There are two ways of cracking olives, the fast way and the slow way.
The slow way is time well spent, especially when done outside on a warm autumn day. And if you have an olive cracking assistant it is the most pleasant of jobs.
The olives need to be smashed just so, any harder sends the pit flying and the reason why my older boys were not allowed to help. Now my favorite kitchen gadget is a beautiful piece of golden calcite which is indispensible during olive season or whenever I am cooking one of Paula Wolfert’s Moroccan recipes. In fact, she suggested this method to me and it worked so well I thought it was genius.
Alternatively, a fistful of olives can be placed in a plastic bag and wacked with a wide, flat hammer, the kind used to tenderize steaks or flatten chicken breasts. I have never tried this method yet.
The fast way uses a special machine, such as the one at the Jerusalem Bazaar, where the olives are poured in from one end and rumble out the other, all perfectly cracked. This might save a lot of time but it isn’t nearly as fun.
Why do the olives need to be cracked in the first place?
All olives, especially green ones, contain oleuropein, an extremely bitter water soluble compound. Cracking or slitting olives facilitates its removal by creating more surface area for it to escape. One method is to soak the olives in water for 7-10 days so the oleuropein dissolves into it. Although not poisonous, anyone who has eaten olives right off the tree knows that olives are inedible if not properly treated. When using the lye method to cure olives, slitting or cracking is not necessary.
Other interesting posts on olive curing techniques
Curing olives using the water method and varieties common in Israel