I make 4 and 8 gallon test batches of cheese as a fairly serious hobby. As we all know, standing over a pot stirring for many hours gets pretty tedious after a while. It also gives me a sore back. I've been working on a "Cheese Machine." Basically, it's a store-bought stock pot with removable stirring and heating features. Everything is operated by a laptop computer and custom built controller. My Cheese Machine measures temperature and pH. It turns the heat and stirring mechanism on and off under the control of a "recipe." I write text-based, step by step instructions to control the vat and to signal me when I need to do things like add cultures, or cut the curd. It constantly displays things like: vat temperature, vat pH, heater on or off, stirrer on or off, lists of ingredients, the current step in the "recipe, the time until the next step, and so on. Everything works beyond my expectations. The temperature control is outstanding (within a degree) and I never miss a step; the Cheese Machine alerts me whenever I need to do something. The quality and consistency of my cheeses has taken a very positive turn. I'm particularly pleased with how well the Cheese Machine carries out temperature ramps--something very difficult to do well on the stovetop.
However, there is one feature that still isn't up to snuff. I've been tinkering with the stirring mechanism for a while, hoping to get it working as well as hand stirring. I use a slow turning motor originally designed to turn an auger that moves wood chips into a home wood stove. It's cheap, easily replaced and has enough torque to move through curds. The motor is mounted on a cross bracket that straddles the top of the pot and nestles into the pot's handles. Gravity holds it in place. It never moves during use. For the stirrer itself, I pieced together sections of food grade stainless pipe fittings for the vertical shaft and horizontal arms (tees, crosses, and nipples.) I used standard Teflon tape to seal the joints where the various pieces attach together. If you decide to do this, I'd recommend using the type of threads that increase slightly in diameter as they get farther from the end of the fitting. This insures a very tight fit and makes sure no water gets inside the stirrer. I didn't want to worry about bacteria growing inside the stirrer and eventually contaminating the cheese. I had to custom make a connecting rod to go between the uppermost tee fitting and the motor's drive shaft. This is just a short length of stainless rod into which I cut threads matching the stainless fitting on one end. Finally, there is a coupler that attaches the unthreaded end of the connecting rod to the shaft of the motor. The coupler tightens with several hex screws. Eventually, I'd like to replace this coupler with a magnetic coupler that allows the stirrer to stop turning if something solid (like a stirring spoon) accidentally falls in the vat. It would also allow the stirrer to be easily and quickly removed from the stirring assembly without needing to use tools. I typically remove the stirrer from the motor assembly and put it in the dishwasher to clean.
The stirrer does a great job stirring the milk before the rennet is added. Wherever I measure the temperature anywhere in the vat, the milk is at pretty much the same temperature, whether I'm on a step where the temp is held constant or on a step where I'm slowly ramping the temperature over time. This alone has made my efforts worthwhile since these steps can go on for over an hour.
However, the stirrer doesn't really stir the cut curds as well as I'd like. I still have to use a spoon to help out. I was hoping the multiple sets of cross arms would provide sufficient agitation to keep the curds moving around the whey and also keep them from knitting together. However, this doesn't happen with the current design. The bottom-most arm either shoves the curd mass in front of it, or the curd mass slips between the two lowest arms. Either way the curds continue to knit together into a larger and larger mass. My first tweak was to soldered sweeping blades (sort of like a fan blade) to the bottom most set of arms. The blades are soldered across the top of the arm all the way from the central shaft to the tip of the arm. They are positioned facing forward and angled downward so they almost touch the bottom of the pot. This had helped a little--it gets the curds off the bottom of the pot. But it still doesn't do the job right. Part of the problem is due to the nature of curds. They start out very fragile. They need a gentle touch in the first few minutes. But as they lose whey and begin to firm they can stand a more vigorous stirring. I have not found a shaft turning rate that is both gentle enough for newly cut curds, and vigorous enough to keep the curds continually separated. Part of the problem is simply the way the curds are being agitated. They are heavier than whey, so tend to quickly fall to the bottom of the pot. They need to be lifted off the bottom and kept moving without being so bullied that they disintegrate.
At this point, I'm considering various tweaks. One is to attach blades to all the arms. I'm hoping that a curd swept off the bottom of the pot by the lowest arm will then be gently lifted higher and higher buy the arms above. This could mimic the way a spoon stirs curds from the bottom of the pot toward the surface. Another idea is to use a variable speed stirring motor that can treat freshly cut curds gently, but then pick up more and more speed as the curds firm.
Any ideas would be appreciated. The Cheese Machine will never be like a bread machine or ice cream machine. It will never be something you load up with ingredients, turn on, and walk away. It will always require human intervention to carry out certain steps. But, if the milk heating steps and the curd stirring steps can be automated, it would make cheese making a lot less tedious. It would also enhance the ability replicate cheeses from one batch to the next.