Evaporation %

calnand

Was just curious as to what my evaporation % was for my boiler was, and ran a test to find out. I put 10L into the boiler starting off at around 16°C. Reached ~100°C after 40mins, lost very little water in this time. Then put on a timer for 60mins. Came back when the hour was done and there was only 6L left in the boiler. So does this mean I have a 40% evaporation rate, most recipes I've seen online tend to use 20% as the standard.
I was wondering is this normal when its just water in the boiler? and would adding the malt extract and other fermentables to the boiler bring this % down to 20%.

Or does it really matter?

mayto

A 10% evaporation is usually close enough for initial 26L boil volume and one element. To end with 23L in your boiler start with about 26L pre boil volume.

rubadub

Once you hit boiling point then the rate of vapourisation will depend on your element power, you will also have some natural heat loss from your tank to the surrounding air.

If you are boiling an egg you should have the power up full at first, then once boiling you back off the power as you just want to maintain it at 100C, it can go no higher so any energy you put in will just boil off water.

Some people will have 2 elements, one to speed up the initial boil and one to keep it ticking over once boiling.

If you only have 1 low power element it will take ages to get to boiling point, a lot of the power will be wasted to the surrounding air during this time too.

twerg_85

The amount of evaporation is probably going to be closer to fixed, than a %, i.e. if you started with 20L you should end up with closer to 16L (same 4L loss) rather than 12L (40% loss).

F.

Carawaystick

The head on wort will affect the evaporation rate probably lowering it some.

A wider kettle will have a higher evap. rate

If you insulate your kettle during water heating, loosening or removing some will reduce your evaporation as heat will be lost through the sides of the kettle

calnand

Thanks, I'm hoping to do another brew shortly, I bought the ingredients today so should be delivered Friday hopefully. I might try insulating the kettle, I brew in the kitchen on a granite counter and the granite gets extremely hot when boiling, would the foil insulation be suitable for the sides off the kettle.

rubadub

twerg_85 wrote: »

The amount of evaporation is probably going to be closer to fixed, than a %

correct

Carawaystick wrote: »

A wider kettle will have a higher evap. rate

This is true -at much lower power or no power at all, e.g. 10ml of water on a dinner plate evaporates off faster than 10ml in a teacup. But in this scenario the bulk of the vaporisation is due to the element power. We are really talking about vapourisation here, rather than evaporation.

calnand wrote: »

I might try insulating the kettle

The previous poster was saying insulating the kettle will result in more liquid being boiled off. The sides will give off a pretty constant heat when boiling, say 200W, if your element is 1200W then really only 1000W is going into boiling the liquid. If you insulate the sides it might only give out 50W, and so now 1150W is going into boiling the liquid -so more liquid is boiled off during the same time.

You could raise up your boiler on a wooden chopping board or similar wood, or a bunch of towels. I used to do boiling in a cold room so it just acted like a radiator.