Annatto, also known as achiote, is a spice known more for its colour than its flavour. The seeds of the annatto tree are dried into hard reddish-brown pellets which are used as a natural dye (including for lipstick, hence it's also called "the lipstick tree") and food colouring. The shades range from golden yellow to deep red, depending on the concentration.
It's sometimes used as a much cheaper substitute for saffron - purely for its colour because the two spices taste nothing alike.
The flavour of the seed is subtle. If you chew on one not only will you stain your tongue red, you will also taste a light peppery, minty flavour. Often, though, the seeds are mixed with other spices, so the subtle flavours are obliterated.
For Caribbean yellow rice, fry some annatto seeds in oil, until the oil takes on a deep orange colour. Strain out the seeds, then use the oil to sauté chopped onion, garlic and bell peppers until the vegetables start to soften. Add long-grained white rice and stir, to coat with the oil. Add water and stir, then cover the pan with the lid and cook until the rice is done.
To make a spice rub for beef, grind lightly toasted annatto seeds and cumin seeds with black peppercorns and chilli until the ingredients form a powder. Mix the powder with garlic and shallots that have been pounded in a mortar, then stir in some salt, dried oregano and fresh lime juice until the ingredients form a paste.
Massage this mixture onto steaks and refrigerate for a few hours. Remove the meat from the fridge about an hour before you want to cook it. Sear the steaks quickly in a hot skillet (or on a barbecue) until medium-rare, then slice and wrap in hot corn tortillas. Serve with fresh lime wedges.