Following a few requests on how to make a mash tun for home brewing purposes, I've put together some instructions on what mine looks like. The model described here consists of an insulated cool box (picnic box) fitted with a slotted "manifold" through which the sweet wort drains. I claim no originality for the design, I believe that something similar may have been described in a Dave Line book. The version built here uses bits that came to hand, I'm sure that readers will be able to assemble something similar without difficulty.
If it sounds a bit complex, the basic concept is simple - a slotted rectangular "ring" of copper tube is plumbed into the rear of a tap fitted to a picnic box.
The picnic box is a standard polypropylene job: you need one with a smooth side to help fitting the tap.
The tap is the usual Waddington & Duval drum tap - white insert.
Cut a hole in the side to fit the tap: I used a 1" wood borer and enlarged the hole with a half-round file. Tighten the tap into place with the washer on the inside. The tap should be a close fit in the hole so as to give as much support as possible when the backnut is tightened.
The tricky bit is getting a reasonably secure connection from the drum tap to the manifold. I found that there wasn't enough thread visible on the back spigot of the tap to get a connection to a 3/4" BSP fitting, but the solution I came up with seems better on reflection. I found that a 3/4" BSP washing machine tee-piece connector could be cut up so that there was enough unthreaded length to slip into the back of the drum tap, leaving the male tread sticking out into the inside of the picnic box. This insert was a snug fit into the drum tap which enables me to quickly remove the manifold assembly for cleaning.
The 3/4" male BSP connector on the insert is connected in turn to a plastic BSP to 22 mm pipe adaptor - the 22 mm connection being a push-in type. This then goes into the 22 mm socket of a 22mm x 15 mm x 15 mm copper Yorkshire fitting (the 22 mm leg being on the short side of the fitting) via a short piece of 22 mm copper tube.
The two 15 mm legs of the tee piece are soldered to two lengths of 15 mm copper tube which almost reach to the corner of the picnic box. Three further lengths of 15 mm tube are connected to these using right angle capillary fittings to form a rectangular loop. The latter capillary fittings are the end-feed type with no solder - the copper is a push-fit into them to enable easy dismantling for cleaning. If at any time they get loose, they can be "adjusted" gently with a hammer to grip more firmly.
The rectangular loop of copper tube is sized to give about 1/2" clearance all round. It is held in place loosely during mashing by placing pipe clips (as used for fixing pipes to walls) onto the tubing on three sides to stop it rattling too much. In practise, it is very difficult to make it fall apart unintentionally - this requires the whole assembly to be swivelled around the two pieces of copper tube soldered into the tee-piece, and the insert to be pulled out of the back spigot of the drum tap.
All lengths of copper tube are perforated by cutting halfway through crossways on the underside with a "junior" hacksaw. The cuts are spaced about three or four to the inch.
Ifor has pointed out a simpler way of connecting the loop to the tap. He has discovered that a barbed tube connnector (the sort that you push a piece of polythene tube onto) as sold for 19 mm tubing fits snugly inside the back of a W&D tap. Furthermore, a piece of 15 mm copper tube is a reasonable fit in the inside of the tube connector. Thus, instead of the arrangement I have just described with a 22 mm x 15 mm x 15 mm tee piece, you could use a 15 mm equal tee going into a stub of 15 mm copper which would fit into the tube connector (which is better cut in half - make two tuns!) which in turn is pushed into the rear of the tap.
The whole assembly droops resting on the bottom of the picnic box. It's improved my mashing no end, and I know of three copies which have been made. During mashing I stand it on top of the Aga to reduce heat loss: a thermistor probe stuck into the mash with the cable looped out under the lid indicates that the temperature in the centre is stable to better than 0.3 C over 90 minutes. I haven't checked the temperature change without standing it on the Aga, but my mates don't seem to have any problems just leaving theirs on the kitchen work surface. I usually leave the mash water to stand in the picnic box with the lid on for about 10 minutes before adding the malt to let the temperatures equilibrate. This seems quite important in terms of hitting the right temperature when the malt is stirred in without needing to adjust excessively with kettles of boiling water.
As an example of the temperatures I find work, for my normal "cooking bitter" made with 3.5 kg of malt mashed in 9 litres of water I add hot liquor to the tun at about 79 C. This settles after ten minutes to about 72 - 73 C, which after adding malt comes to spot on 65 C.
Last Updated: 11 September 1996
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