If you would like to pasteurize a large amount of substrate you have two options to go. Electric or gas.
Gas is simple, just find a stainless steel vessel or food grade 55 gal steel drum, place some bricks to prop up the drum over a turkey burner or wood fire and heat the water to 160-170F then add your straw in some sort of mesh bag.
Ive been using a 1500w element on 55 gal drums. Its handy because any 15A outlet can run this. It takes about 5-7 hours to heat 40-45 gallons to target temp.
A 5 gal bucket
55 gal food grade plastic, steel, or stainless steel 30-55 gal drum (used or new)
275-300 gal water tote
Place a dab of RTV then some heat shrink over the metal sensor to wire connection on the temp probe, this will stop water from ruining the probe. In the event water gets into the probe simply place the probe in your oven at 350F for an hour or two. This will boil off any moisture.
If you're using a 55 gal drum or larger will want a drain at the bottom so also get,
Any length of garden hose to route the drain water to somewhere it wont kill grass and plants due to scalding hot water
1. Drill a hole in the back of the PVC cap and install the cable gland with some epoxy, there wont be much space for the lock nut.
2. Pull the wire through, wire up the element using crimp connections including a ground wire ran through a hole then attached to the hex part grounding the element and effectively the entire vessel. A screw or rivet can be used to hold the ground connection in place.
3. Glue or epoxy the PVC cap to the element and allow the epoxy/glue to cure
4. Drill a hole as low as possible in your drum, tote, or pail so the heating element threads can pass through. If using a plastic drum just drill and tap the plastic.
5. Place a locknut on the inside to hold the element in place, not if you're using a tapped plastic drum. Use the stock O ring as a seal against the outside of the container, you shouldn't need any thread sealant.
6. Drill a hole for the drain as low as possible for the bulkhead fitting or drill and tap your drain hole if not using a bulkhead fitting
7. Attach your drain valve assy to the bulkhead fitting or NPT close nipple
Shown here is a solenoid valve for my automated rig, this is where you would place the ball valve
Plug the unit in and set the temp alarm to your set temperature, you will need to manually unplug the unit when done. A blanket or a thin layer of foam insulation will help with keeping the heat in. Here i used some R3 foam board, 2 cans of great stuff and some saran wrap to seal it all up.
You can also wire up a temperature controller to more accurately ramp and hold the temp until you're ready to use.