The idea of using beeswax to measure water pasteurization temperature is too good of a possibility to give up on even though it has been mentioned for years. One thing that has made the recent solar cooker models successful was that the materials were available around the world (at least in the cities). This has made it often easy to just ship around the information on how to build a cooker without having to ship the cookers themselves. If we could only come up with a thermometer that was just as easy, we would have a winner.
It is reported in chemistry manuals that beeswax melts at a relatively low 62º C. Bees are found on every continent and given the different conditions in each location, the exact melting temperature may be somewhat variable. It is possible that this temperature can be used to measure whether water water has been heated to a high enough temperature to make it safe to drink. There was some discussion of this in an interview with microbioligist Dr. Bob Metcalf here:
Tom Sponheim: I know that bees wax melts at about 62° C. Would you think that would be a safe indicator at this point?
Robert Metcalf: It would. I have tried beeswax. I don’t have my data right here but sometimes I have found it variable … the temperatures. And, if anything, I think on the safe side, it melts higher than that. Waxes have stated temperatures at which they melt at, but they actually start changing phase in a range of temperatures. I am really looking for a good wax that melts at around 62° to 63° C. That would be really good … about 145° F.
TS: So you don’t think that, at this point, bees wax is safe enough to rely on?
RM: I have run those tests with beeswax and I don’t have the data with me…
TS: Maybe we can talk about that at another time. Because it would be nice if there were some wax that occurred everywhere in the world that could easily be gotten to by people and they could make their own thermometers.
RM: That is correct. And when I have actually run those experiments, I have put beeswax into WAPIs, made the water pasteurization indicators and put those in there. As I recall, the temperature is much higher than 62° C that it melts at.
TS: I see.
RM: And so, when waxes are given temperatures (in the literature) you really have to try it out and see if it is going to be melting at that temperature. But I agree that that is something that needs some further work … the beeswax.
We have also found that mixing a small amount of carnauba wax with the beeswax (~1:5 ratio) raises the melting temperature of the beeswax to 70º - 75º C. Carnauba wax is a product of Brazil and can be bought in the US at woodworking supply stores. Initial testing has shown that the melting point of this carnauba/beeswax mixture remains the same after repeated re-melting (up to ten times tested).