Bimster wrote:I also end up with more boil off than Beersmith predicts. To be honest, it is slightly annoying but the beer is usual ok so I just roll with it.
Nailing the exact amount would be nice but I guess my boiler is more vigourous than it needs to be once it hits the rolling boil. Not bad for an 1800 watt element!
I would advise not using beersmith as it is pretty difficult to get all the settings and parameters in line with your actual set up
until you actually know what to expect from your set up. In my experience this means making incremental tweaks and changes to the settings, but still always finding myself not hitting the numbers exactly as planned; and when you mess up volume or gravity or both, your bitterness calculations will be out too.
As soon as I started doing all the brewing calculations on paper I started hitting the
exact gravity and volume, and the only time I am ever slightly out is when I have underestimated efficiency (on high gravity beers usually). The value of this can't be overestimated IMO, as you can then work solely on tweaking your recipes, confident that nothing weird or unexpected will happen.
I now use beersmith purely as a recipe database.
All the calculations are well set out in Designing Great Beers by Ray Daniels which I can lend to people. The hop utilisation calculation is closer to Tinseth rather than Rager, but this doesn't matter too much as long as you're consistently using the same utilisation factors (so you get to know what 40 IBU in a 1.054 beer tastes like). The book is pretty dry though, and sent me to sleep the first few times I tried to read it.
I can show anyone who is interested the different formulae and how to use them, but in my experience the first one to get to grips with is hitting target volume.
First up is your boiler calibrated for volume? It needs to be.
Work backwards from your target volume in FV:
Say 20 litres
Add a couple of litres for hop and trub loss (give or take depending on the amount of hops you use):
22 litres
Divide by 0.96 for cooling shrinkage:
22.92 litres
Then it gets a bit tricky as you need to initially make a guess as to your boil off rate. 10 % per hour is a good place to start, though I find mine is usually 11.5 %. If you get it wrong the first time, then tweak it subsequently until you're bang on.
Anyway, to get the evaporation factor:
1-(boil off rate/60 x boil length)
So with 10 % boil off and a 75 min boil:
evaporation factor = 1-(0.1/60x75) = 0.875
Then, remember your
22.92 litres? Divide that by your evap factor:
22.92/0.875 = 26.19 litres
So pre-boil volume = 26.19 litres
Trust me, start off doing this and you will soon get to know your kit inside out.