I am originally from England so a coffee cake to me actually has coffee IN it ! (Even after nearly 35 years here in Canada I still look at recipes for coffee cake expecting coffee to be one of the ingredients. Our favourite recipe  for a coffee cake or cupcakes : 

                                    1 2/3 cups AP flour

                                    1 cup sugar

                                     1 tsp baking soda

                                     2 tsp instant coffee in 2 tsp boiling water

                                      1 cup low fat buttermilk

                                       1/2 cup melted margarine

                                      1 1/2 tsp vanilla extract

Combine ingredients, pour into 9 by 9 pan or 12 cupcake pan. Bake at 375 degrees for 20 minutes. Sometimes these are iced with coffee icing but I have recently discovered KA's cappuccino chips so add 1/2 cup of these to the batter instead of icing the finished cakes. Now...here is my puzzle, within a few hours or certainly by the next day they have turned green - really green! I thought maybe the buttermilk was reacting with the baking soda so made the recipe with ordinary milk - they still turned green! They even turn green in the freezer!   I hasten to add that they still taste really yummy!  Can anyone tell me why this is happening ?

Thank you - Merlie