This is due to Blackcurrant acting as a MAOI. The MAOI activity is not much to speak of compared to the Harmala-alkaloids, but it still have a definitive effect if taken in the right dosages. Blackcurrant has been demonstrated to inhibit MAO-A 37 % and MAO-B 60 % in vitro, and 70 % to 90 % MAO-B inhibition was found in three human subjects [Merz & Co GMBH, 1991]. The same study concludes that maximum inhibition is obtained 60 minutes after application, and that 20 grams Blackcurrant is the optimum dosage.

The MAO-A inhibiting is what you want, as that is the enzymes that break down tryptamines. MAO-B inhibiting is certainly not needed, and can potentially give unwanted interactions. Blackcurrant mainly acts as inhibitors for MAO-B. Thus, Harmala-alkaloids is a much better option, as they are selective MAO-A-inhibitors.

Acidic environments will dephosphorylate Psilocybin, i.e convert it into Psilocin. This will give a stronger effect for a shorter duration of time, as the body will not need to do the time consuming conversion. I often make mushroom tea with a good dose of lemon juice, that works well. Anything that make the tea acidic will do the trick, including orange juice and vinegar.

Wow, interesting! This would be very important knowledge if it turns out to be correct. I would love to hear more about this, if anyone has any information.

As for the Grapefruit theory, this is indeed interesting stuff! Thank you for bringing that to the community's attention. I look forward to see how this thread turns out.