Refractometer on soured mash

I'm doing my first sour mash beer, and was wondering if anyone knows of any additional corrections that should me made to a refractometer reading. I was targeting a pre-boil OG of 1.058, but the brix reading converts to 1.068. Either the sour mash made things hyper-efficient, or the lactic acid is throwing off my reading.

Help!

Ok, post-boil on the refractometer is 1.074 for 91% apparent efficiency. This can't be right; it doesn't taste that sweet.

Hey Belmont,

The lactic acid shouldn't have that large of an impact on your readings...might be a slight variance (as anything infused in the liquid will have an effect on the reading). The only thing that I could think of that would throw it off that dramatically would be alcohol - so it's possible a wild yeast got in there and started fermenting? How long did you let it sour mash for? The longer you allowed it to mash, to more efficient it would be (in theory). I'm assuming the refractometer was calibrated - but always worth it to ask/bring up

Hopefully this helps a little. Let me know if you figure it out! Good question by the way...

Cheers!

Jipper said:

The only thing that I could think of that would throw it off that dramatically would be alcohol - so it's possible a wild yeast got in there and started fermenting? How long did you let it sour mash for? The longer you allowed it to mash, to more efficient it would be (in theory). I'm assuming the refractometer was calibrated - but always worth it to ask/bring up

Click to expand...

Thanks! I'm pretty sure I didn't pick up a wild yeast (wouldn't that make my reading too low, rather than too high?) . There wasn't any alcohol flavor, and the sourness was very clean. I soured for about 24 hours, and it probably took a good hour past the 60-minute mash to cool below 145.

I'm a bit lazy, and only calibrate the Zero on my refractometer. Then I use Brewpal's built in conversion factor to get OG from brix.

I guess I'll find out when it's done fermenting. If my FG is 1.020 or higher, I know it's legit.

ps: this fermentation smells pretty funky, in a lip-smacking way. I kind of want to just drink it right now.

Hey Belmont,

The refractometer will read higher than it actually is if there's alcohol. Every year we get a bunch of customers calling during wine season thinking that they have a stuck fermentation at around 3-4 Brix, while they're actually just not compensating for the alcohol (they're actually around 0.996-0.998). It's possible that you just got really good efficiency! Calibrating at zero is all you really should have to do with those, so I guess it's just wait and see time

Hope it turns out well...sounds like the aroma is already there so you're on the right path!

Cheers,
Matt

Just to fill in the final numbers... I tracked fermentation for 7 days, and measured 8.6 brix this morning. Starting at 1.074, that gives an alcohol-corrected final gravity of 1.010. Given how low that is, I would say:

1. The lactic acid doesn't change the refractive index;
2. Sour mashing will boost your efficiency by a huge amount;
3. Sour mashing will increase the fermentability of your wort? Starting at 1.074 and getting down to 1.010 would indicate that most of the worst is very short chain sugars. Tasting it, the beer actually does seem to be light in body, and I get a flavor that I think might be alcohol... It's kind of grapey, like a peeled grape (which is the same smell I get from the Alcohol/Alcool you can buy at the LCBO). The light body is making the sourness come through in a very strong way.

I'm unsure of how this is going to turn out...