Head space in a keg

[jon1163]

As some of you know I run a 15 and a half gallon keg boiler on a pot still. My heating elements are covered when I have about four gallons of liquid in the boiler. I generally run about 10 to 12 gallons of wash but I'm looking to do several smaller batches. As long as my element stay covered is there any detriment, taste or otherwise, to running smaller batches and having the extra headspace?

[zapata]

nope, no problems at all

[Saltbush Bill]

Probably of more benefit than anything ..........most of the big still manufactures produce boilers that allow for plenty of head space. The boiler is usually quite a bit bigger than the capacity that they quote.

[Mike6090]

How small do you want to go? Your “15” gal capacity is total volume. Operational working volume will be less than that. 10-12 gal is pretty sweet and should suit the process well. Let’s say you run a 15% wash of 10 gal. When done you might have 8.5 gal of spent wash. At 5 gal you will have 4.25 gal but maybe less and risk burning your element. A safe minimum wash size then might be 6-7 gal depending on how close you want to go. If you have 6 gal fermenters that’s cool but lots of folks use food grade buckets and they won’t hold 6 gal. You can add some sort of inert volume displacement material to your boiler. Say a gallon of clear glass marbles. That might let you run 5 gal with a safety margin.

Good question.

[Mike6090]

Oh keep in mind your elements are designed to heat x number of gal of wash and run well. Half that and you likely need to half the power supplies to them once the boiler comes up to temperature ie durning the run. At full power and half the design volume you can overdrive the process and get poor cuts due to higher than optimal flow.

[zapata]

I'm not sure I've ever run into that. To me power input has little to do with boiler size other than the obvious how long it takes to heat up. Eg; when using the same still head, I use the same power to strip from a 30 gal boiler as I do from a 12 gallon boiler.

To a much greater extent the element design is matched to cooling capacity of condensers and vapor rate through columns/risers than boiler volume.