Hi all,
Recently I made some muffins that turned out like cookies (I am new to cooking). I'm not sure exactly what the problem was, but it may have been b/c I forget to mix the dry ingredients before I put the milk and butter in. Anyway.. as I was thinking about what may have gone wrong, I took a look at my baking powder (I used Rumford baking powder) and saw that it has three ingredients:
1) Calcium Acid Phosphate (acid)
2) Bicarbonate of Soda (base)
3) Cornstarch (filler)

After doing some research I figured out the following. Calcium Acid Phosphate (aka Calcium dihydrogen phosphate) is a fast reacting acid that occurs at room temperature. I also read that some baking sodas are referred to as "Double Acting" b/c they have one acid that will react quickly at room temperature and one that reacts at high temperature. This Rumford baking powder sounds like it is single acting b/c it only has the one acid, but on the can it says "Double Acting". I am confused. Could somebody please explain?

Dilbert said: "the calcium phosphate is the low temp; the bicarb the higher temp agent. "

That doesn't make any sense to me. Bicarbinate of Soda is baking soda, which is included in all baking powder (if baking soda was the high temp agent, then all baking powders would be double acting). The calicum phosphate and bicarb are supposed to react *together* at low temp to produce carbon dioxide. According to the wikipedia article on baking soda: "Most modern baking powders are double acting, that is, they contain two acid salts, one which reacts at room temperature ... and another which reacts at a higher temperature" Baking soda is not an acid salt. The Rumford baking powder only has one acid salt in it (calcium phosphate) and thus cannot be double acting (right?)

As far as the expiry date, I think that may well have been the problem. The expiration date was 2003, but I thought it was still ok b/c when I put some of it in water, it fizzled. I just bought some new baking powder today and I tried putting the new stuff in the same amount of water and there was a significant difference in the amount of fizzling.

you're right on that point. fascinating topic as I researched it a bit more.

some baking powders have multiple acid compounds - Rumford (and others) curiously have one - but seems to work in a double acting manner. so apparently the precise chemical compound is critical to the double acting effect.

aluminum compounds are common; depending on the viewpoint of the writer, aluminum compounds get blasted for "bitter taste" and "makes your brain go south" (i.e. the alleged link between aluminum and Alzheimer's)

Rumford (and others) curiously have one - but seems to work in a double acting manner.

I remain skeptical. I have yet to see it work in a double acting manner. I decided to test this out. I have placed 1 tsp of baking powder into 1/2 cup of water in a bowl at room temperature to completely react all of the low temp agent. I did this for both Rumford baking powder as well as Clabber Girl baking powder (which contains Sodium Aluminum Sulfate high temp agent). When I get home tonight, I will filter out the baking powder and then put it in some boiling salt water to see if it fizzles. Theoretically the high temp agent will not have reacted yet and I should see a reaction when I put it in the boiling water. I don't know if boiling water is a the right temperature, but if the Clabber Girl powder fizzles and the Rumford doesn't, then I would suspect that the "Double Acting" property of the Rumford powder is marketing BS.

Dilbert wrote:

so apparently the precise chemical compound is critical to the double acting effect.

I am responding to this old thread, as I was researching the same topic.

The Frequently Asked Questions section on Clabbergirl.com has the answers I was looking for.

"Q. Baking powder vs. baking soda – What's the difference?
A. Baking soda is pure bicarbonate of soda also known as sodium bicarbonate it is an alkaline ingredient, and when mixed with acidic ingredients, it reacts and releases bubbles of carbon dioxide. It also has household uses.

Baking powders are leaveners used for cooking. They are made up of sodium bicarbonate (baking soda); an acid salt which reacts with moisture or heat, or both – such as tartaric acid, mono-calcium or combination of acid salts; and cornstarch (an inert filler used to keep ingredients separated).

Q. What is the difference between Baking Powders?
A. Baking Powders differ in their reaction to moisture and heat depending on their formulation. Rumford Baking Powder's reaction is approximately 70% with moisture (or in the bowl) and the rest when heat is applied. Clabber Girl's reaction is approximately 40% with moisture and the rest when heat is applied. Some people prefer the Rumford brand because it does not contain the acid ingredient sodium aluminum sulfate.

Q. What is double acting baking powder?
A. The double action in baking powder means that the baking powder reacts twice, once in the bowl when moisture is applied and again when heat is applied. Almost all baking powders have been double acting for at least 100 years, so you can be confident that all consumer recipes that require baking powder call for double acting baking powder.

Q. Clabber Girl Baking Powder
A. Clabber Girl Baking Powder is a product designed to produce leavening in baked goods by the reaction of baking soda and acid ingredients. This reaction produced carbon dioxide (CO2) bubbles that provide lift, and tenderness, making foods more palatable.
It is composed of cornstarch (to keep active ingredients separated), sodium bicarbonate (baking soda, an alkaline), and acid ingredients sodium aluminum sulphate (reacts with soda when heated) and monocalcium phosphate (reacts with soda when combined with moisture).

Q. Reaction of Rumford Baking Powder (not single-acting but double-acting)
A. Rumford Baking Powder contains only monocalcium phosphate as a leavening acid. Due to the nature of how this acid releases carbon dioxide gas with sodium bicarbonate in the presence of moisture, two-thirds of the available gas is released within approximately two minutes.

It then becomes dormant at room temperature due to the generation of an intermediate form of dicalcium phosphate during the initial mixing. This stage of the reaction contains only one hydrogen ion and requires the catalyst of heat above 140 degrees F. in the batter."

In my opinion, the main difference is in how long you can mix before baking. If you are making something like pancake batter that you may not use immediately, a baking powder with a separate high-temperature ingredient like Clabber Girl will work better.