Years ago I lived in China and loved sichuan food and those delicious sichuan peppercorns. However I have never been able to get that numbing bubbly flavor out of the ones I have bought in supermarkets. Any idea why that is? Do you have to specially prepare them before adding to a dish to get the desired effect? I typically just crush them up a bit and throw them in? Am I doing it wrong or are the ones sold here not fresh enough or something?