in RO water, and therefore Alkalinity is near zip. Lets also presume low calcium and magnesium levels, whereby we can downplay (their generally overplayed) impact upon downward pH shift.

On to an example:

Givens for the example:

BC = 35

Kg_Grist = 5.25

Initial pre adjustment mash pH = 5.72

Target mash pH = 5.40

88% Lactic Acids relative strength at pH 5.40 = 11.451 mEq/mL

Lets go:

Delta_pH = mEq's/(BC x Kg)

(5.72-5.40) = mEq's/(35 x 5.25)

0.32 = mEq's/183.75

183.75 x 0.32 = mEq's

mEq's = 58.8

58.8 mEq/11.451 mEq/mL = 5.1 mL of 88% Lactic Acid

Answer = Add 5.1 mL of 88% Lactic Acid whereby to bring the pH of the mash to 5.40

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