I made pork vindaloo today and after simmering everything for 50 mins the pork is tough. I have had this experience before. I often read recipes that say "simmer for an hour or until pork / beef / lamb is tender." But, I find that the meat is done after 30 mins or less and letting things cook longer just makes them tough. I browned the pork pieces before simmering. Please advise. Thanks.