Valuable lesson learned about mash thickness

Over the weekend I had plans to brew an ESB. I had read quite a bit about ESB recipes in the book Designing Great Beers and decided I wanted to try and follow the recipe formulation as closely as possible. Instead of my normal 1.5 qt/lb mash thickness I tried 1 qt/lb which the book said was a traditional mash thickness for English bitters and pale ales. This was a mistake! Normally I get 70% efficiency which I have always been happy with but on this brew I got 55%! Normally I would just call this a learning experience and move on, but I have been brewing beers for a competition in the state fair and I was excited about this one. Since the beer came out at an OG of 1.043 instead of the projected 1.055 I guess could enter it as a Premium/Best Bitter instead of an ESB but I think it will be overhopped and a bit too malty. I could have avoided the overhopping as well if I would have just taken a pre-boil gravity reading. Oh well, guess I learned a couple lessons this time.

Bummer! Did using the higher mash thickness make your sparge really thin? Did you stir the sparge? (How do you sparge?)

I fly sparge all of my beers so I normally don't stir during the sparge unless there is an issue with it being stuck. All in all the sparge went normal I just wish I would have checked the pre-boil so that I could have adjusted my bittering charge. Good learning experience though.

Just thought I'd post an update for this. After some discussion with my neighbor (an award-winning homebrewer) I both stirred and vourlauf'd my sparge on my last brew and this had such an impact on my efficiency I had to trade out water for wort to get it back within style

that's weird...i did an esb clone last friday using a 1 qt/lbs mash ratio for the 1st time too. My pre boil gravity was only 2 points below the estimated one beersmith gave me so I don't think it's the mash thickness that caused your problem no ?.

I batch sparged with 2 water additions and stirred well for each addition

i've never had mash thickness mess with my efficiency. how long did you mash? the english method would have you doing a 90 minute mash and batch sparging.