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Approximately how low can the finishing gravity of a beer be? I've been brewing from kits for about 10 years, and went all-grain last year. I wouldn't expect to see anything lower than 1.006 or so, but my latest blew me away -- it was somewhere around 1.000! I couldn't believe my eyes.

Has anyone else seen an FG so low?

(BTW, the yeast was Wyeast 1762, and the SG was 1.066, and table sugar contributed probably only about 1.010-1.015 or so. The grain was all pilsner, and I mashed at about 65 C.)

  • I just had the exact same thing happen with a Belgian Wit using Wyeast 3944, OG 1.046, FG 1.000 (as best I could read it). I was told by my LHBS owner that only bacteria could bring it down to 1.0, but it shows zero signs of infection, one of my best brews. Also, did you mean you wouldn't expect to see anything lower than 1.006? – Mlusby Apr 1 '11 at 13:54
  • Cool, thanks. I don't think there's any significant bacteria in mine, either. And thanks for the correction... I've edited the question. – Jeff Roe Apr 1 '11 at 14:05
  • I just reviewed my recipe and notes and realized my mash was lower than normal ~148F, so that's certainly in line with what Chris mentioned. – Mlusby Apr 1 '11 at 16:40
  • I've gotten below 1.004 a couple times. It seems to always happen when I add external sugar sources (eg. honey). The table sugar could be a factor. – mreff555 Jan 21 at 13:17
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Theoretically, a beer could finish below 1.000 due to the alcohol in it. You'd need to have a very fermentable wort and a very attenuative yeast (or bacteria), but in theory it's possible.

  • 2
    Agreed. Starting at 1.066, 100% attenuation would end you at .984. That would, of course, imply infection. – Brandon Apr 1 '11 at 17:59
  • Brettanomyces yeast are also capable of consuming the more complex sugars that Saccaromyces can't. Also the FG is consistently in the 0.995 range for the wines I make. – Mattress Apr 4 '11 at 16:31
  • There seems to be trend toward adding enzymes to "finish" the conversion of otherwise indigestible sugars to di- and -monosaccharides which the yeast can then process to more ethanol. – 42- Nov 29 '18 at 19:45
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I had a saison that finished at 1.002 that was fermented with Wyeast 3711 French Saison at about 84F. The attenuation rate of the yeast strain along with the use of fully fermentable sugars can bring your final gravity quite low. Your mash temperature will also dictate how fermentable your wort will be, a lower beta amalyes rest will produce more simple sugars.

Lacotbacillus and brettanomyces bacteria will also consume more complex sugars than regular yeast strains dropping the FG below normal levels.

  • My brews with 3711 routinely finish at 0.5 plato (approx 1.002), regardless of OG. 3711, as well as some others, has been identified as var. diastaticus, which means that the yeast create an enzyme with disastatic power, continuing to convert previously unfermentable extract into fermentable extract. Coupled with high alcohol tolerance, this means you can dry your beers right out. – Frazbro Nov 29 '18 at 5:19
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I also just a Belgian Dubbel fermented with 1762 and aged on mission figs to drop to 0.993, down from 1.016 after primary. Doesn't taste infected but drinking early just in case. It is quite alcoholic

  • Since the attenuation has already happened, there's probably no hurry to drink it. In fact, I had an unintensional brett contamination once that was horrible 'cherry pie' flavor. I left it for a month in the garage (up to 80F), then figure I'd get rid of it at the drunken end of a party. But it 'cleaned itself' and actually tasted good! I took it home with me! – Dale Jul 29 '13 at 0:54
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It's feasible to have a "negative" gravity reading; alcohol is less dense than water and if all of the fermentables are gone there's nothing to push the density higher.

I am currently fermenting a Brut IPA, made from all barley and wheat (no adjuncts whatsoever). I used WLP001 and glucoamylase enzymes, and the current gravity reading according to both my refractometer and my Tilt hydrometer is 0.998, or -0.45 °P. I mashed at the low end for sure, never going above 148 and most of the conversion probably happened around 145. I have no reason to suspect an infection (and it's not my first negative gravity beer).

According to the math for adjusting a refractometer reading in the presence of alcohol, you could in practice see an FG as low as 0.990, assuming a very dry, very strong beer (10% ABV) with OG of 1.068. But that's extreme brewing.

  • This is a good answer. However, I'll point out that circumstances have changed somewhat in the 8 years since the original question above was asked in year 2011. At that time, while supplemental enzymes were known (typically Beano was advocated in those days), the Brut IPA style which advocates for use of glucoamylase was not so well known until now. Yeast by themselves, with no additional enzymes or very large quantities of simple sugars, seem to hit a limiting FG of about 1.001-1.002 in "normal" beers. I'm thinking specifically of Belle Saison / Wyeast 3711, which is a great attenuator. – dmtaylor Jun 5 at 22:17
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If you add enough simple sugars, you can probably get it below 1.000.

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I manage to get FG on a Wyeast Labs 3724 French Saison down to 1000. Taste was great too, no infection. In the same batch we also fermented WLP565 Beligian Saison and ended up on 1004. Same base wort, time and temprature as 3724.

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What yeast were you using? Some, such as the 3711 mentioned earlier, are notorious for fermenting out very dry. Many of these are identified as var, diastaticus. These strains can convert longer chain sugars into shorter, more fermentable ones, which leaves very little in the wort that the yeast can't eat. My batches with 3711, regardless of OG, always end up around .5 degrees plato, which is about 1.002.

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Also check malt type. My Pils frequently heads for very low f.g's in the 1000 - 1002 range. Have to be careful if you want to try to keep the abv below 5% (which I do, generally). If anything, the malt ferments too cleanly (I will be heading up the temp range for future mashes).

Edit / update - this stuff was on S-04 (not S-05) apologies. 55% Pale Ale, 35% Pils, 10% others (caramel malts), finished on 1.004 on this same yeast.

  • I checked the yeast and this was safale us-05. – Patrick Walsh Dec 14 '18 at 12:00
  • Finished at 1002, based on the previous batches will be clean but otherwise boring. A summer beer in winter. Next batch (already on), is half minch ale malt, half pils, zeus, cascades and saaz (last), and mashed just under 70C all the way. I am *expecting higher fg on the same yeast. (Started bang on 1050) – Patrick Walsh Dec 14 '18 at 12:03

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