Is There Any Way to Back Calculate OG from Finished Beer?

[Fat Bastard]

Strange Question: I've had a run of beers finishing higher than expected, and have reason to suspect there is something funny going on with my post boil refractometer readings. They seem to be quite a bit higher than expected, and this is impacting on my gravity readings from the fermenter. Refractometer readings taken pre-boil seem fine. I suspect my Refrac is very sensitive to suspended material in the wort and that's what the issue is there. I'm getting fuzzy lines, higher than expected readings that would indicate massive boil off rates, but that's not actually happening.

I own a hydrometer, but it's probably lying smashed in the bottom of a box somewhere.

Is there any way to calculate the alcohol content of finished beer without measuring the gravity? Can I boil off the alcohol from a sample and compare the weights before and after? I do own a set of very accurate scales. Well ones that go down to .01g anyway.

I'd appreciate your thoughts!

Cheers!

FB

 

[bum]

If you think your pre-boil is accurate and you've got your system dialed in so that your boil off is fairly predictable then you should be able to guestimate it fairly closely.

What's your end-game here? Working out if your refractometer is actually out? Find that hydrometer. Much less pfaffing about - the down side is that you'll have to make beer. The things we do for science!

 

[Fat Bastard]

Mostly to see if the refrac needs chucking out. The last brew was a IIPA I've done 7 or so times previously, but I altered a few things this time, small stuff like using a little acidulated malt and using candi syrup instead of dex. I just want to be sure that's not giving me 1.085 instead of the expected 1.075.

I graph my grain bill, efficiency and apparent attenuation, so I know something is going on in the last few brews compared to the last 20 or so. Just need to work out what it is!

 

[bum]

Not a very sciencey question, but I assume you're adjusting your hopping to account for the extra 10 points - are they drinking as they should be or are they more bitter than you'd expect?

 

[pk.sax]

Different batch of grain fb? Water additions? Re circulation or stirring? Different milling? Getting used to your equipment?

 

[Greg.L]

You can use an ebulliometer to work out alcohol content via change in boiling point. Pricey bits of equipment but there are sometimes cheap ones on ebay.

 

[treefiddy]

Make a 10 brix solution (10 g sucrose, 90 g water). Check this against your refrac.
Take refrac reading of your beer.
Take hydro reading of your beer.

Use this calculator: http://brew.stderr.net/refractometer.html

 

[mkstalen]

5 Ways to determine Alc%

1. Density and Refractive Index method
2. Distillation followed by hydrometry/refractometry method
3. Ebulliometer method
4. Gas chromatography (GC) method
5. Spectroscopy (infra red) method

http://www.winegrowers.info/wine_making/Alcohol.

You've tried method 1. I'm guessing methods 3, 4 & 5 are probably out of your league. Leaving Method 2 left to try.

 

[mmmyummybeer]

Yes you can but you are far better off trying to work out your hydrometer issues. I find suspended material does make a difference to my refract reading hence I take a sample of the top after settling.

Just for interest - Working out alcohol content without a starting gravity would require an alcohol distillation unit where you take 100ml sample add 100ml distilled water into a 1000ml flask. Distil until you get nearly 100ml distillate into a 100ml flask then top up to 100ml. You will then need an alcohol hydrometer that is design pacifically for alcohol and will tell you the alcohol content when measured at 20C. This method is considered more accurate than gravity reading because it eliminated all suspended particles but as you would be gathering by now its not cheap when you have to buy the distillation unit, lab flasks and alcohol hydrometer(which are generally dearer than gravity ones).

Another interesting fact is that you can actually work out OG if you have an alcohol measurement. If you buy a bottle of beer, it will always states the alcohol content, you can just degas the beer take a gravity reading which will be a FG then you can use this to calculate the OG, some people find this handy for replicating their favorite beers.

Any way that's my 2cent and more than enough rambling. Good luck with your refract.

Edit - Ops of course any of the methods Steinberg mentioned. Have scene spectroscopy work too, amazing stuff but lots of money and takes lots of calibrating with reference samples. It even works with out taking the beer out of its container. Just shines a beam of light varying through the sample in the near infa red wavelengths and then measuring its absorption and refraction.

 

[Fat Bastard]

Hmmm. This is all a bit science-y. I might go and annoy the chemists at work to see if we have anything that might help me.
I haven't changed my process, even the grain was from the same bag! Haven't tried to correct the bitterness, as the fermenter samples taste as they should. In any case it's a bit of a hop monster @ 106 IBU and 600 odd grams in a 23 litre batch. If I can borrow an alcohol hydrometer from the pointy heads at work, I might try a ghetto distillation just for fun!

 

[TasChris]

I agree that the refractometer can be effected heavily by suspended material.
I now take a sample after chilling so that most of the suspended material has dropped to the bottom of the kettle or take a larger sample and crash chill and then test after removing cold break etc.

Cheers
Chris

 

[micblair]

Yeah you could approximate your OG by using the formula below (provided your hydrometer isn't smashed so you can measure your final gravity). Let's say you used US05 and you hit the manufacturers top end attenuation (~80%), with a measured final gravity of 1.010 (because your awesome and you oxygenate your wort, use yiest nutrients and mash at a sensible temperature to maximise fermentability because you enjoy nice sessionable beers).

[(OG-FG)/(OG-1)] x 100 = 80%

[(OG-1.010)/(OG-1)] x 100 = 80%

Rearrange the equations for a while and you get:

OG = 1.050.

If perhaps you were to use a more sensible apparent attenuation value of 75%, your OG would be more like 1.040, which is now a significant amount of error in your calcs, and not a particularly reliable method for approximation.


Anyway, you can play around with some calculated OG's using Wolfram Alpha and replacing OG for X or whatever variable you like, and dialling up/down the apparent attenuation.

 

[jotaigna]

Could it be your mash temp measurement drifting that causes less attenuating wort? Or yeast reculturing to generation 100 has adapted yeasties towards laziness? Both have affected my FG

 

[Bizier]

5 Ways to determine Alc%

1. Density and Refractive Index method
2. Distillation followed by hydrometry/refractometry method
3. Ebulliometer method
4. Gas chromatography (GC) method
5. Spectroscopy (infra red) method

http://www.winegrowers.info/wine_making/Alcohol.

You've tried method 1. I'm guessing methods 3, 4 & 5 are probably out of your league. Leaving Method 2 left to try.

There is also ultrasonic vibration.
I know that it is not particularly helpful to the situation at hand.

 

[Fat Bastard]

micblair: cheers, that looks like an interesting route to go down. Last time I did the IIPA, I got an apparent attenuation of well over 80%.

Could it be your mash temp measurement drifting that causes less attenuating wort? Or yeast reculturing to generation 100 has adapted yeasties towards laziness? Both have affected my FG

I actually suspected yeast, although its only 4 generations old, so I used 2 vials in a 1 litre starter, which went off like a rocket. Temperatures are known to be good. I cross check my HERMS outlet with a callbrates thermometer and its pretty much bang on.

Cheers all!

FB

 

[sponge]

Might be a bit of a dumb question, but have you confirmed correct readings of water with your refrac?

I noticed a few months back I was getting abnormally high readings with my refrac and noticed I was about 10 points out when I measured some tap water.

I've learnt to re-calibrate each brew day with some water at the start of the day to make sure I am reading accurate measurements.