You made char by the double chamber, cone pit, kiln or any other technique. The following step in biochar making is grinding char into smaller sizes. Frankly, I don't bother to do that for smaller than fist-size pieces. Many do though. Many low-cost options come to mind, passing through wood chippers, putting into bags and driving back and forth over the bags and so on. Here is a DIY project to build a machine to grind char into smaller sizes. If I know Tim a bit, he will be perfecting his invention, and this will turn into a series. Also, the "Way Out West Blow-in blog" is a must-follow youtube channel in my opinion. So please do check their other videoes.
I simply love the way the fellow kept improving the design until he got it to a working state. His narration was very enjoyable to listen to without getting frustrated at having to do it over again (in fact, I think he enjoyed having an excuse to use his plasma cutter again!)
Unless your going to be processing a whole lot of charcoal, there's a whole lot of work to build one (as he states) but it was sure fun to watch! A real tinkerer at heart.... 💓