Charcoal
From Unofficial Stationeers Wiki
10 tomatoes, or any of the other "seeds" gives 100x reagents mix when going through the Recycler.
After that you take your reagents mix, and put it through the Centrifuge, which then gives you 100x biomass.
After that, you put it into your furnace, which then gives you 100 Charcoal - the end product !
1 Charcoal gives you 40 kJ (2 ticks at 20 kW, or 1 second at 40 kJ/second) when used as fuel in the Solid Fuel Generator.