All miso paste is made by fermenting soy beans, and sometimes barley and/or rice, with koji (an edible fungus that grows on rice and is also known as 'rice malt' or 'rice mould'). Red miso is made from a higher percentage of soy beans and is fermented for a comparatively long time (over a year in most cases) to create a deeper, more savoury flavour. If you are looking to explore the wide world of miso, japancentre.com's Miso section is a good place to start.