Varying Evaporation Rates

[Soay4699]

Hi

I have just completed two brews one month apart. The first had an effective boil off evaporation rate of 8.4% and the second brew was 12%. The ambient temperature on both days was much the same. The SGs were 1047 and 1041. What factors could have contributed to such a large variation?

Thanks
Rob.

[Dave S]

Hi

I have just completed two brews one month apart. The first had an effective boil off evaporation rate of 8.4% and the second brew was 12%. The ambient temperature on both days was much the same. The SGs were 1047 and 1041. What factors could have contributed to such a large variation?

Thanks
Rob.

You can't really calculate boil-off in terms of percentage. It's to do with boiler dimensions among other things. For example, if you use the same boiler for two brews and the pre-boil volume for one is say 25 litres and the boil time is 90 mins, you might get a boil-off of 5 litres, or 20%. If the second pre-boil is 35 litres and the boil time is 90 mins, the boil-off will still be 5 litres - 14.3%.

[Soay4699]

Thanks Dave.

No, the equipment and volumes were the same for both brews.

[Dave S]

Thanks Dave.

No, the equipment and volumes were the same for both brews.

Boil time the same too?

[Soay4699]

Yep.

[Dave S]

Yep.

Lid on, lid off? Same degree of rolling boil? Otherwise

[Horatio]

Did you clean the elements well between brews? Sometimes a coating on the elements can limit the vigor of the boil? Although I looks like your boil off was more on the second brew? Were they cleaner second time around? Other things that can make a difference are cross draughts blowing over the boiler causing greater rates of evaporation. Hope you get to the bottom of it as it can be really annoying!

[paulg]

dont forget hops will absorbe wort during the boil did one beer have substantually more hops ?

[Soay4699]

The lid is always off and I think the rolling boil was the same as I like to see it otherwise I turn the temp up and I didn't need to.

There may or may not have been a cross draught. Good point. I will make a note next time. We need a northerly blowing to cause a cross draught in our kitchen. I have the window open and the ventilation extractor on full as a matter of course.

Hops were 58.5g and 60g.

Thanks guys
Rob.

[Beer O'Clock]

Atmospheric conditions ie. humidity levels, can also effect the evaporation.