I opened one of those old tane koji packages I found recently. It’s about 30 years old but maybe still viable.

It grew slowly, if at all.

After the normal 48 hours:

So I let it grow another 12 hours

It turned out quite good, however slow and weak.

The problem is, I was not very scientific. Everything else was the same, including the uncleaned trays, which could very well have inoculated the barley from spores left from earlier batches. I’ll try again later with well cleaned trays. In the meantime I’ll stick to new bought tane koji.