One of the first questions people always ask us is ‘what is superheated steam?’ Well, superheated steam is simply steam (or water vapor) that has a temperature higher than the saturation temperature at a particular pressure. If you do not like anything too technical, saturation temperature is more or less boiling point. So, at atmospheric pressure where water boils roughly at 100 oC, superheated steam is water vapor at a temperature higher than 100 oC.
Now that superheated steam is simply water, how can it be used for roasting? Well, superheated steam is steam that is hungry for water; it needs water to become saturated (and happy J). This is why it can be used for dry heating – just like heated air. One very nice thing about superheated steam roasting is that this steam would blow away all (or almost all) the air in the roaster, filling the roasting chamber only with itself. With hardly no air, oxygen left in the roaster would be negligible. And if you know that oxygen causes many undesirable reactions in coffee beans, you can easily guess why not having oxygen is a good thing!
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