[metaltec15]

I have been doing All grain for quite some time, but less frequent as I would like.  The last batch and the batch I brewed today both hit the pre-boil gravity, but missing my original gravity at the end of brew by 5 or 6 points.  Nothing mechanically has changed with my system.  The only thing I can think of why I am missing my gravity is that my boil off rate has just a little.  My volumes seem to be very close to what they should be.  Any ideas on what is going on with not hitting the SG.

[blair.streit]

Yeah if you're not adding anything to the kettle then a lower boil off rate is the only thing that comes to mind to explain a lower than expected post-boil gravity having hit your pre-boil.

If you use propane something could be decreasing your output (i.e. spiders in your lines). Also even under "normal" conditions, I see a fair bit of variation in my boil between humidity changes and the difference in pressure between a full tank and.an almost empty one. I tend to judge my target boil vigor visually rather than targeting a specific point on the dial. That at least helps with the propane variation, but not the humidity.

[brewinhard]

I have been doing All grain for quite some time, but less frequent as I would like.  The last batch and the batch I brewed today both hit the pre-boil gravity, but missing my original gravity at the end of brew by 5 or 6 points.  Nothing mechanically has changed with my system.  The only thing I can think of why I am missing my gravity is that my boil off rate has just a little.  My volumes seem to be very close to what they should be.  Any ideas on what is going on with not hitting the SG.

I assume you mean you are getting 5-6 points below your target OG?

[denny]

Maybe all you need to do is adjust the recipes for the efficiency you actually get.

[metaltec15]

The wind was variable on brew day and at times it was pretty gusty.  i tried to make adjustments on the dial as conditions changed to keep my boil at a nice rolling boil and not jumping out of the pot at me.  I was using a full tank of freshly filled propane. 

Adjusting my efficiency might be the fix for this one.  Knowing my luck these last two brews were a fluke and then I will adjust and I will be on the high side.   

[brewinhard]

Adjusting my efficiency might be the fix for this one.  Knowing my luck these last two brews were a fluke and then I will adjust and I will be on the high side.   

Try shooting for the middle range between and see where it gets you.