I've been noticing my efficiencies are a lot lower over the last couple years. At first I thought it was my MLT: I had built one with a cooler and a toilet line, and I figured I just crushed the toilet line. I upgraded the MLT to a Bazooka, but the efficiency stayed pretty low (around 70%). Today, for the first time in a couple years, I skipped the MLT and did a BIAB. Before I built my MLT, I was typically hovering around 80–85% efficiency with BIAB, so I was excited to calculate my efficiency. Once again, 70%.
So apparently it wasn't the toilet supply line in my MLT, nor was it my typical regimen if double- and triple-decoction mashes (single infusion today), nor was it the MLT itself.
The only other thing I can think of that's changed since I first started seeing low efficiencies is that I started mashing really cool. Today's brew I mashed at 147ºF, which is pretty typical for me. When I do decoctions, I typically do something like 122ºF–140ºF–158ºF. Sometimes I'll skip the protein rest and just do 140ºF–158ºF. Sometimes I mash out, sometimes I don't; but I always batch sparge. Honestly, I don't understand what a mash-out buys me if I'm just going to batch sparge, but that's a whole other topic.
I recognize that batch sparging isn't the most efficient, but it's not like that changed. I was batch sparging when I was getting better efficiencies.
So... has anyone heard of getting lower efficiencies at a lower mash temperature? Am I totally out to lunch on this?
The last thing I can think of is that I've pretty much exclusively been using Pilsner as my base malt over the last couple years. But I have trouble believing that's the issue.
Just to be clear: this isn't a big deal. I'm not that concerned with efficiency, my beers are tasting great and I'm having fun brewing. But it's got me wondering what's different between then and now.