Evaporation

[Brewski82]

I am going all-grain soon, and have the setup ready. Would it be an advantage to test out my kettle's evaporation rate with water before brewing my first batch?
This way it will be easier to calculate my pre boil volume right?

 

[The Pol]

You can... most people generally see a 15% evaporation rate with a rolling boil, over the course of an hour. I generally run off 6.5 gallons and end up with 5.5 gallons after the boil (60 min). Another great way to do this is to actually mark your stirring spoon (if you have one) or the inner edge of your boiling kettle so that you can actually measure what you have left in your kettle while it is boiling.

The Pol

 

[The Pol]

Also, as far as preboil volume, you should run it off until you near 1.010 but watch your PH as well, dont let it get too high, above 5.8.

The Pol

 

[grnich]

I leave the cover on the pot during the boil and my boiloff rate is only .5 gallons in an hour. Makes quick a difference. The first AG I did I was expecting to lose a gallon and lost half of that. Made for a much lower SG and screwed up my recipe.

 

[Beermaker]

I usually get about a gallon per hour boil off rate. But if I use a fan directly to my wort, I get closer to 1.5 gallons per hour, and it helps prevent boil over. Well, the fan and a false bottom in my boil kettle do.

 

[rod]

I leave the cover on the pot during the boil and my boiloff rate is only .5 gallons in an hour. Makes quick a difference. The first AG I did I was expecting to lose a gallon and lost half of that. Made for a much lower SG and screwed up my recipe.

i thought leaving the lid on during the boil was a bad idea as it doesn't let a certain chemical escape(dimethly sulphide- the "cooked cabbage" one)
from a previous post
DMS is continuously produced in the wort while it is hot and is usually removed by vaporization during the boil. If the wort is cooled slowly these compounds will not be removed from the wort and will dissolve back in. Thus it is important to not completely cover the brewpot during the boil or allow condensate to drip back into the pot from the lid. The wort should also be cooled quickly after the boil, either by immersing in an ice bath or using a wort chiller.

 

[Walker]

i thought leaving the lid on during the boil was a bad idea as it doesn't let a certain chemical escape(dimethly sulphide- the "cooked cabbage" one)

Yup. This is the reason to not cover the kettle during the boil or the chill.

However, if grnich isn't picking up DMS in his beers and his process is working, more power to him.

:rockin:

 

[grnich]

Yup. This is the reason to not cover the kettle during the boil or the chill.

However, if grnich isn't picking up DMS in his beers and his process is working, more power to him.

:rockin:

Hmmm, you're making me think. I don't taste any off-flavors in my beers that I know of. The reason I leave the cover on is because I have a hard time keeping a boil with the cover off. It's a loose fit, though, and I still get lots of steam escaping, albeit half as much as with the cover off. Come spring, I'm getting a turkey fryer and will leave the stove behind forever!

 

[Indiana Red]

Wowo, what a bunch of great ideas.
I get about 1.25gph but my climate is typically very low humidity which can make a difference.
Also, I never quite understodd the % boil off calculation. If I have 8Gallons in my kettle, I will loose a little over a gallon in an hour. If only 3 gallons is in there, I still lose about the same in the same amount of time. At least I think.
I am pretty sure that if it is an inch deep in there when I start, there will be more that 85% if an inch (7/8") in an hour. Never made sense to me.
The fan on the boil. Never thought of that. Nice.

 

[david_42]

The boil off rate can certainly be calculated in gallons per hour and that is probably more useful to the homebrewer as it will be relatively constant for any brewing setup.