The aesthetics of limescale
Anyone who lives in a place like Berlin, where water is hard, and who uses a kettle to boil water, will have seen the effects of lime-scaling. In fact, in some areas around the world you only have to turn on your water tap and, unless you immediately clean the sink after use, the limescale deposits start forming—sometimes even visible to the eye!
The reason for this is “water hardness”, which refers to the amount of dissolved calcium and magnesium in the water. Hard water is high in mineral content, formed when water percolates through deposits of limestone and chalk which are largely made up of calcium and magnesium carbonates.
The good news is that water hardness is mainly an aesthetic problem. While water with limescale deposits may not taste great, it’s fortunately not harmful for your body. In fact, magnesium and calcium are things our bodies need!
Either way, we wanted to solve the limescale problem with our machine. There is the taste argument, but also purely technical reasons: if limescale becomes too thick, we lose heat in our vaporization process, meaning that we have to use more energy to get the same results (which then in turn may translate into higher carbon emissions through the public energy system). Also, there is a maximum of how much limescale our vaporization unit can tolerate, before there is simply not enough room for water to boil.
Our first attempt at solving the issue was Teflon coating, which is said to reduce the rate of scale formation tenfold! Teflon can prevent minerals from bonding with surfaces and makes it easier to remove deposits in case they do manage to stick. However, in our experiments we found that Teflon coating wears off over time. And then, even more worrying, there’s sometimes so much lime-scaling that cleaning the machine would be a near constant job! We hence concluded that Teflon (alone) is not the right solution for Mitte.
Next, we looked into water filtering. The rationale is that if we manage to remove unwanted minerals before they are introduced to the vaporization unit, there are no sediments to form. First results are promising, however, the sodium which is introduced during the filtration process gets into the aerosols and then settles down leaving an equally displeasing white layer above the water level. So, the taste issue is dealt with, but the aesthetics are still suboptimal.
Finally, we realized that we can effectively halt the process of lime-scaling by regularly replacing the water in the vapour distillation heating cell. The “old” water contains high levels of dissolved minerals, however, if we flush it out before they manage to attach themselves to the surface, the process of sedimentation is unlikely to play a significant role over the lifetime of the machine.
While we seem to have arrived at a satisfactory solution, we constantly strive to improve, so we’re currently also testing to use magnesium instead of sodium during the filtration process, which could reduce the intervals at which we need to replace the water. Whether that proves practical or not, do expect to see more developments on this going forward… just like on pretty much any aspect of the machine. As Steve Jobs was saying, “there is always ‘one more thing’ to learn!”