Stale water – is it an issue?
One of the topics that comes up from time to time in coffee discussions is if stale water is an issue. One of the arguments, for example, for using a Heat Exchanger instead of a double boiler is that if you are using it at home and the espresso tank is fairly large then the water sits in there for a long time. The reason is that the water for espresso is not used even for steam and double boilers are so efficient with water that there is not much necessary flushing to waste water. This means that since espresso itself does not use much water and flushing does not use much water, if you do not make many shots you will have the same water in the boiler for a long time. As it sits there some fear it may go stale. One solution would be to have a smaller boiler, but this may result in less temperature stability. Another solution would, of course, be to intentionally just waste water, but this also seems silly.
I do not know if water does go stale or not, but it does not strike me as likely. Water can sit in a water bottle for years without problems, and my guess is that this would be true even if there were more air available in the water bottle (although if it were kept at room temperature and was not air tight I am not sure if it would remain safe for years.
There is an obvious experiment to test this, and that is to leave water in the boiler for a few weeks or months and taste it compared to fresh water. There is only one problem with this solution – it would require not using the machine for months and I can’t go without espresso that long (and, of course, there is the issue that I do not own a dual boiler).
Alas I have more questions than answers on this post.