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I started brewing about a year ago, currently on my sixth batch, all using extract and some additional grains. My problem is that my beers consistently finish with a higher than expected final gravity. For the life of me, I can't figure out what I'm doing wrong.

My latest batch is the biggest failure yet. I don't think I can bottle it like it is. I modified the all-grain recipe linked below to use extract for the base malt. I did a "mini-mash" with the other grains (crystal, chocolate, smoked, black patent). The temperature at the end of the mash was 150F. I substituted 6 lbs. pale LME and 10 oz. pale DME for the base malt. I upped the second hop addition to a full 1 oz.

http://www.homebrewtalk.com/f126/bert-grants-perfect-porter-tribute-149888/

I plugged this recipe into Brew Target. It said my OG should be ~1.046 and my FG should be ~1.013. My OG was right on target when I pitched the yeast. I pitched one packet of hydrated Nottingham yeast at 74F. The airlock started bubbling within a few hours, went strong for about a day, and then just stopped. After 10 days, the gravity was 1.022. The taste is rather bland, not particularly sweet or bitter or ... anything else, really.

I used tap water from the filtered dispenser on my refrigerator. I aerated by shaking vigorously in the fermenter for a few minutes before pitching the yeast. Fermentation temperature is a consistent 68F.

I asked the proprietor at my LHBS for help. He gave me some yeast energizer and high attenuating ale yeast to try to get it going again. I gently stirred in the energizer and sprinkled the yeast on top. That was about 18 hours ago, and it shows zero activity right now.

Other examples:
Imperial IPA, OG 1.094, expected FG 1.023, actual FG 1.028
Pale Ale, OG 1.052, expected FG 1.013, actual FG 1.018

These things start out with the right OG, but they just stop fermenting and refuse to go any further.

Does anyone have any idea what might be wrong? What I might be doing to encounter this repeatedly? What I can do to salvage my latest batch?

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It's unlikely that simply adding more yeast and supplements (in your case, energizer) will re-initiate the fermentation, you'd need to pitch a starter at high krausen to get it going again. –  Scott Dec 19 '13 at 16:58
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I just wanted to follow up for anyone who might stumble upon this question. I did my first all-grain batch a couple of weeks ago. It went into the fermenter with a gravity of 1.066, and two weeks later the hydrometer read 1.012. I'm completely convinced now that the LME was the reason my final gravity was always high. –  bughunter Jan 27 at 15:24

4 Answers 4

up vote 4 down vote accepted

Well, it's either the yeast or the wort that's giving you the trouble. You can find out by doing a forced fermentation test - take a small amount of wort, and pitch a relatively large amount of yeast (e.g. 1/2 sachet of dry yeast.) Keep it at 75F or more so that the yeast ferment out any fermentable sugars.

After at least 1 day, or once the yeast have sedimented, take a gravity reading. If the reading is the same as your FG (1.018) then you know it's the wort that is the problem. If the FG is lower, then you know it's the yeast that is the problem.

Given the amount of LME, I'd guess it's the wort that is the problem and that you have a lot of unfermentables. Malt extract fermentability can be quite low, so as Denny rightly suggests, you should not subs grain for 100% extract, but use 20% fermentable sugar/80% LME to raise the combined fermentability of LME+sugar.

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I think you're right; it's the LME. As an experiment, I boiled some more DME and added it to the fermenter. It fermented for a day or two, and a few days later the gravity was unchanged from before. The fact that the yeast are clearly capable of fermenting more sugars indicates to me that the wort is just not very fermentable. The LME comprised the majority of the fermentables so that's the likely culprit. Thanks to you all for the input! –  bughunter Jan 2 at 4:08

Fermentation is quick at first, then slows down. 10 days is rarely enough time for a fermentation to complete and if you bottled at that point would have a high probability of exploding bottles. If your gravity is higher than anticipated, LET IT FERMENT LONGER. While initial fermentation will typically happen quickly, you may have to wait 3 weeks or more to reach your anticipated final gravity. In any case, your fermentation is not complete until you have had 3 (or more) successive gravity readings that have not changed. If your readings have not changed, yet your gravity is significantly higher than anticipated, wait another week or 2 just to be safe. Fermenting temperature will also impact the time and attenuation.

Brewtarget is great software and does an excellent job of anticipating final gravity, with that caveat that you have to understand final gravity is a function of the fermentability of your ingredients and the attenuation of your yeast; both of which are variable. However, it should give you a good idea of where you should end. If you have waited long enough for fermentation to complete and you are still significantly higher on your final gravity, check the ingredients you are using and see if you can find better specifications for them and update your ingredients in BrewTarget.

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A few thoughts, and I hope I can answer your question in the process:

  • The only fermentables to speak of will be your malt extracts — the other grain is just adjuncts and will not contribute a significant amount of long-chain sugars for fermentation. So you can pretty much rule out the mash. But as to your malt extract, is it fresh? Do you have any reason to suspect it may be old or have been sitting on the shelf for a long time? Age will affect flavor.

  • Are you oxygenating your wort? Your beers may be petering out due to insufficient oxygen and the yeast is unable to reach optimal attenuation.

  • Are you using yeast nutrients? If not, consider adding yeast nutrient in the last 15 minutes of the boil to help contribute to the development of a healthy cell wall in your yeast cells. This will also help for a complete fermentation.

  • Also, check with the yeast manufacturer for it's potential attenuation range — often you'll have yeast that have a potential attenuation range of 70-75% for example. Use the formula attenuation = (OG - FG) / OG to gauge your apparent attenuation and compare that to what the yeast manufacturer's stated range is.

  • Also look into your yeast handling. If you're consistently having issues with under-attenuation, maybe consider adding yeast starters into the equation and see if that helps with your attenuation issues. An be sure to use a yeast pitching calculator to estimate how much yeast you may need for your recipe/batch. Every recipe is different and may require more or less yeast to start with.

Hope this helps! See this article on BYO.com for some more information on attenuation issues.

Edited: added link and reference to yeast pitching rate calculator.

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Also worth adding is yeast pitching rates. The higher the OG, the more yeast you would need to pitch (bearing in mind dry yeast contains more cells per pack than liquid yeast). I'd put my money on lacking aeration of the wort pre-fermentation and yeast pitching rates. Often times the two biggest culprits. –  Scott Dec 19 '13 at 17:01
    
Correct. There are a lot of good yeast pitching calculators out there that will help one through that process. And yeah, my money's on aeration and pitching rate as well. –  michael t Dec 19 '13 at 17:02
    
I used the Mr. Malty pitching rate calculator on this batch to make sure I was pitching enough. It indicate one packet would be sufficient. I'm sure the yeast was in good shape based on the production date. Unless I somehow damaged it when I hydrated it (in preboiled water at 90F) I think the yeast was OK. –  bughunter Dec 19 '13 at 17:10
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This is not a yeast problem. It is a wort problem. 90F is fine for rehydrating dry yeast. You used plenty of yeast. Your FG is about what I'd predict based on your recipe. –  Denny Conn Dec 19 '13 at 17:21
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Not given the recipe he posted. Besides, the "expected" FG is nothing more than a WAG based on incomplete information. –  Denny Conn Dec 19 '13 at 18:15

First of all, don't trust ANY software to accurately predict FG. All it's doing is making a guess based on the attenuation rating of the yeast. That number is meant for comparing one strain to another using a standardized wort, not as a way of predicting the attenuation you might get. The composition and fermentbaility of the wort is the main determining factor in attenuation. Extracts almost always contain a certain amount amount of unfermentable sugars. Unless you know for a fact that the extract is base malt only, there will likely be at least crystal malt in there. Darker extracts have even more unfermentables. When you then add crystal, chocolate, etc. you're adding even more unfermentables. When I've designed extract kits of my recipes for places like Northern Brewer, I always swap out part of the extract for some sugar. Table sugar, corn sugar, it doesn't matter. By doing that I was able to get an FG very close to the all grain versions and the flavor and mouthfeel were remarkably similar.

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