Combine goat, beer, orange juice, lime juice, garlic, cumin, and salt. Cover and refrigerate for at least 1 hour or overnight.
Drain the goat, reserving the marinade, and pat the meat dry.
Build the Stew:
Blend onion, tomatoes, bell pepper, cilantro, and achiote until smooth.
Heat oil in a Dutch oven. Brown the goat in batches, then return all the meat to the pot and add the blended mixture. Cook for 8 minutes, stirring occasionally.
Braise:
Add reserved marinade, stock, salt, and pepper. Bring to a simmer, cover, and cook gently for 1 1/2 to 2 hours until the goat is tender.
Uncover for the final 20 minutes and reduce the sauce until glossy. Adjust citrus and salt before serving.
Notes
Bone-in goat shoulder gives the sauce body; boneless goat will cook slightly faster.
For alcohol-free cooking, replace beer with additional stock and 1 teaspoon malt vinegar.