I have brewed 3 all-grain batches now that have a high final gravity:

Imperial IPA: Target OG - 1.079, Target FG - 1.011, Actual OG - 1.070, Actual FG - 1.020, Yeast - US-05. Common attenuation range seems to be 73% - 78%. Apparent Attenuation: 70%

American Pale Wheat Ale: Target OG - 1.064, Target FG - 1.018, Actual OG - 1.054, Actual FG - 1.022, Yeast - White Labs WLP051. Advertised attenuation range: 75% - 80% Apparent Attenuation: 58%

Belgian IPA: Target OG - 1.060, Target FG - 1.014, Actual OG - 1.061, Actual FG - 1.027, Yeast - White Labs WLP500. Advertised attenuation range: 70% - 75% . Apparent Attenuation: 54%

I brew with Chicago water which has a high ph (around 8), have done 60 minute mashes at about 152 degrees. Originally I was having trouble hitting my OG, but I figured it out and pretty much nailed it on my third brew. But now after fermenting the third beer for 6 weeks, the FG has been stagnant for the latter 2 weeks at 1.027. I just bottled it and am certainly looking forward to trying it, but the FG was way off (13 points, where the first was 9 and the second was only 4). Every time, I aerated my wort and used a yeast starter. Thus I really doubt yeast health is an issue but of course I could be wrong. The Belgian IPA stopped at week 3 at about 1.030, so I added about 6 oz of corn sugar to try and get it going again. The yeast attacked it once I dropped it in, but the FG didn't come down much further. The temperature for each of these was around 65 degrees +- 3. I brought my Belgian IPA into a warmer room so it could stay at a steady 68 after the third week (also when I added more sugar) and it still didn't come down. I have been doing the mash in my 15 gallon brew kettle. I suspect my wort isn't as fermentable as maybe it should be. But I don't know what I'm doing wrong.

My question(s) is this: Before moving forward with another brew, are there any recommendations anybody has to ensure I can get closer to my FG? Would a high ph affect FG in this way? Should I be using a cooler for the mash instead of my stainless kettle? Should I increase the mash time? I have heard the that optimal ph for mash is 5.2 and that the mash process will reach this ph eventually. Should I start the 60 minutes AFTER I reach a ph of 5.2?


There was never a problem with attenuation or FG being off. If anything, my FG readings were below the target. I didn't realize there was a wort correction factor when using refractometers for FG readings.

  • How much crystal malt in the recipes?
    – jsled
    Commented Apr 29, 2014 at 18:38
  • IIPA: 6% crystal and 6% victory. APWA: 7% Caravienne. Belgian IPA: 8% Melanoidin and 8% Caravienne. Commented Apr 29, 2014 at 21:05
  • 1
    No brewing software can accurately predict FG. Don't even bother using it as a target.
    – Denny Conn
    Commented Apr 30, 2014 at 16:58
  • 1
    The attenuation rating of the yeast should only be used to compare one yeast to another using a standardized wort. it is not intended to be the attenuation you'll necessarily get. That's determined by the fermentability of the wort.
    – Denny Conn
    Commented Apr 30, 2014 at 22:33
  • 2
    Just a hint, but imho too many homebrewers brew by numbers, rather than brew by taste. Of course numbers are good for your long term process, but don't think the beer is bad just because the numbers don't show what you are expecting - find a fault first in the taste (e.g. too sweet/dry), and then look to the numbers for help troubleshooting that.
    – mdma
    Commented Jul 9, 2014 at 18:21

6 Answers 6


I'd suspect either a faulty thermometer that's reading deceptively low is to blame, or perhaps your mash water chemistry is really off and you aren't getting full conversion.

For the former, check your thermometer in crushed ice-water to ensure that its reading 32F, and in boiling water to ensure its 212F. Don't be shocked if you can't get it to read 212F in boiling water, being off by a few degrees is fine. Also, if you've got another thermometer lying around, use both simultaneously in the mash and see if there's a difference in the readings.

Optimal mash pH is supposedly 5.2 (at mash temps), and I do believe that if you deviate from that drastically, you can impact your conversion, along with your efficiency. I'd suggest using all Reverse Osmosis water and following a basic water treatment plan, like Gordon Strong's, which simplifies the science a considerable bit.

Finally, make sure you're aerating enough. I've had a couple of high-FG brews lately and I think its a sign that I need to invest in an oxygen setup, but that might be overkill.

  • Good thought on the thermometer. I forgot to mention, after the first brew I was using 2 different ones to make sure I was hitting the correct temps. Commented Apr 29, 2014 at 19:12
  • I would recommend purchasing an alcohol thermometer that you can use to calibrate your other thermometers (they only cost about $10). I have dial thermometers in my brew kettle and mash tun. The first thing I do every brew day is calibrate them so they match the alcohol thermometer at 160F. By doing this, I'm always confident that they are measuring correctly in the mash range where temperature is most important. The dial thermometers are almost always off by a few degrees before calibration.
    – RobM
    Commented Apr 29, 2014 at 22:38

I would focus on the yeast. How old were the yeast packs? Viability and cell count starts to drop off after just a few weeks. How big was the starter and what was the O.G.? Did you use a stir plate? There is a yeast calculator at Mr. Malty that I have found to be helpful. A stir plate helps quite a bit too. Make sure the temperature of your starter is near to the temperature you are planning to ferment at.

  • Yeast was used within 10 days of purchase. Starters were about 1.5 - 2 liters and 1.30 - 1.040 OG. Yes I used a stir plate. I also gave the starter an ice bath until the temp came down under 75. Commented Apr 30, 2014 at 17:51
  • Did you notice the date on the package? They might have been sitting in the shop for weeks or months.
    – jalynn2
    Commented Apr 30, 2014 at 17:53
  • No I didn't. I'll make sure I note that in the future. Commented Apr 30, 2014 at 17:54

Water may be the problem, but I'd focus on some easier solutions first. Confirming mash temp with a second thermometer. Mashing a little thinner (1.5-1.75qt/lb)and cooler (145-149F). And I would strongly recommend repeating one of the same beers you've already made so you can compare the end result with a prior result. THIS IS VITAL otherwise you really compound the ability to figure out what the problem is.

If you want to go down the water chemistry route I'd buy some cheap pH strips initially. Test the water pH and the mash pH and see where you are at. If you are in the 5.0-5.4 ballpark then your FG issues are more likely related to recipe or fermentation.

Lastly, at the end of your next test batch grab a quart of wort an do a forced fermentation test. Put that sterile quart of wort in a two quart sanitized jar. Add half a pack of US05 dry yeast (rehydrated) and let it ferment in warm place (80F). Shake it periodically to make sure they yeast don't settle out to soon. After a week check its SG, if the FG is where you wanted it to be, then you have a fermentation/yeast management issue with your beer.

Good luck


It all comes down to mash temp. Lower mash temps(145-148) will yield more fermentable sugars. Down side is you lower your mash efficiency and need to compensate with more grain or adjuncts. But you will have a substantially dry beer. Even with a iipa you should be able to hit 1.01.


If your pH is that high in your water you'll want to lower it. pH that high will stop conversion/make it take longer. Look at using salts to add base to the water, also make sur eyou are using campden tablets to remove the chlorine and chloramine from your tap water if that what you brew with, yeast hate it.

  • The question is about attenuation. Does pH affect attenuation? I understand that it can lead to poor mash conversion, but surely that would only affect the starting gravity. Commented Aug 6, 2014 at 19:48
  • pH does affect attenuation ^^ Refer to the link for info on pH and attenuation ;) braukaiser.com/wiki/…
    – user8285
    Commented Oct 6, 2014 at 16:13

I'd agree with some of the above answers:

  • Try a new thermometer
  • Try lowering your mash temperatures

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.