This article may contain one or more independently chosen Amazon affiliate links. See full disclosure.
Alfonso olives are very large, dark purple to purple-brown olives that are grown in South America and primarily Chile, Peru, and Argentina. They have a meaty, soft, and tender texture with a rich-tasting olive flavor that is somewhat bitter and vinegary.
See also: Is Your Olive Oil Fake?
The most popular South American olive variety, this black olive (Olea europaea) was brought to South America by Spanish settlers in the 1500s. They are sometimes called Maddelena olives.
They are brine-cured and packed often in red wine, giving them a striking purple color, or wine vinegar but are sometimes sold packed in olive oil. The Bojita olives of Peru were derived from Alfonso olives.
Kalamata olives can be used as a readily available substitute for Alfonso olives, although they are smaller and softer than Alfonso olives which are somewhat firm in comparison (be aware that textures can vary and Alfonsos can sometimes be softer than expected, even mushy).
Niçoise olives could also be used to replace them although Nicoise are saltier and more bitter than the Kalamata.

What are Alfonso Olives Good For?
Use Alfonso whenever you want an assertive but firm olive that can stand up to a full-bodied wine. In this way, they are a great choice for a charcuterie board.
They are also popular in the classic Peruvian dish, arroz al olivar, or Peruvian olive rice. They are a good choice also for a strong-tasting olive tapenade.