Boiling and Evaporation Rate

[DavetheDog]

In the past I have always done partial boils and filled the fermentor with water to bring the level up to 5 gallons. However, I am stepping it up and going with full boils from here on out. I realize that the amount of water that evaporated will differ based on many factors such as air temp, intensity of the boil, etc.

Is it okay to add water to the boiling wort in order to maintain the right levels? Is there a good formula to help with estimating the amount of water needed before starting the boil? I will be doing five gallon boils. How do you pros handle this?

 

[JimRausch]

Yes, it's OK to add water to your BK to maintain the wort amount you want.
Everyone's boiloff/evaporation rate differs based on your heat source, pot size, elevation above sea level, relative humidity, and even other atmospheric conditions. You can get a guestimate of your own boiloff rate by boiling a 5 gallon batch of water for an hour and measuring your after-boil volume. But it will vary a little as the other conditions change. As a broad general rule, you should expect anywhere from 1/2 gallon to 1 gallon boiloff per hour.

 

[zachattack]

If you need to top up, you aren't doing a full boil. And if you're topping up, just save it for the fermenter. I can't think of any real advantage to adding it to the kettle while you're boiling, but you can do that if you want I guess. If it were me I'd just top up afterwards.

If you want to do a full boil, you just need to plan backwards from your final number. Brewing software (Beersmith) makes it pretty easy. It's going to be a guess the first few times until you figure your system out and get a good feel for your numbers.

Most of us start with a ~7 gallon preboil for a ~5.5 gallon volume into the fermenter. If you're using an outdoor burner, I'd start out by assuming 1 gallon per hour boiloff, if you're using a kitchen stove I'd assume 0.5 gallons per hour. Then assume a standard 4% volume contraction when you cool, and you can figure there'll be a little bit of kettle trub loss as well.

Let's say you have 7 gallons preboil and you do a 60 min boil. After you'll have 6 gallons. After the cooling contraction, you'll have 5.75 gallons. If you lose a quart due to trub, you'll have 5.5 gallons into the fermenter, which should give you at least 5 in the bottle/keg.

 

[DavetheDog]

If you need to top up, you aren't doing a full boil. And if you're topping up, just save it for the fermenter. I can't think of any real advantage to adding it to the kettle while you're boiling, but you can do that if you want I guess. If it were me I'd just top up afterwards.

I have thought about this but assumed it is easier to add the water to the boil kettle and cool it all at once instead of having to go through the process of sterilizing the extra water and cooling in order to add it to the fermentor.

If you want to do a full boil, you just need to plan backwards from your final number. Brewing software (Beersmith) makes it pretty easy. It's going to be a guess the first few times until you figure your system out and get a good feel for your numbers.

Most of us start with a ~7 gallon preboil for a ~5.5 gallon volume into the fermenter. If you're using an outdoor burner, I'd start out by assuming 1 gallon per hour boiloff, if you're using a kitchen stove I'd assume 0.5 gallons per hour. Then assume a standard 4% volume contraction when you cool, and you can figure there'll be a little bit of kettle trub loss as well.

Let's say you have 7 gallons preboil and you do a 60 min boil. After you'll have 6 gallons. After the cooling contraction, you'll have 5.75 gallons. If you lose a quart due to trub, you'll have 5.5 gallons into the fermenter, which should give you at least 5 in the bottle/keg.

This is the sort of equation I was looking for. I'm going to test a boil with water to see my evaporation rate but also I want to plug the numbers in to BeerSmith and a record and comparison. I've been messing with the program the last few days and it is pretty sweet, though a bit beyond my current skill level (i.e.- setting and numbers I don't understand… yet).

Thanks guys for pointing me in the right direction.

Cheers

 

[zachattack]

You're right in that it would sanitize it, but I really think there's almost no chance of contaminating a batch with clean cold regulated city water (if that's what you're using). If you're on well water, maybe it's a concern.

You enter that stuff in the "equipment profile" in Beersmith. Like I said, it'll be a guess the first few times, but once you get it all figured out you'll be good to go!