This week I received a great question: What is cream of tartar exactly? And what is its shelf life? I'm especially glad the last part of the question was asked, as I know that unless you have a major meringue obsession, your cream of tartar has very likely been hanging around in your pantry for some time. 
I talked about cream of tartar briefly last week as a substitute dry acid that can be combined with baking soda to create homemade baking powder. So we all know it is acidic. And most of you are familiar with its use as a stabilizing agent beaten with egg whites for meringues, boiled icing, and other yummy recipes. But just where does that magical white powder originate? If you guessed the land of baking fairies, you are wrong.
The simple answer is: a wine vat!
What? Your curiosity isn't satisfied yet? Well, read on.
Cream of tartar is a chemical known as potassium hydrogen tartrate.
It contains an extremely high amount of potassium: 7 teaspoons would satisfy your nutritional need for potassium for the day. Of course, most recipes call for small amounts.
Cream of tartar is largely composed of tartaric acid that initially forms as reddish-brown crystals on the sides of wine vats known as argol or beeswing. Yummy. The argol is purified and processed with potassium hydroxide to neutralize some of the acidity of the tartaric acid to make it the oh-so-useful pH of the cream of tartar we all know and love!
The acidity and high potassium level make it a popular home remedy for everything from fighting infections to quitting smoking. It also plays a large role in traditional Cajun folk medicine, where it is added to lemonade to 'thin' or 'cleanse' the blood. Muddy's endorses its many applications in the culinary world!
Most of the uses of cream of tartar that we know today were developed by French chefs after 1769, when a Swedish chemist discovered a way to manufacture cream of tartar that would eventually make it readily available to the public.
Cream of tartar's use in the world of desserts includes:
- playing a major role in the formulation of both homemade and commercially produced baking powders
- stabilizing beaten egg whites, encouraging increased volume and heat resistance
- candy and icing making, acting as an 'interfering agent' to discourage the crystallization of sugar
- and Snickerdoodles, which gain a tangy flavor from the cream of tartar while also benefitting from the inhibition of sugar crystallization. This is how they achieve their signature oh-so-chewy chewiness!
While I mourn the fact that we won't see Snickerdoodles at Muddy's until Christmas in July, let's talk about the science behind how cream of tartar helps interacts with egg white. Actually first let us daydream about Muddy's Hot Chocolate Cupcakes (chocolate cake + boiled icing), which feature this egg white/cream of tartar interaction, and will also be featured at Christmas in July! Woo!
Egg white is composed of 90% water and 10% protein, including a protein known as albumin. When beaten, albumin protein strands unfold and get tangled with their neighbors, forming a fluffy matrix of egg protein and air bubbles. Egg whites are very alkaline, so adding an acid like cream of tartar completely changes the albumin's electrical charge, causing it to interact differently with its fellow proteins. The acid makes them more eager to uncurl and build a foam faster. Meanwhile, the potassium hydroxide (remember that chemical added to the tartaric acid to neutralize it a bit in the cream of tartar manufacturing process?) introduces hydrogen ions to the egg whites, which edge their way between all those proteins and discourage them from building TOO tight of a structure. This prevents the egg proteins from getting so snug that they squeeze out all of the water and air necessary for a beautiful, voluminous foam, and thus collapsing like they do when overbeaten until 'dry.'
While cream of tartar stabilizes egg whites, it breaks down sugars used in making candy, heated icings, and other hot, sweet, deliciously smooth things. Your common household granulated sugar is sucrose, which REALLY wants to bond with its fellow sucrose friends and form hard crystals. When you REALLY don't want your sucrose to be all buddy-buddy with its neighbors, adding an interfering agent like cream of tartar breaks down sucrose into its two components of fructose and glucose. Fructose and glucose have no interest in forming hard crystals, so the end product is smooth and free from crystallization.
Muddy's incomparably marshmallowy Boiled Icing relies on cream of tartar for both its interfering role in keeping the sugars smooth and creamy, as well as its stabilizing effect on the egg whites that create the icing's fairy-light structure. Watch our case this spring for some of our flavors featuring this icing: the Old-Fashioned Cupcake (boiled icing + chocolate cake, with a maraschino cherry on top) and the White Tie (boiled icing + chocolate cake rolled in coconut)! Snickerdoodles, as mentioned previously, also use this interaction between their sugars and cream of tartar to make a soft chewy cookie every time.
And now, as a reward for sticking with me through all that science, here is the practical answer everyone can use. And it's a good one! What's the shelf life of cream of tartar? It's basically indefinite! So long as it is kept dry, that is, so keep that lid on tight!
So you all have your assignments for the week. Make some cookies with cream of tartar. Throw a party. Serve your cookies, and serve some cookies from Muddy's Bake Shop, too!
Happy stabilizing ... and interfering!
