Unexplained drop in efficiencies- HELP!

I have been brewing AG for about a year and a half and I have been using the same equipment the whole time (cooler MLT, 40qt pot). For the first year I was getting efficiencies in the high 70's and low 80's. For about the last 8 batches, I am struggling to hit 70%, and I have NO clue why! I can rule out my LHBS's grain mill, i have a friend who buys from the same store and he is hitting high 80's. The only changes to my equipment are I replaced my immersion chiller with a CounterFlow and my braided hose has gotten a little beat up, so I have to be extra sure i vorlauf.

Can anyone come up with any reasonable theories as to what is happening? All of my process has been consistent, and I've been real meticulous in making sure i'm hitting mash temps and holding them throughout the mash.

could be a few things, your malts could be older then what your buddy purchased, and the diastic power is less, its possible, also you could have cold spot in your mash, thats he most obvouis. other then that the manifold might be the issue, do a iodine test at least 3 times during your mash to rule out stale malts.

My friend often buys grains the same day I do, so i think we are using the same age grains. I've never done an iodine test, but I've read about it and i'll give that a shot. I tend to stir pretty well when doughing in, so unless a cold spot randomly creates itself, its pretty safe to say its all consistent. I'll try replacing the manifold and see if that improves anything.

If your friend isn't using the same process or equipment as you, the crush from the LHBS might work fine for him, and less fine for you.

I wouldn't rule out the grain mill based on what you've said, it seems to be a potential variable in your process.

Your water could have changed too(no mention of it, so I have no idea how likely that is).

Your thermometer might need recalibrating, they sometimes creep out 10-20 degrees or more, or it could be outright failing.

BigRob said:

If your friend isn't using the same process or equipment as you, the crush from the LHBS might work fine for him, and less fine for you.

I wouldn't rule out the grain mill based on what you've said, it seems to be a potential variable in your process.

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Yeah, his process might be that much better than yours, theoretically, anyway. I'm not trying to be insulting, just saying you can't rule that out. Has his efficiency dropped at any point?