I'll admit this is a totally unexplored area but my chemical engineering background told me to try it out.
My own empirical experience so far is that you have to have a very big surface area of the sink to get a reasonable influence over the relative humidity in the space. I don't have enough data to prove anything single variably yet, but I get the feeling that the KCl sinks are just attenuating the natural humidity swings.
For example, I noticed 4-5 weeks ago that I was starting to lose a bit of mass in the weekly weigh ins and that a small tiny crack was starting to appear at one end on the crust. Humidity was a steady 85%.
I wasn't ready to pierce just then so I immediately added a hard surface to the cheese cloth wall. I leaned the large lid of the container against the cheese cloth wall so that I was reducing the air flow rate by at least 95% (I left the base away so some air movement could still take place). Humidity went up and stayed at a nice stable 90%+ and no more cracks. Logically, the kCl sinks should have started fighting this but they are clearly too small to win.
I've noticed that when I had the environment at 85%, I had to replenish them with water to keep a slushy saturated mixture, but now they are swimming in excess water (so essentially no longer sinks).
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Side note:
Alongside this Stichelton I made a big Cambozola wheel and tried a similar technique with it but slightly different. I made it a mini cave out of acrylic sheet glued together in a box and then laser cut large holes in the base and ceiling of the box (none of which you can see in the picture!). I then on a daily basis used pieces of plastic to cover or expose these holes and managed to maintain a pretty constant 95% humidity just from the cheese itself.
However, what I found was that the box started to act like a chimney and so there was a steady but small constant flushing of air but at high humidity. It really liked this and the PC grew like crazy.
My next project would be to combine the two mechanisms into a larger box and use a kCL sink with a very large surface area immediately below the base. Then I would use the natural convection to slowly pull air in over the sink before it goes into the cave area above through the holes and then out the top.
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The big thing for me is that the cheese itself is very happy. Really slow stable growth of the crust moulds. Nothing running away but everything growing nicely. Nothing bad looking on the outside, no blue run away, all interesting whites, browns and maybe a hint of pinks. Smells very nice and mellow. I think I've just been very lucky to find the right conditions for this particular cheese.
I'm supposedly 4 more weeks till I'm opening it up but I'm starting to climb the walls. I think I'm going to give up at Easter.