Bitter, or Seville oranges are too sour and bitter to eat as a fruit. But they’re important ingredients in many foods. Traditional marmalade is made with these oranges, as is orange blossom water. The rind has a cleaner, more intense aroma than sweet oranges, so it’s traditionally been used for liqueurs, such as Grand Marnier and Triple Sec; as well as for sweets. You can substitute regular orange rind, but use the Seville zest when you can. In Iran and southern Mexico, they use fresh bitter orange juice in the same way as you would use lemon or lime juice.