Yet another low OG thread

[DasBrut]

I am aware of the perpetual issues we have regarding low OG. I read on this board that someone claimed that you can get an abnormally low reading if you pull off the top from an all-grain wort that’s been chilling. Anyone else experience this? I ask because I did an all-grain that read 1.045 (expected 1.06), but it’s been bubbling like gangbusters just like normal, finished at 1.008, and it doesn’t taste like a session.

Next time I will take a reading in the kettle and in the stirred-up primary just before pitching.

 

[Bullhog]

There are many number of reasons why your OG reading could be bad. For instance, if you are using a hydrometer, the hydrometer can stick to the tube and give a false reading. Make sure its freely floating. Tell us a little more about your process.

 

[DasBrut]

Sure, I used a wine thief to take up the wort that was chilling in the kettle. That went into a graduated cylinder. Insert hydrometer, spin. By the time I read it, the temp in the cylinder was 80 F. I should mention there was no top-up.

There are many number of reasons why your OG reading could be bad. For instance, if you are using a hydrometer, the hydrometer can stick to the tube and give a false reading. Make sure its freely floating. Tell us a little more about your process.

 

[Bullhog]

Well that sounds pretty good, my next guess would be you have a different brew house efficiency than used in your recipe calculations. This can happen if you do brew in bag based on a recipe you didn’t write like from a book or magazine.

 

[Bullhog]

I did an all-grain that read 1.045 (expected 1.06),

I used a wine thief to take up the wort that was chilling in the kettle

Another possibility: If you sampled your wort while it was still hot from the kettle, as you mentioned, you could also get a much lower reading if you didn't correct the temperature. Using a hydrometer calculator, 1.045 wort at a temp of 138F is actually 1.060 if your hydrometer was calibrated at 68F. So if your wort was fairly hot, this could be it, or even a combination of lower brewhouse efficiency with taking a reading on warm wort.

 

[BrewnWKopperKat]

[...] you can get an abnormally low reading if you pull off the top from an all-grain wort that’s been chilling.

With my 2.5 gal BIA batches, I measure OG after the mash is complete (before I start heating to a boil) and just before moving the wort into the fermenter. I use a refractometer for these measurements.

On rare occasion, I'll get a noticeably low SG reading for the measurement after the mash is complete. With a short stir, the measured SG will match estimated SG. In all cases, measured post boil SG matches estimated post boil SG.

So my thought is this: if you get a unexpectedly low SG reading, give it stir and measure again.

 

[DasBrut]

Thanks everyone for the advice. I will take several more measurements at different times in my next batch and report back.

 

[DasBrut]

I am here with an update: made an all-grain kolsch and checked the gravity in the kettle during the chill and fermenter with mixing. No real difference, maybe 0.001. So my efficiency is just low and my final gravity is lower than expected. But there are lots of other threads about those issues.

 

[Bobby_M]

While brewers do have some ability to influence extraction efficiency via system process, grain crush, water chemistry, etc... not all of them are mission critical to making a good beer. The biggest issue with "low OG" is in the "supposed to be X.XXX" part. Who is supposing that gravity? The recipe author? All recipes are contingent on a certain brewhouse efficiency if they list the batch size and grain weights.

System Brewhouse Efficiency x grain weight x grain potential / batch size = OG.

The recipe usually has all those items listed (except for the grain potential because that's usually just baked in to the type of malt). Brewing a recipe by carefully weighing out the grain and measuring water volumes but totally ignoring the assumed efficiency is flawed. It's like eyeballing the water amounts or any other such carelessness.

All ranting aside, discover what your typical efficiency numbers are for your system/process and learn to scale the recipe to account for it. Then you won't miss.