Double Walled Distillation Boilers

Joe writes:
    Single walled bottom still designs are good only for sugar mash distillation and unsuitable for distilling thick mashes or preparing absinth. With direct heating, and especially with internal heating of keg, local overheating can (and will) occur for highly viscous mashes (grappa, plum, apricot, apple, quince, etc.). The decomposition (burning) of mash produces a terrible taste and smell, hard to remove. If you try to polish the distillate, fruit taste and smell will disappear first.

    It is a rather easy task to transform a keg to a safe, dual purpose, water bath type double bottom boiler. Generally a keg consists of the vessel itself, there is a lower and an upper skirt. Skirts are most cases welded to the vessel. If you close the lower skirt with a flat head (e.g. a 1/16"ss plate) and patch the went holes, you get a lower vessel for the water bath. For joining the head TIG, MIG or stick welding is best, but brazing is also possible. Patching the went holes you may use welding or brazing. Drill a ¼" hole on the side of lower vessel. Attach (braze) a ¼" pipe to the hole and have it run vertically to the top of the keg. Lace it through the upper skirt through a went hole and bend it to vertical position. Attach a proper safety valve (e.g. a weight type for pressure cooker ) on the upper end of pipe. When selecting the type of safety valve you have to consider the danger of implosion during cooling. At 180 degree from the ¼" pipe (on the opposite side of lower vessel) drill a ¼" hole and braze over the hole a ¼"nut. Close it with a heat resistant gasket and a ¼" flat head screw. This will be the bleeder. Perform bubble test on joints.

    Filling: Remove the weight of safety valve, screw off the bleeder. Fill up the lower vessel through the safety valve body and ¼" pipe using a plastic hose. When water starts to flow from bleeder, stop filling, reinstall safety valve weight, fasten bleeder screw. During distillation process water bath temperature will be in the lower vessel slightly above 100 Celsius due the minor overpressure, but this has no detrimental effect. Check water level in lower vessel each time before using, by shaking the keg. According my experience refill is rarely needed. Annually descale lower vessel with vinegar. In case of using the keg in cold climate avoid freezing the water.

    I have been using this construction for years without problem, quality of distillate improved dramatically. Of course, if you distil thick mashes a greater opening ( min. 6" diameter) is needed to fill and clean the keg.


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