http://durgan.org/2017/April%2... 30 April 2017 Tempeh: Removing soy bean skins
Soy beans skins need be removed for making tempeh, since the starter spores have difficulty penetrating the soy beans with shell (skins) in place. The skins are firmly in place and must be loosened before they can be removed using agitation.

Process is to: wash the beans, soak in cold water for 12 hours, agitate the beans by rubbing between hands, rinse the water carefully to separate the beans from the skins which partially float. Depending upon the time expended most of the skins will be removed. It is desirable that the beans spit but this is not essential. Soaking increases the volume by doubling.This is the first operation for making Tempeh.