HELP! High FG Reading After Dry Hopping

[brewgasm135]

Short Story:
5 gallon extract w/ specialty steeping grains (Double IPA)
2 weeks in fermenter, SG 1.018 with HYDROMETER
2 weeks later, transferred to secondary and dry-hopped with 3oz of pellets
1 day later, SG 1.045 with REFRACTOMETER
Checked calibration of hydrometer and refractometer, both reading 1.000 with filtered water.



Long Story:
Hey guys. It's been a couple years since I've brewed a batch and I got a free double IPA kit when rebuying some equipment. Anyways, I'm super confused about my gravity readings and need some input.


I brewed an extract kit with specialty steeping grains 4 weeks ago. After finishing up, in a hurry and not caring too much about the results of this first and free batch of beer, I put it away to ferment without taking an OG reading.

Fast forward 2 weeks. Using a hydrometer, I got a reading of 1.018 which I was satisfied with. I waited another 2 weeks, transferred to secondary, and dry hopped with 3 oz of additional hops. A day later, out of curiosity (and having my refractometer come in the mail, I took another measurement with my shiny new tool (which I've used years ago, so I understand how the tool works). SG read 1.045?!?!

So what is going on here?? Beer can't become sweeter or more dense after it has already fermented out, can it? Is it possible the dry hopping is effecting m readings? The refractometer is calibrated, and I just checked the hydrometer and it reads 1.00 with filtered water as well...

The beer tastes like beer, but I'm starting to second guess myself and am tasting a little bit of sweetness, which may just be the maltiness of this recipe. When transferring to secondary yesterday, the batch smelled like a finished beer, and tasted like so, but a bit green, as expected. Today, after taking this way high gravity reading, I cracked the lid off again and took a whiff and it smells a bit hot (alcohol'ish) and kind of sweet.

 

[BlueHouseBrew]

The discrepancy is due to the use of a refractometer. To calculate final gravity with a refractometer you need to know the original brix and the final brix and apply a formula (or use an online calculator). The final gravity will be lower than a straight brix-to-gravity conversion due to the presence of alcohol.

Was your original gravity close to 1.080? If so, the brix reading you have now (roughly 11.2, right?) is essentially equivalent to a final gravity of 1.018.

 

[brewgasm135]

Thanks for the input. My refractometer reads in both Brix and SG. I didn't do any conversions, but just read my FG using the SG side of the refractometer reading. Both refractomer and hydrometer are showing 1.000 with filtered water, as expected. I'm not sure why there is a discrepancy. Unfortunately, I didn't do a OG reading, because I was in a rush and decided to just wing it.

 

[sj3324]

Thanks for the input. My refractometer reads in both Brix and SG. I didn't do any conversions, but just read my FG using the SG side of the refractometer reading. Both refractomer and hydrometer are showing 1.000 with filtered water, as expected. I'm not sure why there is a discrepancy. Unfortunately, I didn't do a OG reading, because I was in a rush and decided to just wing it.

The presence of alcohol throws off the reading of the refractometer.

 

[sj3324]

Did you check your F.G. with the hydrometer after the dry hop?

 

[brewgasm135]

The discrepancy is due to the use of a refractometer. Was your original gravity close to 1.080? If so, the brix reading you have now (roughly 11.2, right?) is essentially equivalent to a final gravity of 1.018.

So I just read the SG reading of the refractometer, but yes, 11.2 is about right on the money with the BRIX side of the reading.

Are you saying... If I take a measurement with a hydrometer and read the SG reading on it as 1.018, then take a refractometer reading of SG (not BRIX), it'll show different? Can you explain this better? Maybe I'm not understanding, but both measurement tools have SG readings on them, so shouldn't they provide the same result?

Thanks again for the input.

 

[brewgasm135]

Did you check your F.G. with the hydrometer after the dry hop?

I was reluctant to "waste" that much of the final beer to take a FG with the hydrometer to compare, but I guess that would be the most definitive answer.

You mentioned that the reading would be skewed in the refractometer, due to alcohol being present. Could you elaborate? I thought the whole point of using it was to get an accurate reading? I guess I'm just not understanding the difference between taking a FG reading with a hydrometer and then expecting the same result with the refractometer.

I'm seeing now that the best to have done, would be to do the OG and FG reading with the same tool, just not understanding the science behind it at the moment.

 

[brewshki]

A hydrometer will read accurately in a solution that contains alcohol. A refract will not. I do not know the exact science, but I believe there is a conversion that can be done to bring it to the correct level. The refract can and will give you an accurate reading before fermentation begins, but not after. It just can't.

 

[botigol]

Maybe I'm not understanding, but both measurement tools have SG readings on them, so shouldn't they provide the same result?

They don't:

"The downsides to refractomers are that they’re more expensive, they require direct light to take a reading, and alcohol will skew the reading. The last of these is the biggest concern. Readings taken after fermentation has started will tend to read higher than they actually are, and some sort of calculator must be used to make a conversion."

http://www.northernbrewer.com/connect/2011/08/using-a-refractometer/

 

[BlueHouseBrew]

Yes, it will show different. Although the refractometer has a SG scale on it, the only thing it measures is the way the light is refracted as it passes through the sample. (It doesn't actually measure density (as a hydrometer does), despite the presence of the SG scale.)

The refractometer is calibrated to measure the effect dissolved sugars have on the refractive index of water. More sugar = higher refractive index = higher brix on the scale. The presence of alcohol in post-fermentation solution increases its refractive index. This makes the refractometer read "high." This is why, although your beer has very little residual sugar, its telling you the brix is 11.2 (1.045 SG).

You can use this calculator to perform the calculation you need in order to determine FG with a refractometer: http://www.northernbrewer.com/learn/resources/refractometer-calculator/

 

[brewshki]

^

 

[brewgasm135]

Thank you so much everyone! Looks like I've got a bit of reading and refreshing to do Love the quick responses from the community.

 

[ba-brewer]

this is a good calculator, also some more stuff to read.

http://seanterrill.com/2012/01/06/refractometer-calculator/

 

[GuldTuborg]

A hydrometer measures liquid density. A refractometer measures the refractive index whatever's in it. Because you're not measuring the same thing, the two instruments will diverge in their readings, regardless of what metric you put on them (SG or otherwise), in certain situations. The presence of absence of alcohol is the one we usually need to worry about.

Anyway, since you asked, that is the why.