Consistently poor attenuation

[rmar5494]

All,

Long time lurker, first post. Been brewing off and on for about 6 years.

I’ve turned in about 6 all grain BIAB batches and each time fermentation craps out at around 1.020 regardless of dry or liquid yeast or ingredients. Two choices seem to be either poor yeast health or unfermentable wert.

Most recent batch hit target OG on the nose and pitched rehydrated US-05. Again, all well until around ~AA and there she stays. With OG ok I’m assuming there’s no trouble with fermentability and fermenting in temp controlled chamber. Any ideas?

Sincerely,

stumped and frustrated

 

[RM-MN]

Mash temperature, pitch rate, recipe, time, and fermentation temperature all play a role in where you final gravity ends up. I start the ferment in the low to mid 60's and after 5 to 7 days let it warm to low 70's. By day 10 it is usually at FG and ready to bottle. What temperature is your fermentation chamber set for? Too cool will put the yeast to sleep before they complete.

 

[ESBrewer]

Hitting the expected OG is not the same thing as producing a fermentable wort. OG is affected by almost everything that is extracted from the grains (=mainly starch and its derivatives) but fermentability depends on the amount of fermentable sugars that are the end products when the huge starch molecules are broken down to very simple sugars that can be utilised by yeast cells. So, hitting the OG means that you have extracted the starch from the grains succesfully, but it does not tell you whether it has been effectively broken down to sugars by mash enzymes (=amylase enzymes from barley). You should recheck your recipe for the amount of base malt (the enzymatically active malt). It should be high enough to provide the aforementioned enzymatic activity. Too high amount of some specialty grains brings nonfermentable sugars to wort and thus raise the final gravity. And ensure that your mash protocol and conditions are correct (especially time and temperature but pH will also play role here).

 

[rmar5494]

66* for 5 days then ramped to 71 when I pulled 1.020 hydrometer sample. I should probably re-examine thermometer calibration too. Is it possible to hit OG while also creating wert with lots of unfermentables if mash temp was erroneously high?

Thanks for your help

 

[ESBrewer]

Is it possible to hit OG while also creating wert with lots of unfermentables if mash temp was erroneously high?

Thanks for your help

Absolutely, this is exactly what high mash temperature does - it increases body (and FG) by destroying the enzymatic activity so early in the mash that not all the starch gets converted to fermentable sugars. For an effective mash aim for something like 150-152F for an hour (or a bit longer) and ensure that your thermometer works as expected.

 

[rmar5494]

Recipe was as follows:

10lbs pale ale
1lb victory
1lb C40
0.15lb blackprinz

I’ve not had trouble with yeast and fermentation conditions in many batches of extract or partial mash. Given the info you provided I’m guessing my mash temps were too high and I’m creating problematic wert.

I pitched in 1.5tsp beta amylase and another yeast pack. If that brings gravity down I suppose it will confirm the wert fermentability issue.

Thanks-should have asked on this forum a long time ago.

 

[bpgreen]

If you add beta amylase, you need to make sure thou take steps to denature it before bottling. Otherwise, it'll continue to chew through unfermentable sugars and make them fermentable.

This can lead to bottle bombs or gushers (my sister's brother has a stain on his ceiling after trying this once).

The easiest way to denature enzymes is heat. If you heat it enough to kill denature the enzymes, you'll also kill the yeast, so if you're naturally carbonating, you'll need to add more yeast.

 

[rmar5494]

How high does the temperature need to be to denature the enzymes?

I’ve unfortunately had to do this before, although without problems as I now keg.

 

[day_trippr]

If the results are that consistent I would suspect whatever thermometer is being used to check the mash temperature...

Cheers!

 

[chrisisnapping]

is it possible your hydrometer is off? i'd test it with some RO or distilled water to ensure accuracy.

How big of batches are you doing?