hydrometer reading hot wort?

[bernardsmith]

I am still very much learning to brew and last night I made a gallon batch of pale ale working to control mash temperatures and improving my sparging techniques. OK. I took an hydrometer reading shortly after I sparged and the reading was lower than I had expected. I also took a reading shortly after I removed the kettle from the boil but in both cases the temperature of the wort was very significantly higher than the 60 degrees my hydrometer is calibrated to provide a reliable and accurate reading. Does anyone here know what factor I need to add to my readings at temperatures around 3 times the calibrated reading or do I need to chill the sample I am measuring to obtain a good reading? Thanks

 

[Yreval]

I think you should really take a reading around 60 or 65 degrees to get a reliable, meaningful result.

That said, my hydrometer came with a sheet that says you should adjust by:

+.001 70F
+.002 77F
+.003 84F
+.005 95F
+.007 105F
+.008 110F
+.009 113F
+.010 118F

Your mileage here might vary... I'm a bit skeptical of these corrections for my own hydrometer as-is. Any hotter than this and I'd strongly suggest remeasuring at around room temperature.

 

[Genghis]

Either bring your sample down to 60, or plug the numbers into something like http://hbd.org/cgi-bin/recipator/recipator/hydrometer.html

 

[bernardsmith]

Thank you Yreval and Ghengis. I guess I will need to cool the wort in the sample down to 60 degrees. I was simply hoping that there could be a way to measure the gravity "on the fly" so that I could take immediate action if any was needed to correct a problem. And I kinda got a shock last night at the apparently low gravity reading after the boil and thought that the beer I would get would be no where near the 5 percent ABV it should be. But my guess is that the actual gravity is probably far closer to the 1.055 the recipe suggests.

 

[peterj]

You could buy a refractometer. Those are great for taking readings on the fly because they only need a drop or two, which cools down very quickly. You just can't really use them after fermentation begins.

 

[Yreval]

Thank you Yreval and Ghengis. I guess I will need to cool the wort in the sample down to 60 degrees. I was simply hoping that there could be a way to measure the gravity "on the fly" so that I could take immediate action if any was needed to correct a problem. And I kinda got a shock last night at the apparently low gravity reading after the boil and thought that the beer I would get would be no where near the 5 percent ABV it should be. But my guess is that the actual gravity is probably far closer to the 1.055 the recipe suggests.

I understand your desires here.

Luckily, since the amount of liquid you need for a grav reading is relatively small, it's pretty easy and quick to cool down your sample before you measure it. Dunk your vessel in some ice water and you're a couple of minutes away from the temp you want.

 

[IslandLizard]

Cooling samples down is time consuming, so use correction tables or a web calculator. You can create your own tables if needed by calibrating with different temperature water and wort.

For some reason I suspect the temp. corrections to be a percentage of the measured gravity, not absolute numbers.

A refractometer is a good alternative for taking almost instant measurements. It uses such a small amount, 2 drops, the temp has little impact, except.... if very hot, some evaporates before you can close the cover window, giving you inflated readings.

 

[bernardsmith]

I agree that cooling down the sample takes time but on reflection, if I can get my practices up to a level that is both consistent and which reliably produces the kind of results I am looking for then the need to take these readings immediately after sparging and boiling will become less important. In other words, I guess I can live (for the time being) with the idea that I need to take these measurements not so much to enable me to correct an error I have just made but more to assess how good my practice is and whether I need to better control say the mash temperature or modify the volume of strike water I am using given the amount of grains I am mashing or my sparging technique to extract more of the available sugars. So if I can only measure the gravity of the sparged wort when I have cooled a sample to 60 degrees or the gravity of the boil (from a sample) after the boil itself has cooled and after I have pitched the yeast then so be it.

 

[peterj]

It really should only take about 5 minutes to cool down a hydrometer sample. I usually take a pre boil sample after I've mixed my runnings together well and put it in a bowl of ice water while I am heating the kettle up to a boil. It's usually cooled to 60F before my kettle is boiling. Not really much extra effort or any wasted time. Then I take a quick reading and dump it back into the kettle for the boil.

I usually take one after I've chilled the wort too, but as long as you boil off at or around what you were expecting then you won't be far off. The only time you really need a gravity reading is pre boil actually. If you can measure how much you've boiled off then you can accurately calculate what your post boil gravity is. You can do it with formulas or this is a very handy calculator: http://www.brewersfriend.com/dilution-and-boiloff-gravity-calculator/.

 

[bernardsmith]

It really should only take about 5 minutes to cool down a hydrometer sample. I usually take a pre boil sample after I've mixed my runnings together well and put it in a bowl of ice water while I am heating the kettle up to a boil. It's usually cooled to 60F before my kettle is boiling. Not really much extra effort or any wasted time. Then I take a quick reading and dump it back into the kettle for the boil.

...The only time you really need a gravity reading is pre boil actually. If you can measure how much you've boiled off then you can accurately calculate what your post boil gravity is. You can do it with formulas or this is a very handy calculator: http://www.brewersfriend.com/dilution-and-boiloff-gravity-calculator/.

This is very useful indeed, Thanks peterj. I guess I now have to find a quick and easy way to measure the actual volume in my kettle. (a metal ruler with the height converted to volume, perhaps?)

 

[Yooper]

Thank you Yreval and Ghengis. I guess I will need to cool the wort in the sample down to 60 degrees. I was simply hoping that there could be a way to measure the gravity "on the fly" so that I could take immediate action if any was needed to correct a problem. And I kinda got a shock last night at the apparently low gravity reading after the boil and thought that the beer I would get would be no where near the 5 percent ABV it should be. But my guess is that the actual gravity is probably far closer to the 1.055 the recipe suggests.

You can still do it 'on the fly'. You really only have to cool it to under 90 degrees, and then apply the correction formula. Sticking the sample in a skinny pitcher of ice water will do it in just a couple of minutes, and it's easy to do.

Any readings taken over 100 degrees, even with correction tables, are so inaccurate as to be useless. But by cooling it down to 90 degrees or less, the correction tables work just fine.