Tempeh starter, also called powered tempeh starter (PTS) or tempeh culture, is a dried mixture of live Rhizopus spores with substrate, which can be soybeans or rice. With most fermented food products you need a starter to push the process in the desired direction. For example, to make good quality yoghurt you need a starter containing the desired lactobacillus and streptococcus bacteria: you can use commercial starters or some yoghurt from your previous batch. In the latter case there is a risk of contamination with other bacteria, a risk which increases with every successive batch. The same principle applies to tempeh fermentation: to produce good quality tempeh you need a tempeh starter with a very high count of desirable Rhizopus molds. Tempeh can be produced by two Rhizopus
strains: Rhizopus oryzae
or Rhizopus oligosporus
, both of which can be isolated from fresh Indonesian tempeh.
Indonesian style tempeh starter
In Indonesia, where tempeh originated and is still produced in small tempeh shops, the tempeh master always uses dried tempeh starter. They make it by placing a handful of cooked and inoculated soybeans between two hibiscus leaves, allowing them to incubate for a few days until the soybeans are covered with black spores and finally drying them in the sun. They use this starter by rubbing the hibiscus leaves above the soybeans to be inoculated. As you can understand, this type of tempeh starter can easily be contaminated with other molds or bacteria. Maybe this type of tempeh starter does not cause health problems in Indonesia where people are more exposed to disease causing bacteria and have developed immunity. However, Indonesian tempeh starter, imported in the USA by Tempeh Online, caused a serious salmonella outbreak in 2012.
Western style tempeh starter
In Western countries, where tempeh production is rather new, tempeh factories always use pure cultures to make sure that the quality of the finished tempeh is consistent and to minimize the risk of failed batches. There are no specific legal standards for tempeh starter, but good quality tempeh starter should contain millions of Rhizopus spores, contain no contaminating, coliform or pathogenic bacteria. Tempeh starter is often extended with sterile rice flower or starch to standardize the spore count.