To prepare the yucca, put the yucca in a piece of doubled-up cheesecloth and squeeze to strain out the excess liquid. Transfer to a large bowl, cover, and refrigerate for several hours. Strain the yucca again to extract excess liquid. Season with the sofrito or achiote paste, and pepper, and mix to blend the flavors.
Meanwhile, make the shrimp filling. Heat the oil in a large sauté pan over medium-high heat. Add the onion, season with half the salt, and sauté for about 5 minutes, until the onion begins to soften. Toss in the garlic and peppers, and sauté for about 5 minutes to soften. Add the sofrito, oregano, cumin, black pepper, cayenne, achiote paste, and the remaining salt, and stir to combine. Add the shrimp and cook until it is translucent, 4 to 5 minutes. Remove pan from the heat and set aside to cool.
When you’re ready to fry the alcapurrias, heat 3 to 4 inches of oil in a large saucepan over medium heat until the oil reaches 350°F. Strain the yucca mixture through a double layer of cheesecloth again, extracting as much liquid as possible. Prepare a bed of paper towels for draining.
Put the flour into a shallow bowl. Scoop ¼ cup of the yucca mixture and form it into a patty in your palms. Put about 2 teaspoons of the shrimp filling in the center and close the patty to make a tiny football shape. Coat the ball in the flour. Repeat until you have used all of the yucca or filling. Slide the alcapurrias into the hot oil and deep-fry until they are golden brown and cooked through, 6 to 8 minutes.