Low attenuation/missing FG on all batches

Ingredients
1

Hi Team,

I have been having some issues on the last 5 brews I have done (since getting a new system) with low apparent attenuation of the yeast or high final gravity. All brews seem to be consistently coming out 5-6 points above the estimated FG.

Set Up:

3 Vessel electric HERMS 5gal (batch size) system. Mash efficiency 78% Brewhouse efficiency 66%.
SS Brewtech Brewbucket fermenters inside a temp controlled fridge with an accuracy of ±0.1 deg Celsius.
Yeast Starter temperature controlled chamber with a stir plate.
Beersmith 3 for all recipes.

After stirring my grains in to the strike water (calculated temps in Beersmith 3) the mash temp stabilizes within a couple of mins and stays constant for the entire mash. The mash temp at the top of the Mash tun is approximately 1 deg different to the bottom and remains very consistent.

My water has been tested and I treat it accordingly for each brew. Mash PH is always between 5.2 and 5.3.

I have tried different ways of pitching yeasts and different yeasts - dry yeast rehydrate, dry yeast not rehydrated, liquid yeast large starter, decanted starter and liquid yeast straight from the pouch. Yeasts have been Safale US05, Mangrove Jacks M44, WLP001, WLP090. Yeast is always pitched in to well aerated wort.

I check the gravity with a hydrometer and then recheck with a different hydrometer. For FG lately I have been checking straight out of the fermenter at fermentation temps then checking again once the beer is cooled and fined (with gelatin) then warmed back up to 20deg (hydrometer calibration temperature).

My previous system was a Robobrew and I never didn’t hit my estimated FG over 15 batches, the only thing that has changed in the process is going to a 3 Vessel system.

Here is a link to some of the sample recipes I have done - http://beersmithrecipes.com/listrecipes/143366/lasersnake

I just pulled two beers out of the fermenters and here are the numbers for them;

6Foot5 IPA - 23l Batch

6.35kg Pale Malt (93%)
0.16kg Cara-Pils (2.3%)
0.16kg Medium Crystal (2.3%)
0.16kg Vienna (2.3%)

3 Packs of Mangrove Jacks M44 rehydrated. Fermented at 19.5deg for 7 days then slow rise to 21 for 5 days.

Estimated OG = 1.062
Actual OG = 1.061

Estimated FG = 1.011
Actual FG = 1.016

And the other batch;

S Bomb IPA - 23l Batch

6.60kg Pale Malt (89.6%)
0.77kg Medium Crystal (10.4%)

2l Starter with WLP001. Fermented at 19.5deg for 7 days then slow rise to 21 for 5 days.

Estimated OG = 1.066
Actual OG = 1.065

Estimated FG = 1.013
Actual FG = 1.019

My yeast attenuation for these is around 70% which is lower than the low side of both yeasts used.

I think it is very strange that all batches are consistently 5-6 points above estimated FG. If anyone has any ideas I would be really grateful.

2

With attenuation issues, my first thing to consider is mash temperature.  Is it possible that on your old system, you were actually mashing at a lower temperature than intended, and that you are consistently maintaining a higher temperature  now?  70% ADF is not unusual for ale yeasts depending on the wort sugar profile.  (The manufacturers usually seem to state a rate that assumes a highly fermentable wort.)

3

Thanks for your reply. The robobrew is definitely a bit sketchy with mash temps and they can vary a bit, which was actually my whole reason for going to the HERMs system (I wanted consistency). I know on my new system I am definitely getting the temperature that my mash profiles in beersmith are set up for (have tested with multiple thermometers) so I would have thought the recipes I am brewing off should still be spitting out a realistic FG!

4

I know you said your hydrometer was temperature calibrated but is is gravity calibrated? Not unusual for those to be off over time. The only hydrometer I trust is my lab hydrometers and I still check and calibrate them with distilled water regularly and especially when I get an odd reading.

5

Your final gravity don’t seem all that high.  You could try a  more enzmatic malt.  Perhaps the pale ale malt you are using is lower in enzymes, perhaps not.

6

Yeah I thought this as well… I have just done a test in distilled water at 20deg C (calibration temp) and both hydrometers are good (one is actually 1 point under).

7

I have tried different brands and malts - from ale to pilsner to dark etc and all the same results!!

8

So instead of what BS recommends, try adjusting your mash temperature lower.  Only way to find out if that’s it.  Software is a starting place, actual results you experience in your brewery are your ultimate guide.

9

How long are you mashing?

10

Not giving your yeast enough oxygen will cause low final gravity.

11

Definitely agree with two pieces of advice here: Lower you mash temp a couple of degrees while increasing your mash time and increase your aeration time.

IIRC you said you are using calibrated thermometers but if not, make sure they are calibrated. One or all of those options should fix your problem.

12

How are you deciding what your FG “should” be?

13

Are you measuring the temperature of the wort immediately after it exits the HERMS coil?

14

Second that. The published attenuation ranges for each yeast strain should guide your first brew with each, but as you’re seeing now, they can’t possibly predict the precise attenuation for every ingredient/equipment/process combination.

15

Yeah but if it is recipes he has regularly brewed then he can come to expect similar results. I do recommend a force fermentation test to make sure it is your mash as opposed to your fermentation.

16

I measure my mash temp (for control) off the outlet of the mash tun as per the electric brewery design, easy to change to the inlet of the mash tun for a test though!

mashing for 60-90mins depending on recipe.

Beersmith 3 estimations

I plan on doing a forced fermentation test next brew.

Does anyone know if it is viable to do a forced fermentation test once the fermentation seems to have stopped in the fermenter… ie pull 1-2l out in to a flask, pitch some more yeast and put it on the stir plate? or would this not yield the necessary results? My theory is that would determine whether theres a fermentation issue!

17

I had the same problem until I started doing the iodine test with my mash. I was simply following recipes but I ended up having to mash 25 to 35% longer now my final gravity consistently comes out at or lower than expected

18

I recently did a forced ferment test on a porter I thought might be stuck. Rousing the yeast was just not working. I just pulled a sample, put it on a stir plate at about 80 degrees for 24 hours. No added yeast.  It indicated that I could still extract a few points.  So I roused the yeast and raised the temp slightly on the batch and it chewed out the final couple of points.

19

I favor the high mash temp theory. The one time I missed my FG by 5 points or more that was quite definitely the problem.

I monitor temp in the mash keggle using an analog Blichmann Brewmometer and a digital probe connected to a BCS-460. My mash profile is 150-152 F. The HERMS is under BCS-460 control, and is set to 153 F in summer, and slightly higher in winter. The returning wort temperature is monitored at the outlet of the HERMS coil. In my lightly insulated mash keggle I can maintain 151 F by running the recirculating pump 10 min on, and 10 min off.

Charlie

20

I’ve ound that mash temp only matters for a handful of malts.  For most domestic malts, it makes little difference.