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Refractometer (boiling to measured FG rather than volume)

For those of you who boil down to your starting gravity by measuring with a refractometer, rather than boiling to a calculated finishing volume, how exactly do you go about this process?

In particular I’m interested in how you figure out when to toss in your various finishing hops. Lets say you planned on boiling down to 1.050 and had finishing hops at 15 minutes, 10 minutes, and 5 minutes… How would you know when you were exactly 15 minutes from boiling down to 1.050?

Also, does anybody know why the refractometers with the specific gravity scale never seem to be in stock on any of the major HBS web sites?

You need to know the volume in the kettle and your boiloff rate, at least ballpark, to estimate when to put in the late hops. You can also turn the burner down to just a low simmer at the end to maintain volume if you hit the FG sooner than expected.

A couple minutes after reaching a boil, I pull a wort sample using a syringe and set it aside to cool. While that’s going on, I check the volume (using my high-tech spoon with volume markings on it). Then I take the gravity reading (remembering to account for the sucrose-maltose variation) and calculate the post-boil volume (remembering to account for the wort contraction during chilling). If I’ve hit my numbers, the result for most beers is a 75 min boil, meaning I have about 10 minutes left before the bittering hop addition. The timing of the additions doesn’t change.

Maybe because the SG scale is wrong. Hopefully someone is tooling up to do a new production run with a correct Brix-SG conversion.

Just be sure to allow the wort to chill before placing it on the eye piece. Even though they have ATC, high temps will throw off the calibration.

IME, the reason for alowing the sample to cool is to prevent evaporation. Once it hits the refractometer, it will drop to the temperature of the instrument almost instantly.

The ATC mechanisms in refractometers are calibrated for sucrose solutions anyway. They should always be read at the calibration temperature (20°C, generally) when measuring wort.

Then I take the gravity reading (remembering to account for the sucrose-maltose variation) <<<

Could you explain that or point me towards some good reading on it?

I do have a pretty good handle on my boil off rate but it does seem to vary a surprising amount from brew to brew, which is partly why I want to switch to measuring FG instead of volume.

Maybe because the SG scale is wrong. Hopefully someone is tooling up to do a new production run with a correct Brix-SG conversion.<<<

Serious? Ha ha, if that’s true it would make perfect sense why I haven’t been able to find one, and I’ve been looking off and on for a few months.

Thanks for your help so far everybody!

[quote=“JohnnyB”]>>> Then I take the gravity reading (remembering to account for the sucrose-maltose variation) <<<
Could you explain that or point me towards some good reading on it?[/quote]
Refractometers are designed to measure the gravity of a sucrose solution (i.e. wine must). To account for the sugars present in wort (mostly maltose) you have to apply a correction. It’ll be different for each wort, but generally brewers divide the reading by 1.04, which should get you within 1% or so.

Thanks! Glad I didn’t start using one before knowing that.

And remember that once you pitch yeast, you have to apply a correction factor to any refractometer reading in order to account for the presence of alcohol in the beer.

Ya, I had heard of that. My plan for now is to continue to use my hydrometer once fermentation starts.

You can check your gravity any time during fermentation just by dipping a sanitized metal skewer into the beer and letting one or two drops fall on the refractometer window - much easier and faster than using a hydrometer.

Like this one? :mrgreen:

http://seanterrill.com/2011/04/07/refra ... g-results/

Pre fermentation I have been quite close just taking the brix reading x4.

10.0 Brix= 1.040

In light of the info learned in this thread, I’ve gone ahead and finally ordered a refractometer with the brix scale rather than waiting for the (possibly) incorrect SG scale models to come back in stock.

Merry xmas to me, and thanks for all thoughts in the thread. I’m looking forward to putting my hydrometers into retirement!

[quote=“a10t2”]Like this one? :mrgreen:

http://seanterrill.com/2011/04/07/refra ... g-results/[/quote]

Sean, thanks for this spreadsheet by the way. I use it all the time now and really like it! Now if we could just get your equations built into BeerSmith then life would be sweet…

It just depends on how much accuracy you want/need. 10°P is 1.040, 20°P is 1.083, 30°P is 1.130, and so on. If you only brew average-gravity beers then multiplying by four might be good enough.

I’m glad you find it useful. If any developers were interested in incorporating it, we could certainly make that happen.

[quote=“a10t2”]
I’m glad you find it useful. If any developers were interested in incorporating it, we could certainly make that happen.[/quote]

I’m actually considering developing a free web based suite of brewing tools in order to gain the experience, and also to demonstrate my skills to potential employers. If I decide to go ahead with this, can I contact you about including your calculations?

If you’re interested, I could also develop something for you using javascript so that you could host a web based calculator on your own site.

[quote=“JohnnyB”]I’m actually considering developing a free web based suite of brewing tools in order to gain the experience, and also to demonstrate my skills to potential employers. If I decide to go ahead with this, can I contact you about including your calculations?

If you’re interested, I could also develop something for you using javascript so that you could host a web based calculator on your own site.[/quote]
Feel free to include it. Everything on the site is under a CC license and free for non-commercial use. Just let me know.

The JS calculator is something that’s going to be happening soon. I just haven’t had the time recently.

Great. Thank you!

Thanks for the kick in the pants. I finally got the JS calculator written. (Well, PHP technically, which is slow but easier to implement in WordPress.)

http://seanterrill.com/2012/01/06/refra ... alculator/
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