Too Dry Scotch Ale - Please help me find the cause!

[CoreyG]

Hey Gang,

So I am fairly new to all grain and I made a Scotch Ale, thinking I had my process right to end up with a fairly high FG (1.016) product. I ended up undershooting my FG getting approx 1.009. I'm trying to pinpoint the possible cause.

Recipe was (neglecting hops)
12 lbs 2 row
1 lbs victory
0.75 Crystal 80L
0.5 Roasted Barley

-Mashed at a target of 156 in 5 Gallons. Mananged to main the temp between 157 - 155 most of the time by adding boil water to my mash tun (A cooler with false bottom)
-Fly Sparged with another 6 gallons at 170 degF (note : this was temp of the water added)
-No mashout was done

Yeast was a Wyeast Scottish Ale yeast 1728. It was a VERY old smack pack (almost 1 year) that I smacked, let rise for 3 days, made a 1.2 L starter, crashed it, decanted a bit off and added another 1.2L of wort as a second step. I did this as I really wasn't sure how many cells I would have.

Fermented in a chest freezer set to 58 (beer temp was likely a few degrees hotter). Increased freezer temp to 61 over 4-5 days. Fermentation did not seem to be highly vigorous, just slow and steady.

Measured FG after 1.5 weeks and was at 1.009 for my aim of 1.016.

Soooooo, any ideas? I was thinking it may be some of the following things
1) no mashout - can this allow the enzymes to keep breaking down my sugars pre boil? I am really not clear on the mashout effect

2) Way too much yeast? - It really is hard to be sure how much yeast I pitched. With such a old pack and cool fermentation temp I wanted to be sure I had enough

3) I didn't measure beer temp clearly so is it maybe that my beer really was more than a few degrees over freezer temp

Any opinions would help. The beer is fine but I feel I missed my target by ALOT and want to make sure there is nothing in my process I am doing horribly wrong.

Thanks for the advice in advance!

 

[doug293cz]

I don't think wither 2 or 3 are likely to cause over attenuation. Fermentation stops (for "normal" gravity beers) when there are no more sugars of the type that yeast can metabolize. For high gravity beers, fermentation can stop earlier if the yeast get too stressed by high alcohol levels (but that causes high FG.)

Lack of a mash out could be the issue. Alpha amylase will continue to work making more fermentable sugars until it is all denatured, or all that's left is limit dextrins (branched sugars too small for the enzymes to work on.) It takes about 10 minutes with the mash temp at 170°F to denature the alpha amylase, but 170°F sparge water will not get the mash temp that high. Best to add boiling water to raise the temp for mash out. Most beer calculators will tell you how much to add based on your batch parameters.

Another possible cause could be a thermometer that reads high. This would cause your mash temp to be lower than you intended, which tends to create more fermentable (higher attenuating) wort. What type of thermometer are you using, and have you calibrated it?

Another possibility is that you picked up an infection. Bacteria can eat larger sugars that the yeast can't, which will lower the FG.

Brew on

 

[CoreyG]

Hmmm good point... I'm using a thermapen that's a handful of years old. Definetly have not done any calibrations since the original it was received with. How often do you check the calibration your thermometer?