Preheat oven to 400 degrees Fahrenheit. Line two muffin tins with 24 cupcake liners or grease tin wells.
In a large mixing bowl or mixer, combine flour, sugar, baking powder, salt and cocoa powder in a separate bowl.
Add oil, mayonnaise, buttermilk, beet juice, and eggs to dry ingredients. Mix on medium speed or by hand for about 2 minutes, scraping sides and bottom at least once while mixing.
Fill cupcake liners about 3/4 full, leaving some room at the top for expansion. Bake in the oven at 400 degrees Fahrenheit for 5 minutes. Turn oven down to 350 degrees Fahrenheit and bake about 10 minutes more. Cupcakes are done when inserted toothpick comes clean from the middle or when the top of the muffin springs back when pushed.
Make frosting. Mix shortening for about 2 minutes until creamy. Add sifted powdered sugar one cup at a time, when mixture gets very thick, add milk and then the rest of the powdered sugar. Scrape the bowl sides and bottom, add salt and vanilla.
When cupcakes are completely cool, frost cupcakes. Enjoy!