Slow conversion - any suggestions?

Did my third all grain (well, threw in 0.4 lb Amber DME because it was left over) this weekend and have had ok time to conversion (40 min - 1 hr) in the past. This time it took over an hour and I don't know why. Here's the grain bill:

6.4 oz Amber Dry Extract (12.5 SRM) Dry Extract 2.52 %
7 lbs MO Pale (3.0 SRM) Grain 44.03 %
5 lbs Pale Malt (2 Row) US (2.0 SRM) Grain 31.45 %
2 lbs Pilsner (2 Row) Ger (2.0 SRM) Grain 12.58 %
1 lbs Caramel/Crystal Malt - 20L (20.0 SRM) Grain 6.29 %
8.0 oz Oats, Flaked (1.0 SRM) Grain 3.14 %

The MO was getting older and I have had slow conversions before when using it as the only malt, but adding in some 2 row pale has sped up the conversion in the past. I am using a 10 gallon Thermos mash/lauter tun and hit my temperatures (149 F) spot on. My mash water temp was 164.9 (ish) - is that causing some of the enzymes to denature and thereby the slow conversion?

Thanks in advance!

I would guess mash PH or the crush is slowing you down. What does your crush look like?
And do you by chance have any way of measuring the PH of your mash?


On another note lower mash temps will slow conversion, and yours is right at the low end.

Crush was done by LHBS. I thought it was a little too much; a bit of fines at the bottom of the bag. Husks were open, but still attached. Didn't get pH, need new strips. Using well water with no adjustments.

Would occasional stirring of the mash help? I was concerned with the mash cooling so I tried to leave it alone as much as possible.

stirring mash would help expose starches to the enzymes faster, although I would also be worried about temps dropping, especially when your are at the very low end already.
one thing I have done is stir the mash and add a small amount of boiling water to bring it back up to temp at 30 min in to the rest.

How old is your MO malt and has it been sitting around crushed for a a while? grain can last a long time if stored properly, but seams to turn a lot fast once it has been crushed.

My next suggestions would be trying the new PH strips and maybe using a second thermometer and checking several places in the mash.

or just err on the side of caution and raise your mash temp to 151-2.

Awesome info!! Thanks for all the suggestions. MO is a couple years old, stored inside not crushed, sealed but not 100% airtight. Crushed all grains the day before brewing, kept airtight till brewing.

Running 67-70% efficiency, but looking to be more efficient with my time on brew day.

Happy brewing!

Mashing at 149F will take longer to convert, especially if your thermometer is reading a little bit high. When I started mashing at 150F, I extended the mash to 90 minutes because I had a few batches that didn't convert within 60 minutes.

-a.