Missing OG

[Diesel48]

I have been brewing for about 2 years now. I switched to all grain about one year ago. It seemed like things were going great until recently. I seem to be missing my OG all of the time, it has happened in the last 3 all grain batches. One thing that did not help is that my grain was crushed at 3 different places.
I batch sparge.

1. Chinook IPA purchased from Northern Brewer. The crush seemed pretty course. I was expecting 1.056 and got 1.044. Do to this happening would I expect the yeast to stop at the same point as if the beer was 1.056 or will they finish drier? If my readings are correct it finished at 1.002. That seems pretty dry and I did not expect that to happen.

2.Orange Coriander Pale ale. Purchased from a LHBS. OG was supposed to be around 1.056 ended up at 1.049. I thought the crush looked a little course as well. This one was supposed to finish around 1.014 but went to 1.011.

3. Brewed a nut brown on Tuesday. I picked up the grain from a second LHBS. The grain appeared to be crushed very fine. There was a lot of flour. I liked what I saw. I had my first stuck sparge. Thought it might happen as it was the slowest drainings I have had before. The OG was supposed to be 1.053 and I ended up at 1.061. I was using my new blichman burner and 15gallon pot. I started at 7 gallons and boiled down to 5. That might have been one reason for the high OG. Would I expect this beer to finish around the expected 1.013 or if my OG is higher it usually finished higher?

Just wondering how I can hit my OG's better. Is it a sugar extraction problem or a boiling off problem? I was hitting everything great, or so I though for awhile.

 

[hopsalot]

Start with a consistent crush and a focus on volumes.

 

[waldoar15]

Yeah, you need to work on consistency first. Crush, mash and sparge process and since you have a new 15 gallon BK and new burner, boil off rates will be different than the past.

A BK with a large surface are will generally tend to have a higher boil off/evap rate than say a turkey fryer pot with a smaller surface area.

 

[Diesel48]

What about the fermentation attenuation? If a beer is supposed to have a higher OG than what I get out of it will the FG end up lower or about the same as it should have been? If I would have started with 7.5 gallons I probably would have been alright. Is it ok to boil off 2 gallons an hour? Seem like a lot.

 

[goldmind31]

I quickly came up with this a 1.070 o.g. with 75% apparent attenuation strain results in 1.018 f.g. while a 1.060 o.g. same strain would be 1.015 f.g.

Pretty much less sugars to convert will result in less sugars at the end of fermentation given all variables are the same.