Puget Sound Mycological Society had recommended the technique. I had made similar experiments with porcini buttons years earlier. For whatever reason, wrapping the matsi buttons in foil was a required step. It seemed to me the best way to defrost them would be directly in the soup broth. I unwrapped the foil to find, luckily, that I had carefully cleaned the buttons and trimmed the stems before freezing. They looked a little darker but otherwise in good condition. I could smell the signature "autumn aroma" even in their cryogenic state.
My experiments are not over. I still need to test the vacuum-sealed pair of buttons, and next time I'll try not to lose them in the freezer for more than a few months. Overall, I'd say the results are encouraging for matsutake fans who want to experience the mushroom's unique taste year-round.