Keep in mind that the size of the container, the amount of water in the container and the surface area (or better yet the amount of contact area the bottom of the container has with the heat source) will determine when the water is adequately “mixed” to reach killing temperatures for pathogenic organisms and parasites. That is why many references say a “rolling boil”/large bubbles, indicating there is sufficient mixing of the water to reach killing temperatures in all parts of the container. A very deep pot/cup with only small bubbles may have water at the surface, which has not reached high enough temperatures to kill certain organisms.

Recognizing that most pathogenic bacteria are likely killed when the water reaches a rolling boil, most steam autoclaves (steam under pressure is far more efficient at killing, then boiling) operate at 250 F (well above 212F) under 15psi and the minimum autoclaving time is 15 minutes (although this is in part to allow steam to access all parts of the chamber).

I can tell you from personal experience, we use chemical (and biological indicators) integrator strips, which start to measure a given/standard heat (250F) over time. The use of chemical change tape (you may see these on surgical supply packs or other medical devices and supplies), which changes as soon as the given/standard temperature (250F) is not a valid indicator of sterilization. I have run studies in which autoclaving (at 250F under 15psi) for up to 10 minutes was insufficient to kill indicator bacteria (spore forming rods – a heat resistant Bacillus species), despite the change of the indicator tape.

Also keep in mind there is both heat labile (easily destroyed by heat) and heat stabile (resistant to heat inactivation or denaturing) bacterial/fungal toxins (proteins). When one is heating food/water, one is not only attempting to kill the living organisms, but also the toxins (both exo and endo) produced by the bacteria, both living and dead). It is possible the references to boiling water longer then either a rolling boil or for 1 minute are taking the presence and heat resistance of any bacterial toxins that might be present. While I have never heard of bacterial toxin poising from water (food – definitely yes), I guess it could be possible if there were a lot of organic material supporting bacterial growth.

Although, it is interesting that UV water purification devices such as the Steri-pen do not address or take into account any residual bacterial toxins. The MIOX solution might have some inactivation effect on toxins (I really do not know), but certainly filters with charcoal beds and boiling should be considered for water where the possibility of residual bacterial toxins could be present.


Pete