In a food processor or blender, combine garbanzo beans, black beans, olive oil, garlic, tahini, and lemon juice. With the motor running, drizzle in water until the beans are blended and a smooth consistency is achieved. Add the cayenne, cumin, salt, and black pepper, then blend again. Taste and adjust seasonings as desired. Makes 4 cups. keep covered and refrigerated until served, up to five days. Serve with bread, pitas, or chips.