In my opinion, bran alone wasn't enough to heat up the sawdust. I could've not added enough bran but for me adding more flour did the trick. I know a lot of people add soybean powder, chitosan, milk powder, etc.. to make their flake soil more nutritious. It's obvious why people would keep their recipe a "secret" because they put countless of hours into making flake soil that work and produce good results. However I'd say that most guides out there is good enough imo for the average hobbyist. Making flake soil is really just experimenting what works for you.