Confused, refractometer/hydrometer discrepency

[Troncone]

Making an all-grain Double IPA, OG of 1.071, and I didn't realize that between brewing and the end of fermentation, my hydrometer developed a hairline crack in the bubble end, allowing enough liquid to get in to make my FG appear lower.

After it completely broke (like the 10th I've gone through) I bought a refractometer. When it arrived, I retested the batch (after I had already cold-crashed it thinking it was 1.010) and it showed a post-fermentation gravity of 1.034, a Brix of about 8.5, give or take.

When I plug that into any of the online converters for post-fermentation refractometer readings, they convert a 17 Brix OG (1.071) and an 8.5 Brix FG to 1.012, which is recipe spot-on.

BUT I bought a new hydrometer and tested the batch last night, and the hydrometer says 1.026.

I don't understand how these two things can peacefully coexist and I'm really looking for some guidance from those more experienced than I. I have to be doing something wrong because I have four batches going right now and none of the conversions seem to jive with the hydrometer readings.

Thanks in advance and cheers.

Single infusion, 152 degrees, mash out to 170

10 lbs Pale Malt (2 Row)
2 lbs 8.0 oz Vienna Malt
1 lbs Oats, Flaked
12.0 oz Cara-Pils
8.0 oz Caramunich
1 lbs Corn Sugar

1.00 oz Columbus (Tomahawk) [14.00 %] - Boil 60
1.00 oz Citra [14.00 %] - Boil 20.0 min
3.00 oz Citra [14.00 %] - Boil 5.0 min
3.00 oz Citra [14.00 %] - Steep/Whirlpool 30.0min California Ale (White Labs #WLP001)
3.00 oz Citra [14.00 %] - Dry Hop 7.0 Days

 

[BoomerHarley]

Best thing you can do is to test them both on DI water to see how well they are calibrated. They may also not be temperature compensated.

 

[Garou24]

I do not use refractometers, but I thought you could not use them once you added yeast. The alcohol the yeast produces causes the results to not read true.

 

[BrewCrewKevin]

hm.... interesting.

I agree with Boomer. Try them both just with water. Do they both show right around 1.000?

Normally I would say trust the Hydrometer post-ferment, because even with converters, refractometers are just not made for it. However, it actually sounds like the refractometer makes more sense....

 

[Hello]

I've avoided arguments with folks who really claim that a refractometer can be used once the wort ferments. I understand fully that there are calculators out there, but for me I've found that my tests result in the refractometer being off and the hydrometer being where I thought the FG should be.

I also noticed that after leaving a beer in the carboy for 2 months, the FG read 1.014 and the refractometer read higher. I just can't trust anything but the hydrometer for some reason.

Your situation is different, which is odd. I would do the water test and also, is the refractometer adjusting automatically for temperature?

 

[user 171019]

Did you try Vinocalc, which does some nifty calculations to compensate for alcohol in refractometer reading.

Sent from my C5155 using Home Brew mobile app

 

[ajdelange]

A hydrometer measures the density of anything it is immersed in. Marked with scale that displays the w/w concentration of sucrose solutions (the Plato or Brix scales) a hydrometer can be used to indicate the amount of sucrose in a solution. Of course our solutions (wort) are not pure sucrose. In fact that contain rather little. But as it turns out solutions of brewing sugars all have densities that are very similar to those of solutions of sucrose and so the sucrose calibration is a pretty good indicator of 'extract', the sum of all the dissolved sugars.

A refractometer measures the ratio of the velocity of light propagating in the test solution to that in a vacuum. Marked with a scale derived from meaurements of sucrose solutions of known strength the RI readings can be used as an indicator of the strength of an unknown sucrose solution. If a solution of a different sugar behaves similarly to sucrose then we can use the sucrose scale to estimate the strength of that solution too. The problem is that with wort not all the sugars behave in the same way as sucrose and, depending on the actual spectrum of sugars in the wort, the Brix reading may be appreciably in error relative to the hydrometer reading. To be off by 1 or more Bx in unfermented wort is not unusual at all. Alcohol shifts RI in the same direction as sucrose causing the Bx reading to be higher than it would be if the solution were pure sucrose. For these reasons refractometers are not used in brewing unless they have been calibrated for the beers being tested against precision hydrometers or electronic density meters.

 

[iaefebs]

In order to go through 10 hydrometers, you must have had a lot of brew sessions. (I still have my original 10 year old one) You got the readings you expected with the refractometor and the hydrometer was unexpectedly high. You know your process was good while making the beer. So I'd say you got a bad hydrometer.
I also recommend to anyone that when you are taking FG readings with your hydrometer take a drop of that from your tube and try your refractometer, using a calculator and decide for yourself if the reading is accurate or not.

 

[bknifefight]

Does it taste like 1.012 or 1.026? Those FGs will taste significantly different.

 

[bobtheUKbrewer2]

if a finished beer is AROUND 5% ABV the hydrometer will ONLY give you the average of the (by now quite dilute ) unfermented wort and the ? % alcohol in water solution - you don't know EITHER figure

 

[Troncone]

Okay, thanks everyone. Still not entirely un-confused, but...

They both go to 1.0000 with water, so that's not an issue. I was hoping the calculators, vinocalc and others, on the refractometer reading would be correct, but that doesn't seem the case. The hydrometer just uses so much damn beer... Definitely not a bad hydro. I bought two because I break so many and tried them both just in case.

The calculators must be off.

So, now, it seems, that thanks to a small crack in the hydrometer I bottled two beers that had not reached their proper FG. I only bottled on Friday, so the question becomes, and forgive me if this is stupid, can I pour the bottles back into a carboy and repitch yeast, or am I screwed at this point?

And, yeah, it definitely tastes sweeter than a .012 should taste.

For the record, here was the calc:

 

[ajdelange]

There is one sugar solution on which a Brix calibrated hydrometer and a Brix calibrated refractometer will agree and that is the one in which the sugar content is 0 (i.e. distilled water). Thus comparing the two with distilled water doesn't tell you anything other than that neither of them is broken (or in need of cal) if they both read 0.

 

[bobtheUKbrewer2]

open 1 bottle after 5 days if it is excessively gassy open all the others and reseal after 10 minutes - topping up if necessary. Repeat in another 5 days.

 

[frankvw]

I had a discussion like this with one of my brewing mates recently. He uses both hydrometers and refractometers, and so far I've never seen the two agree on anything except the gravity of distilled water at 20 degrees Celcius.

However. Said mate is also notorious for taking erroneous gravity readings. He's often come up with hydrometer readings of 1.100 or more when a quick look at the amount of fermentables clearly shows that 1.050 or so is the best thing possible. Or he's measured a FG of 1.010 in a wort that tastes cloyingly sweet.

Therefore I would recommend several readings, taken from samples collected from both the top and the bottom of the fermenter (unless you're not afraid to stir your beer, but I'd still take multiple samples).

In closing, I have been left severely underwhelmed by the quality of equipment imported from China, including refractometers. A good, professional quality lab-grade refractometer is expensive, but in the end it may be cheaper than buying three cheapies in a row which all have to be replaced because they're inaccurate to the point of being worse than useless.

Unfortunately, most LHBS's have fallen for the lure of purchasing their goods dirt cheap from a Chinese importer. :-(

// FvW

 

[Troncone]

Thanks guys. Appreciate the help.

Here's a dumb question, can I unbottle and repitch if there are still fermentable sugars in the beer? Only been in bottles 5 days.

 

[Safa]

Probably no need to repitch. Do what poster above suggested.

 

[bobtheUKbrewer2]

my earlier post says undo and reseal - no need to re-pitch IMHO

 

[Troncone]

Thanks. Just not understanding what that will do to lower the gravity? It's at 1.028 right now.

 

[bobtheUKbrewer2]

as the pressure increases the fermentation rate decreases or practically stops - so releasing the pressure (if there is any) will help - 1.028 is very high and if there is no pressure add more yeast.

 

[Troncone]

Gotcha. Thanks.