My espresso biomaterial was put to the test and baked in 500 F. It hardened however, as you can see below, the connecting tubes are not sealed as they were before baking.
Does it work as a bioreactor? It does. However because the structure isn’t as air tight as I’d like a bioreactor to be, I do not think it is wise to use as a building material for it.
Earth Organization for Sustainability: Cascadia 