OG affect on boil off?

[Cranny04]

Just brewed my third all grain batch. (Bitter Brewer clone from NB).

I think I was a bit cocky. In the first two batches I did I had about .5-.75 gallons an hour boil off.

Tonight I had close to 1.75 gallons an hour.

How does OG affect boil off rate?

The first two batches were higher gravity (1.078 and 1.093) this one is 1.040

Is this typical?

Thanks

 

[Brewerforlife]

Wow!! 1.75% in 60 minutes. This a 5 gal. batch, with a pre-boil volume around 6.5 Gals. I'm assuming?? To be honest, i'm not sure if boil gravity has that much impact on boil-off rate's. I have never noticed any difference's that large, in any of the batch's I ever brewed over a wide range of gravity's. I have noticed that my higher gravirty brew's come to boil temp faster than lighter one's though. Hope that help's some?? Cheer's!!!

 

[boist]

Gravity will have some effect, as the concentration of sugar will change the boiling temp a bit, but nowhere near this much. I would look at environmental factors (warmer day? Less humid, windy?) heat (more vigorous boil, burner turned higher) and cooking method (did you have the lid partially on in the last batches?)

The good news is that when you have something like that happen it's really easy to fix. At the end of the boil, figure out the gravity you do have, and add boiled water enough to dilute the wort until you reach your target OG.

 

[TromboneGuy]

While I agree it's possible that a higher-OG wort should boil off slightly slower (because the dissolved sugars would get in the way of escaping water vapor, essentially) I think the difference would be barely noticeable.