[tporco]

Brewed my first AG batch a week or so ago, an Irish Stout.  I know that Stouts are not generally stronger beers, but I am concerned that my final alcohol content is low, way low.  I am estimating it at at 2.58%.  OG was 1.042 and FG was 1.018. 

The cause has been rolling around in my head since first measuring the FG.  Started thinking that it might be the efficeiency in the mash tun, but ran the numbers this AM and come up with a 79% efficiency which I don't think is unreasonable at all. 

I am looking for some guidance on where i should be looking - is it more likely my issue is at the mash step or somewere else down the line?  Any suggestions would be appreciated. Thanks.

[jeffy]

Brewed my first AG batch a week or so ago, an Irish Stout.  I know that Stouts are not generally stronger beers, but I am concerned that my final alcohol content is low, way low.  I am estimating it at at 2.58%.  OG was 1.042 and FG was 1.018. 

The cause has been rolling around in my head since first measuring the FG.  Started thinking that it might be the efficeiency in the mash tun, but ran the numbers this AM and come up with a 79% efficiency which I don't think is unreasonable at all. 

I am looking for some guidance on where i should be looking - is it more likely my issue is at the mash step or somewere else down the line?  Any suggestions would be appreciated. Thanks.

I did a quick calculation and found that you have 2.89 ABV right now and that if it had stopped fermenting at say, 1.012 you'd have 3.95 ABV.  Since it has only been a week, you may want to see if attenuates any further.  If it does not, then you may want to change your recipe or your mash temps to make the wort more fermentable, such as lowering the mash temps to the upper 140's or lower 150's.
More info on the recipe would help with diagnosis.
Either way, a dry stout is low in alcohol and will still be packed with flavor.

[bonjour]

Don't confuse efficiency with attenuation.

efficiency is the extraction of sugars from the malt.  79% if fine.

Attenuation is the conversion of the extracted sugars into alcohol.  75% attenuation would put you in the 1.010-1.011 range, obviously your attenuation is currently less than that.

Three easy causes, the fermentation is not finished,  The yeast will finish in it's own time.  check the FG again and esee if it has changed.

the other is mash temp,  If you mashed high that could be the reason. 

The final reason is grain bill.  Too many non-fermentables could be the cause.

The recipe and your process (time and temps, will help us help you

[svejk]

When you tell us about your process, in addition to mash temps, please let us know how much yeast you pitched, whether you made a starter and how you aerated the wort.

[tporco]

Thanks for all of the comments here guys.  Based on your input I am thinking that the most likely scenario is I overshot the step mashing of the grain which hurt me in the long run.  The recipe I was attempting to follow had a 133F hold for 30 min, and then more water and step to 158F for 45 min.  I am thinking I probbaly overshot the 158 by 10-15 degrees before bringing it back into range.  I am using a propane turkey fryer type heater and admittedly it does not have the most precised temperature control. 
To safegauard against this in my next batch I think I am going to drop back to an infusion mash rather than a step. 

Anyway, I think we have a cause, but here is some of the additonal info if you have any additional insight I would love to hear it.
Grain Bill: 6# American 2 row pale malt, 1# English Carmel Malt, 1# Roasted Barley, 1/2# Black malt. Hops: 1/4 oz 1st gold , 1/2 oz kent, 1/2 oz williamette all during the boil - 60 min.
Yeast was a Wyeast 1084 Irish Ale - pitched directly in the wort. 

[denny]

There is really no need at all to do a step mash, especially a protein rest, with that grist.  You're not only making more work for yourself, it could be detrimental to the head and body of the beer.

[svejk]

I think overshooting your saccarification rest by 10-15 degrees is the probable cause as well. Once when I overshot my temp significantly, I told my brother to quickly get some cool water to bring it back down to the right temp. He said, "isn't that like cooking an egg until the yolk is hard and then quickly cooling it down so it'll go back to over easy?". I didn't have an answer.

As long as your Wyeast yeast was a reasonably fresh XL smack pack that was fully plumped up when you pitched it, and the wort was really well aerated, you can get away without a starter in a batch of 1.042 wort.  That said, since so much effort is put into a brew day, making starters is a really good practice to get into.  Put another way, if you ever have a batch in the future where you don't hit your target final gravity, and you pitched a healthy starter and aerated it well, then you can eliminate underpitching as a possible cause.

[euge]

There is really no need at all to do a step mash, especially a protein rest, with that grist.  You're not only making more work for yourself, it could be detrimental to the head and body of the beer.

That is sage advice per my experience.

I get 3.2% ABV per your gravities. That's a typical session beer and can get you fairly buzzed in no time. If you need it "stronger" then you might add some Everclear- don't do it blindly, but do a separate graduated taste test. You'll need some sweetness to counter the added alcohol but 1.018 might work in your favor in this case.

Or leave it as is and enjoy. Looks like it's a decent beer already. A learning experience.

[tporco]

I think overshooting your saccarification rest by 10-15 degrees is the probable cause as well. Once when I overshot my temp significantly, I told my brother to quickly get some cool water to bring it back down to the right temp. He said, "isn't that like cooking an egg until the yolk is hard and then quickly cooling it down so it'll go back to over easy?". I didn't have an answer.

As long as your Wyeast yeast was a reasonably fresh XL smack pack that was fully plumped up when you pitched it, and the wort was really well aerated, you can get away without a starter in a batch of 1.042 wort.  That said, since so much effort is put into a brew day, making starters is a really good practice to get into.  Put another way, if you ever have a batch in the future where you don't hit your target final gravity, and you pitched a healthy starter and aerated it well, then you can eliminate underpitching as a possible cause.

Forgive my ignorance here, but can you elaborate on what constitutes a "starter"?  Brewed my second batch with the Wyeast smack pack.  This time let it plump for 4 hours before pitching, but if I am reading you right, you are referring to something else.

[denny]

Forgive my ignorance here, but can you elaborate on what constitutes a "starter"?  Brewed my second batch with the Wyeast smack pack.  This time let it plump for 4 hours before pitching, but if I am reading you right, you are referring to something else.

You're correct.  Letting a smack pack swell does not constitute a starter.  The purpose of a starter is to increase the number of yeast cells before pitching the yeast. When a smack pack swells, there is virtually no cell growth.  It's just a method of ascertaining the viability of the yeast.  For info on making starters and how big a starter you need, see www.mrmalty.com .

[svejk]

Yep - the Mr Malty "14 Essential Questions About Yeast Starters" says everything way better than I ever could. I also think going to youtube and searching for "yeast starter" is a good idea.  Watch a few of the videos and it will help you visualize the process.

Once you have made the starter, cooled it and pitched the yeast, it needs to be well aerated because the yeast use oxygen to multiply. That means you shake the container vigorously every chance you get.  Some of the videos suggest putting an airlock on the container, but I believe that covering the top with foil has been shown to be superior at growing more yeast.

I hope this helps.   

[tschmidlin]

I think overshooting your saccarification rest by 10-15 degrees is the probable cause as well. Once when I overshot my temp significantly, I told my brother to quickly get some cool water to bring it back down to the right temp. He said, "isn't that like cooking an egg until the yolk is hard and then quickly cooling it down so it'll go back to over easy?". I didn't have an answer.

Next time tell him it's like putting the egg into a scorching hot pan you accidentally pre-heated on high,  and then taking it off the heat before the egg burns.  It's not ideal, but the egg doesn't burn (and the enzymes in the mash don't denature) instantly.

[euge]

Regardless, looking back on it 158F is pretty high by convention. I'm surprised you've hit 1.018 at all. So probably you really weren't that high due to the imbalances in a direct fired mashing process. Convection and mixing etc...

Try batch sparging at a single infusion temp- say 153F...?

[tschmidlin]

Fair enough euge, I mash my Irish stout at 150F.

[Kit B]

Regardless, looking back on it 158F is pretty high by convention. I'm surprised you've hit 1.018 at all. So probably you really weren't that high due to the imbalances in a direct fired mashing process. Convection and mixing etc...

Try batch sparging at a single infusion temp- say 153F...?

Agreed...158* is high.
Shoot for low 150s, if you can't get precise control of your burner.
That will make all the difference in the world.