Despite their name and appearance, Szechuan peppercorns are not related to true peppercorn. The tingling sensation they leave is also not from capsaicin, which creates heat in chili peppers. It comes from a substance called sanshool, which is naturally occurring in these “peppercorns,” actually the berries of the prickly ash tree. As these berries are dried, they open up in a flower shape that give it its nickname of hua jiao, or “flower pepper.” The seeds are discarded, and the husk is what is used.
 
Before the introduction of the hot pepper to China in the 17th century, ginger and Szechuan peppercorn were the primary sources of heat in Chinese cooking, and had broad culinary and medicinal uses.  The “mala” flavor profile, numbing and spicy, relies on Szechuan peppercorn.
Because these are handmade with natural materials, variations should be expected.