Red Velvet Cupcakes end up as liquid pink evil

[BeccaJaneStClair]

I remember the first time I ever heard of a red velvet cake....and the person who baked it said it called for a WHOLE BOTTLE of red food coloring! 

Mostly I just liked the cream cheese icing. Yum!

Yep. Our recipe calls for a whole bottle, too.  THEN, we usually dye the icing - At christmas, it's green, and at valentine's day, pink. 

IF anyone's interested, here's the "family recipe" we use:

Red Velvet Cake
From the Kitchen of: Jane Sweitzer
Ingredients
 
1 1/2 Cup Sugar    2 Eggs    1 Tsp. Salt    1 Tsp. Baking Soda
1/2 Cup Shortening    1 Tsp. Vanilla    1-2 Tbs. Cocoa    1 Tbs. Vinegar
2 oz. Red Food Colouring    2 Cups Flour    1 Cup Buttermilk    
Instructions
Cream sugar and shortening until fluffy. Add colouring, eggs, and vanilla. Beat until snooth. Sift flour, salt, and cocoa - 2 times. Add alternately with buttermilk. beat until smooth, combine soda and vinegar, blend gently into batter. Bake at 350º F for 30-35 minutes.

Frosting For Red Velvet Cake

Ingredients
1/4 Cup Flour
1 Cup Milk
1 Cup Shortening
1 Cup Sugar
1 Tsp. Vanilla
1-2 Drops Almond Flavouring
Instructions
Combine flour and milk. Cook until thick. Cool. Cream sugar and shortening. Add Flavouring. Add Sugar to cooled mixture. Beat until fluffy enough to spread.

[MirthFairy]

As to the other vinegar called for in the recipe, my grandmother's recipe note tells me to "Reserve baking soda and vinegar until all other ingredients have been mixed.  Make a small hole in the batter on one side of the bowl, add baking soda, make a small hole on the other side, add vinegar, mix well." (I honestly don't know WHY you're supposed to do this)

I'm not certain why you would want to reserve the baking soda, but the reason why you would reserve the vinegar is so I won't prematurely react with the baking soda. If you put it in to early and stir the batter, the delicate bubbles caused by the soda-vinegar reaction will pop and your cake won't be as fluffy. You also won't want to mix this sort of cake in a metal bowl. The acid in the vinegar will react with the metal causing a nasty metallic taste.

For fun, just pour some baking soda into a bowl with some vinegar and watch it foam. I sometimes use this reaction to clean my drains (1/2 c baking soda down the drain, add 1 c of vinegar, plug drain and leave for 10 minutes. Chase with 5 cups hot water.)

FYI - Baking soda requires an acid to react, baking powder is soda with an acid already added, so all you need is a liquid. Cream of tartar is an acid, so sometimes it'll be added to baking soda only recipe that has no other added acid.

See also Wikipedia:
Cream of Tartar
Baking Soda
Baking Powder

[Muria]

Chemically, milk plus vinegar is a decent substitute for buttermilk, but the real thing almost always produces superior results for me.  I've used half  plain yogurt/half milk a few times when I've been out of buttermilk, but it still doesn't come out quite the same (though better than my experiences with the milk/vinegar combination, as it doesn't thicken enough). 

Another good substitute for cake flour (if it's carried locally) is White Lily all purpose flour.  They use exclusively soft wheat in the flour, which produces a much lighter product (soft wheat has less gluten, which is good for yeast bread, but weighs down quick breads, cakes, and biscuits). 

I have a great book called "This for That: a Treasury of Savvy Substitutions" that tells you good substitutes when you don't have the required recipe item (including the milk/vinegar substitute, and the self-rising flour information).  The best way to fix what you had would have been to taste the batter, realize the problem, and add in extra ingredients to account for the extra leavening.  Once it's baked, I'm not sure there's anything you can do about it.