I was reading about a process implemented by Bühler (a maker of coffee and cocoa processing machines) that applies dry steam of water for 25sec under 5.5 bar pressure directly before drying and roasting the beans. They say this reduces the infection from 100 Million anaerobe mesophile per gram to less than 100.

Now I wonder if it makes sense (despite your “no”) in my home setup to take the strong and dry steam of my commercial grade espresso machine (a vintage model with a 5 liter boiler) and blow it over the beans for half a minute immediate before roasting them? Could that have a positive effect?

The pressure in my machine is about 1.1bar, but a lot of this pressure is lost while spraying at the beans. I just thought that the high temperature could be of any use ( boiling or at least boiling temperature at the moment hitting the beans).

Unsurprisingly my answer is still 'no'. And the why is because your home steaming would not be under 5.5 bar pressure. That is critical to the kill rate. Without that, it serves no purpose at all.

As for the steaming option, and the link to that page, I will point out the first thing I saw:

"Basically, a debacterization is not absolutely necessary. The normal roasting process is quite sufficient for the number of bacteria sufficiently reduce and to comply with legal requirements."

I’ll grant that 212 F can burn you, but there just isn’t a lot of total energy there spraying out of your steam wand. And it is completely uncontained. It’s just blowing past the beans. And the top of them at that. There is too much hidden space that isn’t seeing even that temperature. That is another reason that the beans are pressurized. It contains all that energy.

For your machine, that is 1.1 bar total. Atmospheric pressure by definition is 1 bar. Totally disregarding (for the moment) that it drops instantly to 1 bar as you steam, and loses a lot of heat, it at a 10% increase as opposed to what they use: 530%. To put it in perspective (in a loose allegorical way), say it takes 530 lbs of crushing force to kill you. But someone puts 10 lbs on you. Are you going to die? Or even be hurt? Even if it is put on your for a hour? Or a day? See what I am getting at?

That said, they do make a nice point that the introduction of moisture to the whole beans will facilitate a nicer separation in some beans of the husk from the nib. But again, it takes pressure or time to inject that moisture. Just hitting the beans with atmospheric steam is not going to penetrate very well.

I am not trying to be a nay-sayer. I just would hate to have you waste time for no purpose or reason.

Just roast the beans well, starting with a good high temperature (350-400 F), and your bacteria counts will be just fine.