Thought my fermentation was stuck. Turns out I just don't know how to use a refractometer. Now it seems my FG is SUPER low!

[parkerdel]

Explanation above. Recipe below.

So I brewed a pretty normal pale ale and after day 6, when all signs of fermentation ceased, I took a gravity reading with my refractometer to see where it was at. The reading was 1.025 SG. Wow, seems high I said to myself. Maybe I'll give it a few more days and see where were at. Fast forward 4 days later to today when I took another reading. Hmm still at 1.025... Maybe I have a stuck fermentation? So I Google, and I Google. I ask ChatGTP. I ask Grok. Hours upon hours of research. Agonizing pain and suffering. What the hell is going on with my beer!?! (RDWAHAHB right?) Finally, after several hours, I come across a post that says, "are you using a hydrometer or refractometer, because refractometers give inaccurate FG readings due the the presence of alcohol"... MOTHER F####R! So I go find a refractometer conversion calculator online (a few actually) and see where I'm at. Based on those calcs I'm at a FG of 1.005; which is an apparent attenuation of 91% with WLP-001? That doesn't seem right either. Maybe I'm doing my calcs wrong.

My refractometer is an unbranded one I got from my LHBS, model No. RSG-100/ATC. It has both Brix (on the left) and SG (on the right) of the read out. I've calibrated it using distilled water to read at zero. I measured my OG on brew day right before I pitched the yeast (the wort was measured at 70F) at 1.055 SG. And as I said before my current reading today after 10 days of fermentation is 1.025 SG (matching my day 6 reading). Correcting the 1.025 using both the Brewer's Friend and Brewfather refractometer calculator, results in a corrected SG of 1.005.

Does any of this seem right to you?

Oh yea and I don't have a hydrometer. It broke a while back which is why I bought the refractometer!

Anyway thanks for reading this far if you made it here.

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Citra Pale No. 2​

American Pale Ale
All Grain
Batch Volume: 5.5 gal
Boil Time: 60 min
Mash Water: 3.88 gal
Sparge Water: 4.23 gal @ 170 °F
Total Water: 8.11 gal
Boil Volume: 6.99 gal

Vitals​

Original Gravity: 1.055 (measured with refractometer)
Final Gravity: 1.005 (1.025 measured with refractometer corrected to 1.005)
IBU (Tinseth): 33
Color: 5.4 SRM

Mash​

Strike Temp — 165 °F
Temperature — 152 °F — 45 min (152F at min 1, 151F at min 45)

Malts (12 lb)​

10 lb (83.3%) — Root Shoot Malting Genie Pale — Grain — 2.1 °L
1 lb 8 oz (12.5%) — Briess Caramel Malt 10L — Grain — 10 °L
8 oz (4.2%) — Weyermann Carapils/Carafoam — Grain — 2 °L

Hops (3 oz)​

1 oz (30 IBU) — Citra 14.1% — Boil — 45 min
1 oz (3 IBU) — Citra 14.1% — Aroma — 10 min hopstand
1 oz — Citra 14.1% — Dry Hop — day 5

Miscs​

1.44 g — Epsom Salt (MgSO4) — Mash
4.64 g — Gypsum (CaSO4) — Mash
2.4 ml — Lactic Acid 80% — Mash (adjusted to 5.4pH)
1.56 g — Epsom Salt (MgSO4) — Sparge
5.06 g — Gypsum (CaSO4) — Sparge
3.03 ml — Lactic Acid 80% — Sparge (adjusted to 5.4pH)
1 items — Whirlfloc — Boil — 15 min

Yeast​

1 pkg — White Labs WLP001 California Ale 80%
0.7 L starter
2.72 oz DME
228 billion yeast cells (estimate)
Pitched into 70F Wort

Fermentation​

Primary — 68 °F — 10 days
Cold Crash — 38 °F — (*I'm here, in day 1 of cold crash just took a gravity reading prior to lowering the temp)
Carbonation: 2.4 CO2-vol

Water Profile​

Ca2+ 115 | Mg2+18 | Na+ 85 | Cl- 66 | SO42- 300 | HCO3- 135

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[day_trippr]

fwiw, I have a 52 point hazy sitting at 1.006 FG right now using 1388 (not the most attenuative strain) so I would say what you're measuring is within the realm of plausibility...

Cheers!

 

[hungupdown]

I've tried various calculators to give FG from initial and final refractometer readings. And
They never match The (corrected for temp) FG given by by fairly accurate hydrometer. I've not broken (my second one) yet.

The error is worse with higher gravity beers. I suspect it's due the mix of sugars here, containing lower percentages of sucrose. As domestic hydrometers generally are calibrated for just sucrose.
And on these, the Brix Scale calibrates the number of grams of pure cane sugar (sucrose) contained in 100mL of water.

Commercial refractometesr are available, which are calibrated for the refractive index of other common types of sugar. But again, they're only accurate for that one sugar type.

Refractive index, doesn't matter to hydrometers.

 

[parkerdel]

Sounds like the refractometer is only good for OG readings on brew day. Looks like I need to bite the bullet and get a hydrometer, or maybe I can finally use this as an excuse to get a Tilt.

 

[RM-MN]

Looks like I need to bite the bullet and get a hydrometer

Buy two. If you only get one it gets lonely and finally commits suicide just like your first one did. I bought 2 and one has never been used in years.

 

[mac_1103]

A tilt isn't going to give you particularly accurate FG readings either. Great for knowing how your fermentation is going though.

Also, this.

 

[doug293cz]

And on these, the Brix Scale calibrates the number of grams of pure cane sugar (sucrose) contained in 100mL of water.

This is not the correct definition of Brix, or Plato. Both are defined as weight percent of sucrose in a water solution. The formula for weight % is:

Wt % (or °Brix or °Plato) = 100% * wt of sucrose / wt of solution = 100% * wt sucrose / (wt sucrose + wt water)​

​

The more sugar in solution the more the quoted definition differs from the correct definition.

Brew on