Potassium bitartrate, also known as potassium hydrogen tartrate, with formula K C₄ H₅ O₆, is the

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

acid salt of tartaric acid (a

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...

)—specifically, l-( + )-tartaric acid. Especially in cooking, it is also known as cream of tartar. It is produced as a byproduct of

winemaking Winemaking, wine-making, or vinification is the production of wine, starting with the selection of the fruit, its Ethanol fermentation, fermentation into alcohol, and the bottling of the finished liquid. The history of wine-making stretches over ...

by purifying of the

precipitate In an aqueous solution, precipitation is the "sedimentation of a solid material (a precipitate) from a liquid solution". The solid formed is called the precipitate. In case of an inorganic chemical reaction leading to precipitation, the chemic ...

deposited by fermenting

must Must is freshly crushed Juice, fruit juice (usually grape juice) that contains the skins, seeds, and stems of the fruit. The solid portion of the must is called pomace and typically makes up 7–23% of the total weight of the must. Making must ...

in wine barrels, which arises from the tartaric acid and potassium naturally occurring in grapes. Approved by the FDA as a direct food substance, cream of tartar is used as an additive, stabilizer, pH control agent, antimicrobial agent, processing aid, and thickener in various food products. It is used as a component of baking powders and baking mixes, and is valued for its role in stabilizing egg whites, which enhances the volume and texture of meringues and soufflés. Its acidic properties prevent sugar syrups from crystallizing, aiding in the production of smooth confections such as candies and frostings. When combined with

sodium bicarbonate Sodium bicarbonate ( IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda (or simply “bicarb” especially in the UK) is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cat ...

, it acts as a

leavening agent In cooking, a leavening agent () or raising agent, also called a leaven () or leavener, is any one of a number of substances used in doughs and batters that cause a foaming action (gas bubbles) that lightens and softens the mixture. An altern ...

, producing

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

gas that helps baked goods rise. It will also stabilize

whipped cream Whipped cream, also known as Chantilly cream or (), is high-fat dairy cream that has been aerated by whisking until it becomes light, fluffy, and capable of holding its shape. This process incorporates air into the cream, creating a semi-soli ...

, allowing it to retain its shape for longer periods. Potassium bitartrate further serves as mordant in textile dyeing, as reducer of

chromium trioxide Chromium trioxide (also known as chromium(VI) oxide or chromic anhydride) is an inorganic compound with the formula . It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. This compound is a dark-purple solid ...

in mordants for wool, as a metal processing agent that prevents oxidation, as an intermediate for other potassium tartrates, as a cleaning agent when mixed with a weak acid such as

vinegar Vinegar () is an aqueous solution of diluted acetic acid and trace compounds that may include flavorings. Vinegar typically contains from 5% to 18% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation, converting ...

, and as reference standard pH buffer. It has a long history of medical and veterinary use as a laxative administered as a rectal suppository, and is used also as a

cathartic In medicine, a cathartic is a substance that ''accelerates'' defecation. This is similar to a laxative, which is a substance that ''eases'' defecation, usually by softening feces. It is possible for a substance to be both a laxative and a cathar ...

and as a

diuretic A diuretic () is any substance that promotes diuresis, the increased production of urine. This includes forced diuresis. A diuretic tablet is sometimes colloquially called a water tablet. There are several categories of diuretics. All diuretics ...

. It is an approved third-class OTC drug in Japan and was one of active ingredients in Phexxi, a non-hormonal contraceptive agent that was approved by the FDA in May 2020.

History

Potassium bitartrate was first characterized by Swedish chemist

Carl Wilhelm Scheele Carl Wilhelm Scheele (, ; 9 December 1742 – 21 May 1786) was a Swedish Pomerania, German-Swedish pharmaceutical chemist. Scheele discovered oxygen (although Joseph Priestley published his findings first), and identified the elements molybd ...

(1742–1786). This was a result of Scheele's work studying fluorite and

hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colorless, acidic and highly corrosive. A common concentration is 49% (48–52%) but there are also stronger solutions (e.g. 70%) and pure HF has a boiling p ...

. Scheele may have been the first scientist to publish work on potassium bitartrate, but use of potassium bitartrate has been reported to date back 7000 years to an ancient village in northern Iran. Modern applications of cream of tartar started in 1768 after it gained popularity when the French started using it regularly in their cuisine. In 2021, a connection between potassium bitartrate and canine and feline toxicity of grapes was first proposed. Since then, it has been deemed likely as the source of grape and raisin toxicity to pets.

Occurrence

Potassium bitartrate is naturally formed in grapes from the acid dissociation of tartaric acid into bitartrate and tartrate ions. Potassium bitartrate has a low solubility in water. It

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

lizes in wine casks during the

fermentation Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduce ...

grape A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters. The cultivation of grapes began approximately 8,0 ...

juice Juice is a drink made from the extraction or Cold-pressed juice, pressing of the natural liquid contained in fruit and vegetables. It can also refer to liquids that are flavored with concentrate or other biological food sources, such as meat ...

, and can precipitate out of wine in bottles. The rate of potassium bitartrate precipitation depends on the rates of nuclei formation and

crystal growth Crystal growth is a major stage of a crystallization, crystallization process, and consists of the addition of new atoms, ions, or polymer strings into the characteristic arrangement of the crystalline lattice. The growth typically follows an ini ...

, which varies based on a wine's alcohol, sugar, and extract content. The crystals ( wine diamonds) will often form on the underside of a cork in wine-filled bottles that have been stored at temperatures below , and will seldom, if ever, dissolve naturally into the wine. Over time, crystal formation is less likely to occur due to the decreasing

supersaturation In physical chemistry, supersaturation occurs with a solution (chemistry), solution when the concentration of a solute exceeds the concentration specified by the value of solubility at Solubility equilibrium, equilibrium. Most commonly the term ...

of potassium bitartrate, with the greatest amount of precipitation occurring in the initial few days of cooling. Historically, it was known as beeswing for its resemblance to the sheen of bees' wings. It was collected and purified to produce the white, odorless,

acidic An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen cation, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid. The first category of acids are the ...

powder used for many culinary and other household purposes. These crystals also precipitate out of fresh grape juice that has been chilled or allowed to stand for some time. To prevent crystals from forming in homemade grape jam or jelly, the prerequisite fresh grape juice should be chilled overnight to promote crystallization. The potassium bitartrate crystals are removed by filtering through two layers of cheesecloth. The filtered juice may then be made into jam or jelly. In some cases they adhere to the side of the chilled container, making filtering unnecessary. The presence of crystals is less prevalent in red wines than in white wines. This is because red wines have a higher amount of

tannin Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and Precipitation (chemistry), precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' is widel ...

and colouring matter present as well as a higher sugar and extract content than white wines. Various methods such as promoting crystallization and filtering, removing the active species required for potassium bitartrate precipitation, and adding additives have been implemented to reduce the presence of potassium bitartrate crystals in wine.

Applications

In food

In food, potassium bitartrate is used for: * Stabilizing

egg white Egg white is the clear liquid (also called the albumen or the glair/glaire) contained within an egg. In chickens, it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms a ...

s, increasing their warmth-tolerance and volume * Stabilizing

, maintaining its texture and volume * Anti-caking and thickening * Preventing sugar syrups from crystallizing by causing some of the

sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refined ...

to break down into

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

and

fructose Fructose (), or fruit sugar, is a Ketose, ketonic monosaccharide, simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and gal ...

* Reducing discoloration of boiled

vegetable Vegetables are edible parts of plants that are consumed by humans or other animals as food. This original meaning is still commonly used, and is applied to plants collectively to refer to all edible plant matter, including edible flower, flo ...

s Additionally, it is used as a component of: * Baking powder, as an acid ingredient to activate

baking soda Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda (or simply “bicarb” especially in the UK) is a chemical compound with the formula NaHCO3. It is a salt (chemistry), salt compose ...

* Salt substitutes, in combination with

potassium chloride Potassium chloride (KCl, or potassium salt) is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water, and its solutions have a sa ...

A similar acid salt, sodium acid pyrophosphate, can be confused with cream of tartar because of its common function as a component of baking powder.

Baking

Adding cream of tartar to egg whites gives volume to cakes, and makes them more tender. As cream of tartar is added, the pH decreases to around the isoelectric point of the foaming proteins in egg whites. Foaming properties of egg whites are optimal at this pH due to increased protein-protein interactions. The low pH also results in a whiter crumb in cakes due to flour pigments that respond to these pH changes. However, adding too much cream of tartar (>2.4% weight of egg white) can affect the texture and taste of cakes. The optimal cream of tartar concentration to increase volume and the whiteness of interior crumbs without making the cake too tender, is about 1/4 tsp per egg white. As an acid, cream of tartar with heat reduces sugar crystallization in invert syrups by helping to break down

into its monomer components -

and

in equal parts. Preventing the formation of sugar crystals makes the syrup have a non-grainy texture, shinier and less prone to break and dry. However, a downside of relying on cream of tartar to thin out crystalline sugar confections (like fudge) is that it can be hard to add the right amount of acid to get the desired consistency. Cream of tartar is used as a type of acid salt that is crucial in baking powder. Upon dissolving in batter or dough, the tartaric acid that is released reacts with

to form

that is used for leavening. Since cream of tartar is fast-acting, it releases over 70 percent of carbon dioxide gas during mixing.

Household use

Potassium bitartrate can be mixed with an acidic liquid, such as lemon juice or white vinegar, to make a paste-like cleaning agent for metals, such as

brass Brass is an alloy of copper and zinc, in proportions which can be varied to achieve different colours and mechanical, electrical, acoustic and chemical properties, but copper typically has the larger proportion, generally copper and zinc. I ...

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

, or

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

, or with water for other cleaning applications, such as removing light stains from

porcelain Porcelain (), also called china, is a ceramic material made by heating Industrial mineral, raw materials, generally including kaolinite, in a kiln to temperatures between . The greater strength and translucence of porcelain, relative to oth ...

. This mixture is sometimes mistakenly made with vinegar and

(baking soda), which actually react to neutralize each other, creating

and a

sodium acetate Sodium acetate, CH3COONa, also abbreviated Sodium, NaOxygen, OAcetyl, Ac, is the sodium Salt (chemistry), salt of acetic acid. This salt is colorless, deliquescent, and hygroscopy, hygroscopic. Applications Biotechnological Sodium acetate is u ...

solution. Cream of tartar was often used in traditional

dyeing Dyeing is the application of dyes or pigments on textile materials such as fibers, yarns, and fabrics with the goal of achieving color with desired color fastness. Dyeing is normally done in a special solution containing dyes and particular ...

where the complexing action of the tartrate ions was used to adjust the solubility and

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

of mordant salts such as tin chloride and

alum An alum () is a type of chemical compound, usually a hydrated double salt, double sulfate salt (chemistry), salt of aluminium with the general chemical formula, formula , such that is a valence (chemistry), monovalent cation such as potassium ...

. Cream of tartar, when mixed into a paste with

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

, can be used to clean

rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH) ...

from some

hand tool A hand tool is any tool that is powered manual labour, by hand rather than a motor. Categories of hand tools include wrenches, pliers, cutter (disambiguation), cutters, File (tool), files, hammer, striking tools, chisel, struck or hammered tools, ...

s, notably hand files. The paste is applied, left to set for a few hours, and then washed off with a baking soda/water solution. After another rinse with water and thorough drying, a thin application of oil will protect the file from further rusting. Slowing the set time of

plaster of Paris Plaster is a building material used for the protective or decorative coating of walls and ceilings and for moulding and casting decorative elements. In English, "plaster" usually means a material used for the interiors of buildings, while "re ...

products (most widely used in

gypsum plaster Plaster is a building material used for the protective or decorative coating of walls and ceilings and for Molding (decorative), moulding and casting decorative elements. In English, "plaster" usually means a material used for the interiors of ...

wall work and artwork casting) is typically achieved by the simple introduction of almost any acid diluted into the mixing water. A commercial retardant premix additive sold by USG to trade interior plasterers includes at least 40% potassium bitartrate. The remaining ingredients are the same plaster of Paris and

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

-silica aggregate already prominent in the main product. This means that the only active ingredient is the cream of tartar.

Cosmetics

For dyeing hair, potassium bitartrate can be mixed with henna as the mild acid needed to activate the henna.

Medicinal use

Cream of tartar has been used internally as a purgative, but this is dangerous because an excess of potassium, or

hyperkalemia Hyperkalemia is an elevated level of potassium (K+) in the blood. Normal potassium levels are between 3.5 and 5.0 mmol/L (3.5 and 5.0 mEq/L) with levels above 5.5mmol/L defined as hyperkalemia. Typically hyperkalemia does not cause symptoms. Oc ...

, may occur.

Chemistry

Potassium bitartrate is the United States'

National Institute of Standards and Technology The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into Outline of p ...

's primary reference standard for a pH buffer. Using an excess of the salt in water, a

saturated solution In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...

is created with a pH of 3.557 at . Upon dissolution in water, potassium bitartrate will

dissociate Dissociation in chemistry is a general process in which molecules (or ionic compounds such as salts, or complexes) separate or split into other things such as atoms, ions, or radicals, usually in a reversible manner. For instance, when an aci ...

into acid tartrate, tartrate, and potassium

ions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

. Thus, a saturated solution creates a buffer with standard pH. Before use as a standard, it is recommended that the solution be filtered or decanted between and . Potassium carbonate can be made by burning cream of tartar, which produces "

pearl ash Potash ( ) includes various mined and manufactured salts that contain potassium in water- soluble form.

". This process is now obsolete but produced a higher quality (reasonable purity) than "

potash Potash ( ) includes various mined and manufactured salts that contain potassium in water- soluble form.

" extracted from wood or other plant ashes.