I believe a gentle mixing process helps loosen starch particles from grains making them more available to hydrolyzing enzyme action. In spite of clear evidence from commercial practice where mash mixers are used, there are certain problems I have found frequently associated in homebrewing literature with a stirred mash. Most often these problems relate to destruction of grain husks due to excessive mixing, mash hot side aeration (oxidation) and scorching of grains when the mash is heated by direct flame. However, all of these problems can be easily avoided.

To prevent scorching of grains it is important to add heat to the system in a controlled manner. The best way to do this is by applying heat indirectly, over a large surface. One way to do this is with an external electric heating jacket. In electric heaters, watts per square inch (WPSI) provides a measure of how gentle heat is applied to the system. In the world of electric heaters as used in RIMS systems anything around 50 WPSI qualifies as ultra low watt density (ULWD). Using a heating jacket, watt densities of 10 WPSI or less are available.

Problems regarding the destruction of grain husk and hot side aeration are directly related to the type of impeller/paddle used, impeller RPM and its location in the mash vessel. In terms of mash mixing, good performance means circulating the mash throughout the vessel fast enough to prevent stratification of temperatures but not aggressively as to cause splashing of wort and damage to grain husks. To achieve this, the mixer impeller needs to be located near the bottom of the mash tun, slightly off the center, and the blades need to be at least slightly pitched to force top to bottom circulation. An impeller speed less than 60 RPM is ideal.

This project is an electrically heated jacketed mash mixer tun incorporating some of the ideas mentioned earlier. For its use, the process starts by heating the strike water by direct flame at the bottom of the mash mixer tun. This mash mixer tun is a stainless steel pot retrofitted with a false bottom-dip tube assembly and a mechanical mixer in it. When water has reached the desired strike temperature, the propane burner is turned OFF and the mash mixer is turned ON (the mash mixer stays ON during the whole length of the mash process). The grains are added to the mash mixer where they are automatically blended and heated by an electric heating jacket. This heating jacket wraps the outside walls of the mash mixer tun and is turned on/off as necessary by a PID temperature controller to maintain constant temperature within 1 degree Fahrenheit (0.5 °C) or less.

Tools & Materials

(1) 8-gallon (30-L) stainless steel stock pot
(1)12VDC gear motor (from a truck windshield wiper system)
(1) PID Controller model E5CN Omron
(1) Electric heating jacket model WAD561001 from BriskHeat
(2) 3⁄8-inch stainless steel street elbows
(1) 3⁄8-inch x close stainless steel nipple
(1) Stainless steel false bottom
(1) Weldless valve
(1) Aluminum square tube and angle
(1) 14-gauge aluminum sheet metal
(1) On/off switch
(1) Fuse holder with 3-amp fuse
(1) Plastic box
(1) 12VDC Power supply with 6-amp rating

Steps

1. Install the lautering parts

Install drain valve, false bottom and dip tube to allow for lautering in mash mixing vessel.

Drill a 7⁄8-inch hole approximately 1.25 inches (3.1 cm) from the bottom of the stockpot. Install the weldless valve and lay the false bottom inside of the mash tun. Thread the street elbows into the valve inside of the mash tun as shown in picture. Mark the approximate location on false bottom and drill a hole in the false bottom for the male threaded side of the second elbow to go through the false bottom. This will serve as dip tube in the lautering step.

2. Wire the heating jacket

Attach the heating jacket by holding its ends together with the provided spring. Connect the heating jacket to the PID controller. Note that we are using the same wiring diagram for the PID controller as the “Build Your Own Mash Tun’’ article from the January-February 2013 issue of Brew Your Own (https://byostaging.wpenginepowered.com/story2799). The only change is that the controlling load is a heating jacket instead of a pump.

I used a 120-volt 1.1kw heater with a 6 WPSI heating density. In a 5-gallon (19-L) mash, a temperature gain around 0.6 Fahrenheit (0.3 °C)/minute can be expected. If a step mash schedule is being used and the temperature difference in the mash steps is large (more than 10 °F/5.5 °C), the mash volume is more than 5 gallons (19 L), or a short ramp up time is desired, the propane heater at the bottom may be used to assist in temperature ramp. The false bottom and mash mixer prevents the grains from being in contact with the directly heated bottom, thus preventing any scorching of grain). Once the temperature is near 2 °F (1 °C) from set point, the propane burner is turned off and temperature control returns to being a PID controller and heating jacket.

3. Build the stand

Mount the gear motor on the platform. Measure the mash tun height and add at least 3 inches (8 cm) to this dimension and this will be the height of the mash mixer stand. Measure the mash tun diameter and multiply that measurement by 1.5 for the mash mixer extension. The sheet metal is placed on top of this extension and the electric mixer motor is bolted on to it. Weld the structure together (or bring to a machining shop or welder to weld it together).

4. Build the power supply enclosure

The purpose of the power supply enclosure is to make the electrical connections for the on/off switch and fuse (for overload protection). The wiring of this is simple. There will be only two wires to work with. One wire from the DC motor runs in series through the switch and fuse, while the other goes directly to the power supply. Switching the wires from positive to negative or vice versa reverses the motor rotation. The plastic box, on/off switch, fuse holder and 12VDC power supply can be found at specialized electronic supply stores. Do not attempt to perform any electrical wiring if you are not trained. Find an electrician to help you.

5. Build the impeller

The paddle used in this project was built from stainless steel sheet metal and a ¼-inch stainless steel rod for the impeller shaft. At the top of the paddle shaft I welded a square piece of metal to serve as attachment to the motor shaft. I drilled a ¼-inch hole for a bolt to go through it on top and screw into the motor shaft. The blades are angled at approximately 45 degrees overall and each blade was built from a 4-inch x 5-inch (10-cm x 13-cm) stainless sheet metal bent and welded as shown in picture.

6. Screw impeller to the gear motor

Below the gear motor shaft, underneath the sheet metal supporting the gear motor, the bolt used to take the mixers shaft on/off can be seen. Assuming all went well, plug your new mash mixer into a GFCI outlet and give it a test run!