Newbie problem - lost a lot at the boil

[Gullsrock]

Hi everyone
I have just joined the site after completing my first all grain brew. I have a 56lt electric element water boiler. My first brupak mash recipe required 27lt of wort for the boiler to give an expected 23lt for fermentation. The boiler seem to struggle to reach the final 5deg before boiling and then with a 80min boil I only ended up with 17lt. This seems an excessive loss. Most of the time I kept the boiler lid on. Is there a calculation to determine how much water I should expect to loose over a bring to boiler and then 1 hour boil period?
thanks

 

[jeffpn]

Boil off is a function of altitude, humidity, temperature, and air pressure. I think home brewers as a rule just learn to adapt to their systems over time. I usually lose about a gallon and a quarter over a 60 minute boil. I leave the lid off during the boil.

 

[Hop fiend]

Hi there, I find that I lose about 20% of my water through evaporation and then if you're using whole leaf hops allow for more because they absorb a lot of the wort. To end up with 19 litres I used to have a starting wort volume of about 25 litres. 17 does seem low unless you are using a lot of whole hops- if you are then I'd recommend using pellets instead or at least for the earlier additions, where a lot of the flavour and aroma are boiled away. Also you shouldn't leave the lid on as there are undesirable things that you want to get boiled off the wort and leaving the lid on means that they will instead condensate and drip back into the beer.
Hope this helps a bit, I'm no expert but that's what I've found!
Cheers, Ollie.
I

 

[jmcnamara]

i think it depends on how wide / tall the pot is too. More surface area exposed means more water that can boil off (pretty sure that's the right way around).

no real calculation that i know of, i just did mine by experimentation (of course brewing beer while i was doing it).

if it helps, i lose about 3 quarts per hour in my 5 gallon pot. there's also the actual degree of boiling that you use, whether its a rolling, violent boil or just a small boil. that's also going to effect your losses

 

[Ozarks Mountain Brewery]

your right on the size, I have a 20" wide pot and the evaporation is twice what yours is