Gravity Questions ...

I had a low pre boil gravity compared to what it should have been. However, my post boil gravity was actually a tad higher than expected. I can only think it must have something to do with temps. What is the adjustments needed for temp? I took my pre boil gravity at around 125*. My post boil was around 75*.

Several people have said that temperature correction does not work well at temperatures over about 100F. I don't if they're right, but I do know that a refractometer works great. The other thing to consider is how well the wort is mixed before taking the sample. Inadequate mixing can make a very big difference.

-a.

Your gravity reading will be quite a few points lower than accurate when your sample is at 125°F. I'm not sure of the conversion factor to adjust for temp off the top of my head, but I am sure the calculation won't be really accurate at all with that high of an original temperature.

Even 75°F is a tad too warm. Most hydrometers are calibrated for either 60°, 68°, or 70°. Check yours to see what it is calibrated at. And in the future, place your samples in the freezer for a little while to get the temp where it needs to be.

The chart I have says
@125f +.009
@75f +.0015
but like ajf said I too have heard the corrections get wonky the higher you go in temp

That is a good idea. I'll take samples and just hold them aside to get them to room temp before taking readings in the future.

Although when doing all grain, taking readings right out of the mash tun is kind of important. Need to get those readings quickly in order to make gravity adjustments if need be when not getting the expected efficiency.

What to do in that case? Would be nice to have a printed temp conversion chart of somekind handy.

try googling "hydrometer temp conversion chart"

dzlater said:

try googling "hydrometer temp conversion chart"

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Yep, that did it alright. It's even in the Appendix of Palmer's book that I own. Doh!!

It's important to get the sample under 100, even with conversion charts. For the runnings coming out of the MLT, you can either stick the sample jar in the freezer for a few minutes or use an ice water bath to cool the sample. I used to just use a pitcher of ice water, and pop the sample in there. It cooled pretty quickly for a reading. I later bought a refractometer, though!

Is this an extract batch or an all grain batch?

Revvy said:

Is this an extract batch or an all grain batch?

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Neither. PM. Of which I had one hell of a time with. Sparge was stuck almost immediately. Ended up by having to take the mash tun and just dumping through a strainer bag. It was ugly. But I achieved my gravity (with temp adj) and I know exactly why the stuck sparge occured and have already corrected for next time.

Dependent on how long you boil, you need to account for evaporation as well. Evaporation will lead to a concentration of the wort which will, in turn, raise the gravity. If you're not making adjustments based on temperature you aren't getting accurate measurements to begin with though.