Cream of tartar (potassium bitartrate) is an acid byproduct of wine production with multiple baking applications: stabilizing whipped egg whites, activating baking soda, and adjusting pH in recipes. Understanding its chemistry explains why it works and when it’s essential versus optional.
What Is Cream of Tartar?
Cream of tartar is potassium bitartrate (KC₄H₅O₆), a mildly acidic salt derived from grape juice sediment during wine fermentation. It’s naturally occurring and completely safe—a GRAS (Generally Recognized as Safe) food ingredient with no controversial aspects. Despite its name, it contains no cream (hence the somewhat misleading name). It’s a white crystalline powder with slightly tart taste and no particular smell. It’s inexpensive and widely available in grocery stores, typically in the baking section.
Cream of tartar represents about 1% of wine production byproducts. During wine fermentation, tartaric acid (naturally present in grapes) combines with potassium from grape skins, forming potassium bitartrate crystals that precipitate (settle out). These crystals are collected, purified, and sold as cream of tartar for baking and cooking applications.
Wine Production Source
When grapes ferment into wine, yeast consumes sugars. The process releases tartaric acid naturally present in grape juice. This acid doesn’t dissolve in the alcoholic liquid; instead, it precipitates as crystals, particularly when temperature is cool. These crystals form the grainy sediment in wine bottles—this is potassium bitartrate. Wine producers remove this sediment (called “tartrates”) through cold precipitation and filtration. The removed crystals are collected, refined, and sold as cream of tartar.
This is why cream of tartar is sometimes called “wine crystals” or “argol.” The connection to wine explains why it’s been a culinary ingredient for centuries—wine producers literally had it as a byproduct and discovered its usefulness in cooking and baking.
Egg White Stabilization Mechanism
Egg whites contain proteins (primarily ovalbumin) that denature and coagulate when whipped, trapping air and forming stable foam. However, the proteins are pH-sensitive—in neutral or slightly basic conditions, they’re prone to overbeating (coagulation becomes too aggressive, liquid separates). Cream of tartar is acidic, lowering pH. The slightly acidic environment stabilizes protein coagulation, allowing whipping to continue further before breakdown occurs. Acidic pH creates tighter, more stable protein networks, resulting in meringue that’s resistant to weeping (liquid separation) and more structurally stable.
The practical effect: egg whites with cream of tartar can be whipped to stiffer peaks without the grainy, separated texture that occurs with plain egg whites whipped to the same extent. Additionally, acidic conditions accelerate foaming—the protein coagulation happens faster with acid present.
Why It Creates Stable Meringue
Meringue is whipped egg whites (and optionally sugar). Without cream of tartar, meringue peaks soften quickly as proteins continue breaking down. With cream of tartar, meringue maintains stiff peaks and resists weeping during storage. The stabilized proteins create a matrix that traps water effectively, preventing liquid from separating. Baked meringue (like meringue pie topping) particularly benefits from cream of tartar—the baked structure is more stable and less prone to collapse during cooling.
The typical ratio is 1/8 teaspoon cream of tartar per egg white. This small amount provides sufficient pH adjustment to noticeably improve stability. Bakers often include cream of tartar even in simple whipped egg white preparations because the improvement in stability is substantial relative to the minimal ingredient addition.
Other Baking Applications
Baking powder: Cream of tartar is the acid component in single-acting baking powders (combined with baking soda and cornstarch). It activates baking soda immediately when liquid is added, making single-acting powder useful for recipes requiring immediate leavening. Baking soda activation: In recipes with baking soda but no other acid, cream of tartar can provide the acid needed to activate the soda: baking soda + cream of tartar → CO₂ + other products. pH adjustment: In some recipes, a small amount adjusts pH to optimize color or texture development.
Additionally, cream of tartar can prevent crystallization in candies and frosting through its effect on sugar solution pH. It’s used in small quantities in candy-making and sugar-work applications where crystal structure matters.
Substitutions & Alternatives
For egg white stabilization: Lemon juice or white vinegar can partially substitute (both acidic), using approximately 1/8 teaspoon per egg white. However, the taste difference is noticeable—lemon/vinegar impart flavor while cream of tartar is tasteless. Copper bowls (when whisking) traditionally stabilize egg whites through chemical interaction, though this method is less reliable than acid. For baking soda activation: Buttermilk, yogurt, lemon juice, or vinegar can provide the acid, though they also change recipe moisture and flavor profiles.
True substitution often isn’t ideal because cream of tartar’s tastelessness is a major advantage. If unavailable, alternatives exist but introduce flavor or texture changes. Omitting entirely is possible in many applications (egg whites whip without cream of tartar, just less stably), but the improvement provided justifies including it when available.
Practical Usage Tips
Storage: Cream of tartar stores indefinitely in airtight container away from moisture. Unlike baking soda/powder which degrade, cream of tartar is chemically stable. Measurement: Use precise measuring spoons (filled level, not heaped) because quantity matters—too much creates slightly unpleasant taste. With egg whites: Add cream of tartar before whipping (while egg whites are still liquid), or add once soft peaks form. As baking soda acid: Mix with dry ingredients before adding liquid, or dissolve with liquid before adding to dough/batter.
Quality indicator: Cream of tartar should be white/off-white powder with no discoloration. Brownish color suggests contamination or age degradation. Reliable brands consistently available in grocery stores ensure quality. Its low cost makes buying fresh periodically reasonable for bakers using it frequently.