Does a high OG affect efficiency?

I brewed a clone of New Hollands Dragon's milk over the weekend. It had a target pre-boil gravity of 1.069. I entered all my info into beersmith with 75% as my efficiency which is pretty normal for my set-up.

We only got 1.053 pre-boil. I ended up heating 2 more gallons of water recircing through the grain, getting runnings of 1.016 and boiled that in a seperate pot. After almost an hour of boiling we hit our 1.069 added the hops and finished our brew. Hopefully it turns out well.

The week before I made a cream ale and hit over 80% efficiency so I had to dilute my pre-boil with 1 gallon of water to hit my numbers.

Does anybody else find that their efficiency goes down as the OG goes up?

Linc

Yes, it does go down a bit but if I had to guess it would be about 1% for every 5 points over 1.040.

So, for my typical 1.045 session beer where I get 90% efficiency, a 1.060 would get me 87%. It's difficult to isolate the effects of so many variables. You could have had a termperature issue, a different crush, different sparge technique?

The reason why you lose some efficiency is due to the smaller sparge water to grain ratio. You can combat this a bit by using a slightly stiffer mash 1qt/lb or so.