Drastic Drop in Efficiency...?????

Here's the deal:

I mash for 1 hour, no mashout, I use 5.2 stabilizer, I batch sparge in 2 equal amounts and I consistently average 85% lauter/sparge efficiency.

Today I brewed a Dubbel and I only got 68% efficiency. I used a malt, Franco-Belges Pilsen, that I have never used before as my base malt, and I didn't preheat my mash tun well enough because my mash temp went from 152 at the start all the way down to 145 at the end. It normally only drops 3 degrees or so.

Speculate with me fellas - what could be the culprit? The Franco-Belges Pilsen, drop in mash temp., a combination of both? I don't think the drop in mash temp should even affect efficiency, just fermentability of the wort, but I'm not an expert so I can't be 100% sure.

Did you crush the grains? Was there any difference in the milling for this batch?
mark
www.backyardbrewer.blogspot.com

I get them already crushed from Northern Brewer, I didn't really notice much of a difference though.

Temp can effect conversion and that will effect BHE. I suspect this is just a bigger grain bill than your used to.

Malticulous said:

Temp can effect conversion and that will effect BHE. I suspect this is just a bigger grain bill than your used to.

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No, I've done 15 lbs. before, this one was 10.875 lbs......how would the size of the grain bill affect efficiency?

It's about the total water to grain ratio.

The biggest contributor to a drop like you experienced is in the grind. Although the grain may have looked the same I would bet on some minor changes in the mill gap at the supplier since the last time you brewed. I could be wrong but....
mark
www.backyardbrewer.blogspot.com

mbird said:

The biggest contributor to a drop like you experienced is in the grind. Although the grain may have looked the same I would bet on some minor changes in the mill gap at the supplier since the last time you brewed. I could be wrong but....
mark
www.backyardbrewer.blogspot.com

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Yeah, and to be honest I didn't even look that closely or anything. I always order everything from Northern Brewer and have never had any issues so I really wasn't paying attention to the crush. Oh well, I guess the bright side is I don't have to worry about it finishing where I want it to.