[jamminbrew]

So after mash and brewing yesterday, I'm cleaning my equipment, and realize the thermometer I use for mashing is reading 13* too high.  Which means my mash wasn't at 150* like I thought, but more like 140 or lower.  I was wondering why my efficiency was down. Should've had a 1.090, wound up with a 1.070.   
I mashed with 12# Belgian two-row, 1 # Caravienne, and 1/2# aromatic. (Also added 2# turbinado in boil)  I mashed for 90 mins at what I thought was 150*, but like I said, was probably 140* or lower.
What are the possible effects on this batch of beer? What should I expect it to taste like?  Any help is appreciated, and thanks!

[nateo]

If you mashed lower than you intended, you probably got a more fermentable wort. The only way to know that, though, is through the forced ferment test.

http://braukaiser.com/wiki/index.php/Fast_Ferment_Test

Barley starch doesn't fully gelatinize below 149*, IIRC, so that may explain your poor efficiency.

[bluesman]

Likely a highly fermentable wort with only some degree of conversion at 140F. It takse longer to convert the starches to sugar at 140F. Mostly Beta Amylase active at the lower saccharification temps.

[jamminbrew]

Well, it is a Belgian style tripel, and I like to mash this at lower temps, (148-150*) to utilize the beta amylase that's appropriate to the style. Thanks for the info, and the graph I printed for future use!

[malzig]

Thanks for the info, and the graph I printed for future use!

Or you could (and should) buy How to Brew by John Palmer, from where that chart was copied.

[smoga]

The beer will be fine. It might be a bit dry given the sugars. I had the same issue with thermometers and I now check them the night before (@ 150F) using a lab thermometer.

I have an issue is with that pretty graph.
My understanding is that the enzyme activity ranges are much more like bell curves (that overlap) rather than distinct boxes where the one enzyme shuts off and the other takes over. If you keep in mind that the boxes represent "peak enzyme activity" and that you get some Alpha Amylase activity in the Beta range and the reverse; then it's closer to how the enzymes are really behaving in the mash.