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Old 01-03-2013, 11:45 PM   #1
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Default Lactic Acid Use?

Is there some sort of idea how much lactic acid brings down wort pH?

For instance.. let's say I have to bring the pH down from 6.2 to 5.2 and I'm brewing 5 gallons of beer in the fermenter?

Is it more complicated than that? I'm really looking for an IDEA to get me in the ball park. I don't want to add too much and try to correct. Even if I can say, use x number of 1/4 tsps to do the major drop.. then add a little more as needed.

The LA I have is 88%

The same question holds true for phosphoric acid. I don't have any of that yet.. and I'm sure what my LHBS carries is not very strong. I think it's 25%.

I'm guessing phosphoric might be better to add for an APA vs LAcid due to add changes in flavor???

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Old 01-03-2013, 11:48 PM   #2
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It's actually more driven by the amount of grain than the gallons of wort.

Here is what I figured out:
http://woodlandbrew.blogspot.com/2012/10/mash-ph.html

I've heard that lactic acid has flavor, but I've never had a problem with it. I don't think the 1/4 tsp that I typically add can be tasted in a five gallon batch.

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Old 01-03-2013, 11:57 PM   #3
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Quote:
Originally Posted by ThreeGnomes View Post
Is there some sort of idea how much lactic acid brings down wort pH?

For instance.. let's say I have to bring the pH down from 6.2 to 5.2 and I'm brewing 5 gallons of beer in the fermenter?

Is it more complicated than that? I'm really looking for an IDEA to get me in the ball park. I don't want to add too much and try to correct. Even if I can say, use x number of 1/4 tsps to do the major drop.. then add a little more as needed.

The LA I have is 88%

The same question holds true for phosphoric acid. I don't have any of that yet.. and I'm sure what my LHBS carries is not very strong. I think it's 25%.

I'm guessing phosphoric might be better to add for an APA vs LAcid due to add changes in flavor???
The Bru 'n Water spreadsheet will let you enter your acid type and strength and will do all the calculations for you based on your grain bill.
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Old 01-04-2013, 03:41 AM   #4
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There is a rule of thumb that says that each 1% of total grist weight of sauermalz will bring mash pH down by about 0.1 pH. This comes from Weyermann's web site, has been accurate in my experience and I have never seen anyone question or challenge it. Given that sauermalz is, on average, 2% lactic acid by weight you can easily calculate the equivalent amount of lactic acid by weight. To get volume note that 88% lactic acid weighs 1.206 grams/cc.

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Old 01-04-2013, 04:32 AM   #5
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Well, unfortunately.. my question starts from a competition we are in on Sunday.. It's called Iron Brew.. We only know two things. The batch size (5 G) and the Yeast (WLP001) We have no idea what the grains are and we don't know the hops. We can weigh the grain.. Be nice to know more

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Old 01-04-2013, 11:07 AM   #6
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ml of lactic acid = change in pH * weight of grains in lbs.

If you want to play it safe use half as much as the equation recommends and measure again.

Best of luck in the competition.

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Old 01-04-2013, 12:28 PM   #7
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Quote:
Originally Posted by ThreeGnomes View Post
Well, unfortunately.. my question starts from a competition we are in on Sunday.. It's called Iron Brew.. We only know two things. The batch size (5 G) and the Yeast (WLP001) We have no idea what the grains are and we don't know the hops. We can weigh the grain.. Be nice to know more
It doesn't matter what the grains are in terms of the rule of thumb. Of course in actuality it does but the rule of thumb assumes that the buffering capacity of most grists is about the same. The fact that it varies somewhat is why the rule of thumb is a rule of thumb and not much more. The amount you need also depends on the pH of the mash without the addition of lactic acid/sauermalz. If it is 5.7 and you want 5.4 then you would add 3% sauermalz or the equivalent amount of lactic acid. If it is 5.2 then you would add -2% i.e. alkali with the equivalent strength of the lactic acid in 2% sauermalz.

I didn't work out the equivalent acid for a pound of sauermalz because I try to force people to do a little thinking for themselves but the rest of the story is that pound of sauermalz weighs 454 grams and at 2% lactic acid that implies each pound contains 0.02*454 = 9.08 grams. Thus if your mash pH comes in at 5.65 without acid and you want 5.4 that would require 2.5% sauermalz. Assuming 10 pounds of grain you would need 0.25 lbs sauermalz equivalent to 0.25*9.08 = 2.27 grams of lactic acid. If you are using 88% lactic acid solution you would need 2.27/0.88 = 2.58 grams of the solution. As the density of an 88% solution is 1.206 grams/mL that's 2.58/1.206= 2.14 mL. Putting it all together in one formula

mL_88%Lactic = ((pH_w/o_acid - desired_pH)*10/100))*weight_of_grain*454*.02/.88/1.206

mL_88%Lactic = 0.86*(pH_w/o_acid - desired_pH)*weight_of_grain

Obviously it would be best to use a good pH meter to measure the pH w/o the lactic acid and then make the adjustment based on what you measure. Barring that then you would have to WAG based on what you know about the beer and the water. Given that you are using WLP001 we can assume it is an ale. For a pale ale 2% sauermalz is a good guess if the water is of moderate carbonate level. If the water is low in carbonate you might want to decrease that and if the water is higher increase it. As the amount of crystal malt increases the amount of sauermalz/lactic acid should decrease. For stouts don't use any.
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Old 01-04-2013, 01:42 PM   #8
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I have done quite amount of work on this.

First off, are we talking about wort, mash or beer? That's important b/c there is a big difference in buffer capacity. ThreeGnomes seems to talk about beer in the fermenter.

I have done titration tests on mash, beer and wort and the results are here:

http://braukaiser.com/blog/blog/2010/11/29/mash-titration/
http://braukaiser.com/blog/blog/2010/11/25/wort-and-beer-titration/

For beer I found a slope of around 90 mEq/(kg*pH) (pH doesn't really have a unit but making it a unit better documents the buffer capacity). That buffer capacity is per kg or original extract and to give an estimate for lactic acid needed I would need the OG of the beer.

But how did you end up with a wort pH of 6.2? You mash pH must have been even higher than that.

Kai

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Old 01-04-2013, 01:52 PM   #9
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Good point Kai,

The rule of thumb I provided is for correcting the pH of the mash after dough in. Pre-fermentation wort pH is not something I have explored.

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Old 01-04-2013, 03:05 PM   #10
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Of course in actuality it does but the rule of thumb assumes that the buffering capacity of most grists is about the same.
I meant to indicate what that buffering capacity is but forgot to do it.

1 kg malt
1% sauermalz --> 0.1 pH shift
1% of 1 kg = 10 grams sauermalz
2% lactic acid in 10 grams --> 200 mg.
Equivalent weight of lactic acid at pH 5.4: 93.0
Equivalent weight of lactic acid at pH 5.5: 92.4
200 mg lactic acid yields 200/93 = 2.15 mEq
Buffering capacity of rule of thumb grist: 2.15/.1/1 = 21.5 mEq/kg-pH

Of the handful of malts I've actually measured the average first order buffering term (i.e. the buffering at the DI mash pH) has been 26.2 mEq/kg-pH with standard deviation 8.5. Thus the Wyermann rule of thumb is within one standard deviation of the average buffering capacity I've found. Interesting.
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