The kind of flour you use is up to you. I use British white, rye, spelt wholemeal, heritage grain, chocolate (using 20% cocoa powder) and beetroot (using pureed beetroot instead of water). I recommend three things though. Firstly that the flour you use is organic, secondly that it is freshly milled, and lastly that it is stoneground. This will give your microbes the best nutritional support and it adds extra microbes via the flour, which also supports the health of the ferment.