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I am confused with respect to why the source of the heat to boil the water matters. An electric kettle kills more pathogens than a kettle on a gas stove? Why? And what about an electric stove or a hot plate? I thought it was the boiling that killed the pathogens so why does it matter what type of heat brings it to a boil? Hopefully Dr Fallingham will answer this on the webinaire.

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Replies to "I am confused with respect to why the source of the heat to boil the water..."


In page 5 of the article Reducing Exposure to Nontuberculous Mycobacteria (NTM), Dr. Falkinham stated: First, if you are worried about swallowing NTM, boil water for 10 min. That will kill NTM. This list of recommendations has been updated May 3, 2021, because of a publication comparing the ability of killing fecal bacteria (Escherichia coli) by boiling water in a pan versus boiling water in an electric kettle. The electric kettle was far superior in its ability to kill the bacteria, so I recommend purchasing an electric kettle to boil water. They are available at the big box stores and online.

The publication that he refers to is attached. As you can see, it shows the results of a comprehensive evaluation of household water treatment in rural China, in which they measured many things, including the difference in efficacy in reducing thermotolerant coliforms between boiling water with electric kettles or pots. In page 3 of the document, I highlighted the procedure followed to measure the temperatures reached with both heating methods. In the highlighted text, you will find references to Figure S1 and Figure S2, which I am attaching as Slide 1 and Slide 2.
In Slide 1 you can see an example of the electric kettles and pots used, as well as the location of the sensors, and in Slide 2 you can see the variation in the temperature recorded each minute by the sensors during a period of 72 h. Each peak corresponds to a “boiling” event. Clearly, the temperatures reached with the kettle were more uniform and higher than with the pot, which can explain the higher efficacy of kettles in reducing coliforms. The higher uniformity and temperatures attained with the kettle are to be expected just because of the automatic way that they operate at. On the other hand, the pots were heated with firewood, so I can easily envision that people had to get firewood, feed the fire, put water in the pot, and wait for it to boil, all frequently resulting in “heating” more than “boiling”.

Now, I find it difficult to extrapolate from the conditions in rural China to the conditions of most of us. Maybe while camping one could use firewood to boil water in a pot, but otherwise I would guess that few of us would do it. Therefore, I doubt that under our normal conditions the electric kettle would be “far superior” than a pan to boil water.

But, how about the 10-min requirement? In my exchange with Dr. Falkinham, he clearly stated that reaching the rolling boiling stage suffices, which is when the electric kettles automatically shut off. So, I think that he assumes that the water in the kettle is exposed to temperatures around boiling for at least 10 min during the whole process. It is not clear to me, though, that such an assumption can be supported by the graphs in Slide 2. The temperature in the electric kettle reaches a very sharp peak and descends immediately. (By the way, the temperatures never reach 100C because the sensor was attached outside the kettle.)


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Boiling Water Electric Kettles EHP (Boiling-Water-Electric-Kettles-EHP.pdf)