Calculating the amount of Baking Soda during the boil

[brewjau]

Hi there,

I was wondering if there is a way to calculate the addition of baking soda in the boil to raise the pH of the final wort.

I am asking this because when you brew extreme high-gravity RIS (30-40°P), after long boils, you end up with a low pH (~4.8) considering that you are concentrating a wort with a good amount of roasted and caramel malts.
Is there a way to know how much baking soda to add during the last minutes of boil to try to raise the pH to at least 5.0?

Thanks and Cheers!

 

[Yooper]

0. You don't want to raise the pH in many many cases. If your mash pH and sparge pH are right on, the post-boil pH should be fine. Your pH should drop .15-.3 or so from preboil to post boil so I'd wonder why your pH is so low, and correct it in the mash and sparge.

 

[brewjau]

0. You don't want to raise the pH in many many cases. If your mash pH and sparge pH are right on, the post-boil pH should be fine. Your pH should drop .15-.3 or so from preboil to post boil so I'd wonder why your pH is so low, and correct it in the mash and sparge.

My water is almost absent of ions, and with about 40ppm of HCO3-. I make a series of mashes (usually 2 or 3) always separating the first runnings to the boil kettle, and using the second runnings as the mashing liquor for the next mash. So usually I don't have to correct my mash pH, but I also mash fairly low (~5.2).
My sparge water is always adjusted with lactic acid, ranging from pH 4.3 to 4.5. Since I have to sparge a good amount to have the water necessary for the next mash, I don't want the lauter pH to rise and extract tannins.

 

[cire]

As Yooper has advised.

pH 4.8 is fine for RIS and similar high gravity worts after boiling.

 

[Silver_Is_Money]

I've read a couple peer reviewed documents from commercial brewing past-masters of yore which clearly state that once sparge water alkalinity has been acidified (or via any other means, reduced) down to 50 ppm or less, it will be fine for sparging use (which means that it won't extract tannins). One document even openly expressed that it didn't matter if the waters pH read in the range of 9 as long as its alkalinity as CaCO3 was below 50 ppm.

This one mentions both. See page 327 right column, and then page 328 left column: Brewery Liquor Composition

 

[Silver_Is_Money]

It isn't necessary to reduce sparge water pH to 4.3 (the juncture at which alkalinity hits zero ppm), as adjusting it to 5.4 - 5.6 pH is totally sufficient. But if you are seeing a room temperature measured pH of 4.8 for the mash, you likely needed to be adding baking soda during the mash stage. I've brewed a number of truly robust Stouts, and never hit 4.8 pH. Is that an actual measure, or a software projection?

 

[Silver_Is_Money]

A sufficiently workable 'rule of thumb' is that 1 gram of baking soda neutralizes 1 mL of 88% Lactic Acid.

 

[Silver_Is_Money]

Example of what you are asking:

Givens (g) and presumptions (p):
-------------------------------------------
8 gal Wort at start of boil : (g)
SG = 1.043 at start of boil : (g)
Mash efficiency = 75% : (p)
pH initial = 4.8 : (g)
pH Target = 5.0 : (g)
Grist Buffering Coefficient ~= 45 mEq/Kg.pH for a Congress Mash of your grist at 100% mash efficiency : (p)
Baking Soda's caustic strength at specifically the target pH of 5.0 = 11.4 mEq/gram (g)
36 gravity points per Lb. per gallon for the aggregate grist (p)
Wort buffering scales linearly and 1:1 with mash efficiency (p)

Proposed Method:
------------------------
Inferred Grist Weight = 1000*(1.043-1)*8/(36*0.75) = ~12.741 Lbs.
12.741 Lbs./2.20462 = 5.78 Kg.

Inferred Wort buffering coefficient:
45 mEq/Kg.pH x 0.75 mash efficiency = 33.75 mEq/Kg.pH

Delta_pH = (5.0-4.8) = mEq's/(5.78 Kg x 33.75 mEq/Kg.pH)
mEq's = 39.02 = acid to be removed whereby to move 4.8 pH to 5.0 pH

39.02 mEq's acid/11.4 mEq's/gram of baking soda = 3.42 grams of baking soda to be added

 

[Silver_Is_Money]

7 grams of baking soda would bring the wort pH adjusting example above to 5.2 pH (where baking soda has a strength of 11.12 mEq/mL)

10.9 grams of baking soda would bring the example above to 5.4 pH (where baking soda has a strength of 10.71 mEq/mL)

If your measured 4.8 pH is valid, then somewhere within the vicinity of these two quantities should likely have been added to the mash.

 

[Silver_Is_Money]

Malt Gravity Points per Lb. per Gallon relative equivalence in terms of Malt Gravity Points per Kg. per Decaliter (DL)

46.21: 38.56 (sugar)
38.0 : 31.71
37.5 : 31.30
37.0 : 30.88
36.5 : 30.46
36.0 : 30.04
35.5 : 29.63
35.0 : 29.21
34.5 : 28.79
34.0 : 28.37

1 Decaliter = 10 Liters

Decaliter = Dekaliter = Decalitre = Dekalitre

The meaning of this is such that 1 Kg. of sugar added to 10 Liters of water would be expected to yield a specific gravity (SG) of 1.03856.

For malts, the gravity points "potential" as seen in the data listed above must always be multiplied by the users "mash efficiency" whereby to transition it from a mere potential into an actuality for SG in the real world.

NOTE: I perceive that there is likely to be inherent error in the presumption that 1 Lb. of sugar when added to 1 gallon of water will result in a SG of 1.04621 (or alternately that 1 Kg. of sugar when added to 1 DL of water will yield a SG of 1.03856). The error I perceive comes from an incorrect presumption that after the sugar has been added the volume remains the same. It doesn't. If anyone knows how to rectify and improve the "points" system accordingly, it would be greatly appreciated.

 

[Silver_Is_Money]

I hope that the OP stays around long enough to eventually discover that I've directly answered his/her question within post #8 to this thread. It does not appear that he/she has returned.

 

[mabrungard]

I'm not sure if the horse is already out of the barn on this one. Low mashing pH does reflect into the kettle pH, but there are consequences of low mashing pH that can have an undesirable effect on the beer. The most important one is the creation of excessive proteolysis in the mash that reduces the body of the wort. The beer might be a little thinner bodied because of it.

The other thing low pH effects is the flavor and character of the roast grain contributions. I've not explored if the roast character and flavor can be corrected after a low pH excursion, but its possible. If the beer flavor is sharper than you expect or prefer, you might try adding bits of baking soda to a glass of the beer to see if the flavor improves with subsequent additions. If so, you could scale it up and add to the keg.

A final thing that low pH can do, is reduce the extraction and utilization of hop bittering. So the beer isn't as bittered as you intended.

The bottom line is to target and attain a proper wort pH and carry it through your brewing process.