Double Boilers?

[Professor Green]

Has anyone here run a double boiler rig?

The reason I ask is that I am making absinthe which involves macerating herbs in 85% alcohol then distilling the whole lot in a pot still to extract the alcohol and oils. I had reasonable success with my first run by filtering the macerate through a hops bag and suspending that in the pot however, due to the very fine nature of some of the botanicals which are actually powdered, I still manage to get some scorching as they ran straight though the bag. Whilst it didn't really affect the flavour too much I would rather this didn't happen. I did think of suspending another pot inside the boiler to hold the macerate but I suspect that may not work due to excess steam from the boiling water - it may also be a dangerous thing to do for all I know.

Any one have any suggestions as what I can do here? Are there any commercially available (in Aus) double boiler alembics? I know they are available in NZ but getting one to Aus may be problematic customs wise.

Cheers,
Prof. Green

[RefluxEd]

I use a modified 20 quart pressure cooker in a 20 litre saucepan. There's about a 25mm gap all around for the water to boil in.
There's a 1 inch adapter screwed in the middle of the lid with a 1 inch copper riser going up about 300mm to an elbow and out to the leibig condensor.
With this size you must limit the amounts down to about 8-9 litres of 85% with the botanicals and 8 litres of water. If you go over this you end up with a plug of dried botanicals in the cooker and don't get the oils at the end to put into the next batch.
With this setup you get around 7-8 litres of absinthe bleu at 75%. :handgestures-thumbupleft:

[Professor Green]

Pressure cooker inside another pot eh, hadn't though of that. I'm looking to do much smaller runs than you at the moment whilst I sort my recipe out (2-3l) but I like the concept. I wonder if I can make something that would allow me to use the t500 boiler and the alembic dome/condenser I already have in a similar fashion.

Cheers,
Prof. Green

[RefluxEd]

What about a saucepan that fits inside the T500?
Cut the handle off, put a wire stand-off underneath and maybe something to centralise it in the boiler.
As there will be water with a boiling point of 100C around the saucepan and your spirit and botanicals in it with a lower boiling point there will be no interaction between the two liquids until you get very late in the run when you'd probably stop it anyway.

[Professor Green]

Well that is what I initially considered doing but then I thought the steam from the boiling water would mix with the alcohol vapour and screw it up. Wouldn't the water come to the boil quicker than the macerate could be distilled?

Cheers,
Prof. Green

[RefluxEd]

It would be a near thing, you'd have to heat up the unit very slowly. The only way to know is to experiment and give it a try. :-B

[Professor Green]

I guess as a starting point I could make a power controller for the element to slow the heat up time down.

I reckon your initial suggestion of sitting a smaller pot within a larger pot of boiling water is going to be the best option in the long run. I already have a 30cm pot that my existing alembic dome and condenser fits perfectly, I just need to find a way to clamp it in place, a larger pot for the water and a heating element and I'm set.

One more question on your pressure cooker set up if I may. Do you find that you need to top up the water in the bottom or is the action all over before it has a chance to have boiled off too much or do you control the heat to keep it at a simmer?

Finally, can anyone recommend me (via PM) a sparky in Melbourne's west?

Thank you for your suggestions RefluxEd they have been most helpful.

Cheers,
Prof. Green

[MickC]

Was just pondering and thought what about instead of water what about a hot oil bath with your boiler in that ?

[RefluxEd]

I guess as a starting point I could make a power controller for the element to slow the heat up time down.

<snip>
One more question on your pressure cooker set up if I may. Do you find that you need to top up the water in the bottom or is the action all over before it has a chance to have boiled off too much or do you control the heat to keep it at a simmer?
<snip>
Cheers,
Prof. Green

You could get away with no top up if done slowly, I have only required to do this once in a run but was probably running a bit fast.

[Professor Green]

That's pretty much what I thought.

Cheers,
Prof. Green

[Professor Green]

Was just pondering and thought what about instead of water what about a hot oil bath with your boiler in that ?

Oil would certainly hold the heat without boiling but I reckon that could get rather messy and could possibly be a little dangerous.

Cheers,
Prof. Green