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Old 01-31-2010, 05:19 PM   #1
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Default Lactic Acid and Specific Gravity

I recently started playing with sour mashing, My first sour mash I let it run a whole week. When I checked the gravity with my Refractometer It said the SG would be 1.068. I was shooting for about 1.040 so I figure the Lactic acid was contributing to this number.

I fermented the boiled runnings for One week so far, and took a gravity reading using my Hydrometer and It read 1.030. The beer tasted quite sour, but did not have much sweetness. I know I got a good fermentation, because this batch blew off. So I'm assuming that the lactic acid is contributing to the gravity, but how much?

Any one have any good data on Lactic acid and SG? I looked it up and the Chemistry hand book stated that it has a SG of 1.050. But is that a 1M solution?


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Old 02-04-2010, 04:25 AM   #2
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Default Little experiment

So i bought an 88% Lactic acid solution at the LHBS yesterday, and did some measurements.

8.8% lactic acid has a SG of 1.015. This is a lot of Lactic acid way more than what would be in a sour mash so I diluted it down in a solution of 100g/L dextrose and got these #

100g/L dextrose 1.022
100g/L dextrose +8.8% Lactic acid 1.045
100g/L dextrose +4.4% Lactic acid 1.035
100g/L dextrose +2.5% Lactic acid 1.030

50g/L Dextrose +4.4% Lactic acid 1.015

I need to do some math to get a correction factor.


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Old 05-07-2013, 04:58 PM   #3
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So correct me if I am wrong, but it seems like for each 1% of lactic acid the gravity rises by ~2.5 points.
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Old 05-07-2013, 05:06 PM   #4
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88% lactic acid has a density of about 1.206 g/cc at room temperature.
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Old 05-08-2013, 06:40 PM   #5
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Quote:
Originally Posted by ajdelange View Post
88% lactic acid has a density of about 1.206 g/cc at room temperature.
I am not sure what that tells me. What I want to know is if I am growing lacto in some wort and I am monitoring my gravity, how will the gravity change with increases in lacto.
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Old 05-08-2013, 07:03 PM   #6
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Quote:
Originally Posted by ryanhope View Post
I am not sure what that tells me. What I want to know is if I am growing lacto in some wort and I am monitoring my gravity, how will the gravity change with increases in lacto.
Its not a liner relation ship, so its hard to say depending to the % lacto in the beer. I did this before but I can't remember the numbers right now, but I titrated down lactic acid disolved in beer to see what % of lactose was required for the desired level of sourness I was trying to achieve, I'll have to look it up and see if I can find it, but I think it was less than 1-2%.

I plugged these # into excel and made a linier equation

y = -0.0021x + 1.0412 where y is % lactic acid and X is SG.

how to use this??? I don't know for sure. I think the talk home message is that lactic acid will increase your gravity readings.
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Old 05-09-2013, 03:04 AM   #7
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The best way to go about figuring out the attic acid contribution is a titration. That will give you an idea of acid content, but not super accurate because of the complexity of the mixture. Then once you have a round about estimate of acid you can use that to figure the gravity contribution. There may be a kit to specifically courage lactic acid, maybe a yogurt industry based item, or other type acid fermentation QA related kits.


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