Colossal evaporation losses?

[InHopsWeTrust]

I seem to be suffering from higher-than-normal evaporation losses in the boil. I use a large (60ltr +) plastic boiler fitted with 2 kettle elements, and just did a test using only water:

Starting volume - 30ltrs
Volume at 1 hour into the boil - 25ltrs
Volume at 90 minutes - 23ltrs

That's a whopping 24% loss over a 90 minute boil. And that's without taking into account the loss to hops and trub, deadspace, wort shrinkage etc.

Is this unusual, and if so what can I do to reduce it? I have considered only switching on one element, but this will obviously reduce the boil vigour which may have an effect on hop utilisation.

Assuming I just have to grin and bear it, is it better to start with more wort or top up the fermentation vessel at the end?

 

[McMullan]

Did you overshoot your expected OG by much?

 

[ManseMasher]

If it was an agressive boil throughout, you would get a lot more evaporation than if you get a good rolling boil, then knock it down. If you work on 5% loss every 30 minutes (so in your case, 1.5 litres) you would be looking at 4.5 litres total over 90 minutes. This figure will be affected to some degree by the size/shape of your boiler (tall and narrow lose less than short and wide), and obviously your boil time. Try it again if you can, this time for 60 minutes (it's very rare these days I boil for any longer), get it to a rolling boil with both elements and then turn one off - see if that drops your evaporation at all towards the 5% figure.

 

[McMullan]

I don't see anything unusual here. If you want more volume in the FV, you could do a 60min boil. Try first wort hopping if you're concerned about hop utilisation.

 

[Fil]

FWIW I would have a similar 6-7l boil off with my old mango barrel boiler fitted with 2 x tesco kettle elements with one element off for the majority of the boil. Aiming for 23-25L final volume i would sparge out circa 30l and then wedge the tun tipping forward with a jug under its drain while the main volume comes upto the boil an extra litre or so of liquor would drain from the tun..

its all good as long as your prepared for it, all you need do is sparge off enough liquor to have enough to accommodate the boil off.

I batch sparge so its very simple, I measure the run off from the first batch, and modify the volume for the second batch accordingly

I employ the same basic procedure with the bigger set up too. With a dipstick to measure the volume in the tun, I fill the tun to a level for the first batch, and measure the volume of liquor that pours out. and that indicates how much sparge liquor to add for the second batch, If i have less than 1/2 the preboil volume out from the first batch i add more liquor for the second or visa versa