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General Category => Yeast and Fermentation => Topic started by: jc24 on July 13, 2017, 10:58:15 pm

Title: Attenuation question
Post by: jc24 on July 13, 2017, 10:58:15 pm
Hi all, I am wondering if my low apparent attenuation levels are normal or indicative of a problem in my process.

The following is true for each brew:
- I brew using Briess liquid extract with a partial mash, partial boil (11L boil volume diluted to 21L in the fermenter)
- I aerate using a KegKing Vortex aerator for 2mins
- I make the recommended starter size, using a stir plate
- yeast is usually 2-4 weeks old, stored refrigerated
- my fermentation temperatures are controlled using a fridge and an external temp. controller. I pitch 1 - 2°C below fermentation temp and raise it up a few degrees half way through fermentation
- I add 1/8 tsp yeast nutrient to the starter, and another 1/4 tsp to the boil

Some recent brews:
Oatmeal Stout, Wyeast 1968, I got 64% attenuation (Beersmith estimated 71%, Wyeast advertise 67% - 71%)
Foreign Extra Stout, Wyeast 1028, I got 63% attenuation (73 - 77% advertised)
Wee Heavy, Wyeast 1056, I got 71% attenuation (73 - 77% advertised)
Irish Red Ale, Wyeast 1084, I got 69% attenuation (71 - 75% advertised)
Dusseldorf Altbier, Wyeast 1007, I got 72% attenuation (73 - 77% advertised)

Is this normal? If not, where could I be going wrong? Thanks in advance!
Title: Re: Attenuation question
Post by: flars on July 13, 2017, 11:27:45 pm
Do you use a refractometer or hydrometer for specific gravity?  The refractometer won't be accurate in the presence of alcohol.

Everything you are doing seems right.  Would need some details on the fermentation if the problem is not with using a refractometer.
Title: Re: Attenuation question
Post by: mainebrewer on July 14, 2017, 04:37:25 am
I'm not familiar with Briess extract but some extracts are less fermentable than others.
Also, while attenuation in the mid 60's to low 70's is lower than expected, the manuf and Beersmith estimates are just that, estimates.
Try doing a fast ferment test of your wort. That will tell you exactly how much attenuation you can expect from your wort and yeast combination.
To do the test, after you pitch the yeast, take a small amount (80z or so) of the wort and place it in a covered container. Keep it warm, shake it up whenever you think of it. The sample will ferment out pretty quickly and then you can measure the final gravity. 
Title: Re: Attenuation question
Post by: jc24 on July 14, 2017, 05:13:08 am
Do you use a refractometer or hydrometer for specific gravity?  The refractometer won't be accurate in the presence of alcohol.

Everything you are doing seems right.  Would need some details on the fermentation if the problem is not with using a refractometer.

Measurements are taken using a hydrometer. A common ale fermentation profile for me would be to pitch at 18°C, ferment at 20°C until fermentation was half done (usually 2-3 days), then increase temp to 23°C and leave in primary for an additional 10-12 days. I'll then cold crash to 3°C for around a week and then keg.

As far as the starter goes, I'm still experimenting, but if the starer volume is 1L or less I prefer to pitch the whole thing at high krausen. In this case, I'll ferment the starter at pitching temp. If the starter volume is greater than 1L I'll let it ferment out on the stir plate for 2-3 days at 23°C, leave it in the fridge overnight, decant and pitch. I can only assume I'm getting the right cell counts as I have no way of measuring at the moment.
Title: Re: Attenuation question
Post by: jc24 on July 14, 2017, 05:16:03 am
I'm not familiar with Briess extract but some extracts are less fermentable than others.
Also, while attenuation in the mid 60's to low 70's is lower than expected, the manuf and Beersmith estimates are just that, estimates.
Try doing a fast ferment test of your wort. That will tell you exactly how much attenuation you can expect from your wort and yeast combination.
To do the test, after you pitch the yeast, take a small amount (80z or so) of the wort and place it in a covered container. Keep it warm, shake it up whenever you think of it. The sample will ferment out pretty quickly and then you can measure the final gravity.

Thanks for the reply. Yes I've tried a few different manufacturers for the extract, and they all seemed just as fermentable as each other. And yep I definitely plan to do some a forced ferment and diacetyl test on my next brew - that will at least help me narrow the problem down a little.
Title: Re: Attenuation question
Post by: dmtaylor on July 14, 2017, 06:30:03 am
Yes, this is your problem:

- I brew using Briess liquid extract

Try dry malt extract instead.

I'll just leave this here as well:

(https://farm5.staticflickr.com/4232/35033210393_37d5c0f7a8_b.jpg)
Title: Re: Attenuation question
Post by: Iliff Ave on July 14, 2017, 09:20:44 am
When I was extract brewing I had the same issues with attenuation. I started subbing in some plain old table sugar for a portion of the fermentables which made a huge difference. It looks like that tip is included in dmtalyor's post...
Title: Re: Attenuation question
Post by: mabrungard on July 14, 2017, 11:33:34 am
Many roast malts contribute low fermentability that is in the 40 to 60 percent range. So you can expect to have your dark beers not attenuating quite as well as a pale beer mashed at the same temp and fermented with the same yeast.
Title: Re: Attenuation question
Post by: Joe Sr. on July 14, 2017, 02:55:17 pm
Are you using dark malt extract?  That could be an issue.

When I use extract, I use Breiss Pilsen DME.  It's the lightest and most fermentable extract I have encountered.  To make a stout, I simply use all the dark grains you would normally use to get the color I want.

I've had no issues with attenuation with Breiss Pilsen DME.
Title: Re: Attenuation question
Post by: HoosierBrew on July 14, 2017, 03:32:08 pm
Are you using dark malt extract?  That could be an issue.

When I use extract, I use Breiss Pilsen DME.  It's the lightest and most fermentable extract I have encountered.  To make a stout, I simply use all the dark grains you would normally use to get the color I want.

I've had no issues with attenuation with Breiss Pilsen DME.


Yeah, I use Briess pils DME for hop trials. IIRC it's supposed to be ~ 80% fermentable, a good bit higher than most extracts. But take a dark malt extract - notoriously low fermentability - and add crystals and more dark steeping grains (both present in the dark extract already), and attenuation goes to hell/FG goes up.
Title: Re: Attenuation question
Post by: jc24 on July 14, 2017, 05:22:17 pm
Yes, this is your problem:

- I brew using Briess liquid extract

Try dry malt extract instead.

I'll just leave this here as well:

(https://farm5.staticflickr.com/4232/35033210393_37d5c0f7a8_b.jpg)
Thanks! Why is DME more fermentable?
Title: Re: Attenuation question
Post by: jc24 on July 14, 2017, 05:23:51 pm
When I was extract brewing I had the same issues with attenuation. I started subbing in some plain old table sugar for a portion of the fermentables which made a huge difference. It looks like that tip is included in dmtalyor's post...
I've actually been using dextrose to try and help which is why I'm still confused!
Title: Re: Attenuation question
Post by: jc24 on July 14, 2017, 05:25:51 pm
Many roast malts contribute low fermentability that is in the 40 to 60 percent range. So you can expect to have your dark beers not attenuating quite as well as a pale beer mashed at the same temp and fermented with the same yeast.
True, but I'm experiencing low attenuation on beers with no specialty malts at all...
Title: Re: Attenuation question
Post by: jc24 on July 14, 2017, 05:27:43 pm
Are you using dark malt extract?  That could be an issue.

When I use extract, I use Breiss Pilsen DME.  It's the lightest and most fermentable extract I have encountered.  To make a stout, I simply use all the dark grains you would normally use to get the color I want.

I've had no issues with attenuation with Breiss Pilsen DME.
Interesting - i usually use their Pale extract which does seem too dark. 8°L if I remember correctly
Title: Re: Attenuation question
Post by: jc24 on July 14, 2017, 07:15:10 pm
Thanks for all the helpful replies, I'll try using DME on my next brew and do a forced ferment test and let you know how it goes.
Title: Re: Attenuation question
Post by: Big Monk on July 14, 2017, 07:24:31 pm
Are you using dark malt extract?  That could be an issue.

When I use extract, I use Breiss Pilsen DME.  It's the lightest and most fermentable extract I have encountered.  To make a stout, I simply use all the dark grains you would normally use to get the color I want.

I've had no issues with attenuation with Breiss Pilsen DME.
Interesting - i usually use their Pale extract which does seem too dark. 8°L if I remember correctly

If you look at the spec sheets for the Briess DME, you'll see that for a fixed volume, the color goes up with gravity. For example, for their Pale Ale and Golden Light extracts, the colornin °L is 3, 4, 5, 6, and 7 for 1.020, 1.030, 1.040, 1.050, and 1.060 respectively.
Title: Re: Attenuation question
Post by: dmtaylor on July 14, 2017, 07:25:12 pm
Yes, this is your problem:

- I brew using Briess liquid extract

Try dry malt extract instead.

Thanks! Why is DME more fermentable?

DME isn’t more fermentable than LME.  It’s just less twangy, i.e., doesn’t stale as easily.

I was also under the (mistaken?) assumption that your darker beers had lower attenuation because in fact darker extracts are less fermentable than lighter ones, as others mentioned as well.
Title: Re: Attenuation question
Post by: jc24 on August 05, 2017, 06:13:29 am
Thanks for the help on this everyone - switching to Briess Extra Light DME seems to have done the trick. Just finished fermenting a Red Ale and it finished up at 1.010 (I did have 7% dextrose). Happy days!
Title: Re: Attenuation question
Post by: bboy9000 on August 05, 2017, 10:49:16 pm
Good tips on sheet posted.  A side note on the item "Why do all my beers taste the same?"  That could be from too many types of specialty malts too. 

For attenuation make sure you are making temperature corrections  when reading the hydrometer.