Wort acidification AFTER lautering

[TheMerkle]

So, I understand that acidifying sparge water can be tricky when you're using RO because there is very little buffer. This is why I only acidify my mash, and I've seen good results using these methods.
...but what if I want to further acidify my wort AFTER lautering. Anyone know how much lactic 88% it would take to drop 5 gallons of 5.2 ph down to around 4.5? Perhaps I should use a different acid?

 

[mabrungard]

Sparging water needs to have low alkalinity. RO has very low alkalinity and doesn't really need to be acidified.

Mashing water is another thing though. The malt provides a lot of buffering and paler grists often need another source of acid to bring the mash pH down into the preferred range. This is even when your starting water has no alkalinity like distilled water.

 

[Gnomebrewer]

Why would you want a 4.5 boil pH?

 

[ajdelange]

So, I understand that acidifying sparge water can be tricky when you're using RO because there is very little buffer.

It isn't tricky at all. You just need a steady hand. The alkalinity of RO water, that is its proton deficit to target pH pHz is 1000*10^(-pHz). For a reasonable kettle pH of 5.3 that is 1000*10(-5.3) = 0.0050 mEq/L. To acidify 1 gal you would need (3.875*1000*10^-5.3)/11.4 = 0.0017 mL of 88% lactic acid. This is so little that it makes it clear that you do not need to bother with it.

...but what if I want to further acidify my wort AFTER lautering. Anyone know how much lactic 88% it would take to drop 5 gallons of 5.2 ph down to around 4.5? Perhaps I should use a different acid?

Take whatever program you used to determine mash pH and add enough acid to shift the pH estimate down by about 0.1. For example in the Pils I brewed yesterday the estimated mash pH without any acid was 5.407. Adding 200 mEq acid would shift that to 5.317. Thus the sensitivity of this mash to acid addition is about 200/(5.407 - 5.317) = 2222.2 mEq/pH (this mash had 100 lbs of grain). We assume that after the sparge all the soluble stuff, that is, the stuff responsible for the buffering of the mash, is now in the wort and that, therefore, the buffering of the wort is the same as that of the mash. If, therefore, I want to shift the pH of the wort by 0.1 pH I am going to need 0.1*2222.2 = 222.22 mEq of acid. If I want to use lactic acid of 88% strength its normality is 11.4 mEq/mL and I will need 222.22/11.4 = 19.5 mL. So that's how you would calculate the amount of lactic needed based on the assumption. In practice you should take a sample of the wort, add a bit of acid and find the real mEq/pH slope. When I added 20 mL lactic acid to my wort its pH dropped 0.2 to about 5.3 and I finished the boil at 5.1 - mission accomplished. So really you must titrate the wort to see how much acid to add to it for a desired pH just as you must titrate a test mash to see how much acid to add to it. But you can WAG the acid addition with your mash calculator program.

 

[TheMerkle]

Why would you want a 4.5 boil pH?

For kettle souring. This boil pH will encourage my souring wort to stay off the bad nasties and only sourroz as planned.

 

[TheMerkle]

We assume that after the sparge all the soluble stuff, that is, the stuff responsible for the buffering of the mash, is now in the wort and that, therefore, the buffering of the wort is the same as that of the mash.

EXACTLY what I was looking for. Thanks!

 

[ajdelange]

Well that assumption is, based on my experience, a little shaky. Apparently my wort had about half the buffering capacity of the mash. Manfred Moll confirms in Handbook of Brewing (1st ed.) that the buffering of wort is typically about half that of mash (per kg of malt).