Ask the Alchemist #134


Would spraying water via a water bottle work or would a small pipe running the length of the roasting drum with small holes in it to spray water be better? Of course, there's the question of how much water and when to add water during the roast. I know this can be used for flavor development and better micro kills at lower temperature; as I have read.

This seems to be a very common misconception. That being that adding water during roasting will give a better micro kill at lower temperature. This seems to be a classic variation of the telephone game, as so many things are. Someone hears something and repeats it slightly changed until it really does not resemble the original facts.

In this case, from the best I can piece together, it comes from a combination of two things. One is that you can have ‘moist’ heat and ‘dry’ heat kill curves and that the ‘moist’ are lower than the dry. The second is the fact that some coffee roasters are equipped with water spray systems. The issue is that to my knowledge these are completely unrelated.

In the first case, it has been taken way out of context. Here is context in full.

Of all the methods available for sterilization, moist heat (steam under pressure ) in the form of saturated steam under pressure is the most widely used and the most dependable. Steam sterilization is nontoxic, inexpensive, rapidly microbicidal, sporicidal, and rapidly heats and penetrates materials”

When you read that I think you will see very quickly that ‘moist’ converted to the lay term of moist or wet when in reality it means steam under pressure when read in context. In short, steam carries a lot of energy. But you have to keep it around, and really, the only practical way to do that is to have a pressurized vessel. None of our roasters are sealed. If you spray steam in, it quickly goes away and has no effect on the microbes. And notice I said steam. If you spray water, you are potentially doing less than nothing as the water, in order to turn into steam, must absorb quite a bit of energy. That energy comes from your beans and your roaster. The result is that if you spray water in, you cool off your roast. In no way does this help microbe kills.

But it does explain why water sprays are in roasters. It is a very effective way to get a very hot roast (one potentially out of control) in cooled down and in control again. Adding steam adds energy to a roast and helps kill things (if you can keep it contained for minutes). Water takes away energy.

As for flavor development, that is news to me. I would postulate that water’s only purpose is to keep the roast profile where you want it. It isn’t like it is going to be absorbed by the beans. At anything over 212 F it is going to flash evaporate thereby cooling the roast, or at least decreasing the rate at which the profile is increasing.

Funny how the telephone game works, and what we think we know, huh?

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