Potassium Bitartrate, Potassium Acid Tartrate, Potassium Hydrogen Tartrate, Tartar Cream, E336, 868-14-4

Potassium Bitartrate, Potassium Acid Tartrate, Potassium Hydrogen Tartrate, Tartar Cream, E336, 868-14-4

Potassium Bitartrate (Cream of Tartar) - In-Depth Technical and Industrial Analysis

This document aims to provide a comprehensive technical examination of Potassium Bitartrate (Cream of Tartar), ranging from its chemical identity and production processes to its physicochemical properties and vast array of applications.

Section 1: Identity and Definition

Potassium Bitartrate is an acidic potassium salt of the organic acid Tartaric Acid (specifically the L(+)-Tartaric Acid isomer). Commonly known as Cream of Tartar, it is one of the most well-known by-products of the winemaking industry.

• Chemical Name: Potassium Hydrogen Tartrate

• Common Names: Cream of Tartar, Tartar, Tartaric Acid, Monopotassium Salt, Baking Powder (as a component), Argol (crude form).

• Molecular Formula: C₄H₅O₆K

• Molecular Weight: 188.176 g/mol

• CAS Number: 868-14-4

• EINECS Number: 212-769-1

• Food Additive Code: E 336 (ii) - Classified as Potassium Bitartrate.

• Pharmacopoeia Names: Potassium Bitartrate (USP, BP, Ph. Eur.)

IUPAC and Systematic Names:

• Potassium 3-carboxy-2,3-dihydroxypropanoate (Structural naming)

• Potassium hydrogen (2R,3R)-2,3-dihydroxybutanedioate (Indicates optical isomerism)

• Butanedioic acid, 2,3-dihydroxy- (2R,3R)-, potassium salt (1:1) (Systematic organic chemistry name)

Section 2: Production Process and Origin

The production of Cream of Tartar is not a synthetic chemical process but rather a natural separation and purification process. Its primary source is grapes and wine.

2.1. Formation Mechanism (In the Wine Barrel)

1. Initiation: Grape must naturally contains high concentrations of Tartaric Acid and Potassium ions.

2. Fermentation: As alcoholic fermentation progresses, the ethanol concentration in the medium increases. Potassium Bitartrate is less soluble in a water-ethanol mixture than in pure water.

3. Supersaturation and Precipitation: Due to decreased solubility and lower temperatures (especially during winter), the solution becomes supersaturated with Potassium Bitartrate.

4. Crystallization: The excess Potassium Bitartrate precipitates and crystallizes, forming a hard, crystalline deposit on the bottom and walls of wine barrels. This crude, often reddish-colored deposit is called "Argol" or "Wine Tartar."

2.2. Purification and Refining (From Argol to Cream of Tartar)

The crude argol collected from barrels is purified through the following steps:

1. Mechanical Cleaning: Argol is separated from large particles and barrel residues.

2. Dissolution and Crystallization: The crude argol is dissolved in hot water. The solution is then passed through filters (e.g., cellulose or diatomaceous earth) to remove color-imparting compounds (polyphenols, anthocyanins) and other impurities (dead yeast cells, proteins).

3. Acid Treatment (Optional): To obtain an ultra-pure product, the filtered solution may be treated with dilute hydrochloric acid (HCl) or sulfuric acid (H₂SO₄) . This process helps remove other metal ions (like calcium) and controls the solubility to facilitate re-crystallization, yielding higher purity.

4. Drying and Milling: The resulting pure white crystals are dried under controlled temperatures and milled into a fine powder or granular form suitable for commercial use. The final product typically has a purity of 99.0% - 99.9% .

Section 3: Physical and Chemical Properties (Detailed)

The functionality of Potassium Bitartrate stems directly from these fundamental properties.

3.1. Physical Properties

• Appearance: White, crystalline, free-flowing powder or granules.

• Odor: Characteristic, with no distinct odor other than a faintly acidic note.

• Taste: Cooling, sharp, and pleasantly acidic taste.

• Bulk Density: Typically ranges from 0.8 - 1.0 g/cm³ for powder form.

• True Density: 1.984 g/cm³ (for crystalline structure at 18°C).

• Melting Point: Does not melt as a pure substance; it begins to decompose (pyrolysis) upon heating above approximately 250°C.

3.2. Chemical and Solubility Properties

• Solubility (g/100 mL):

  • Cold Water (20°C): Approx. 0.4 g / 100 mL (Low solubility)

  • Hot Water (100°C): Approx. 6.0 g / 100 mL (Solubility increases significantly with temperature)

  • Ethanol: Insoluble.

  • Dilute Mineral Acids (HCl, HNO₃): Soluble (due to the formation of tartaric acid).

  • Alkaline Solutions (NaOH, KOH): Readily soluble, converting into neutral or basic tartrate salts.

• pH Value:

  • 1% aqueous solution: pH 3.4 - 3.5 (Weakly acidic character).

  • This pH makes it ideal for buffer solutions.

• Stability:

  • Chemical Stability: Highly stable under normal storage conditions (25°C, 60% humidity). It is not hygroscopic (does not readily absorb moisture from the air).

  • Light Stability: Shows no significant photochemical degradation unless exposed to prolonged, direct sunlight, which may cause slight yellowing over a very long period.

  • Thermal Stability: At high temperatures (>220°C), it caramelizes and decomposes into pyrolysis products.

• Solution Behavior (Buffering Capacity): When dissolved in water, Potassium Bitartrate establishes an equilibrium between a weak acid (tartaric acid) and its salt (potassium bitartrate). This creates an effective buffer system, particularly in the acidic range (pH 3.0-4.0). If a strong base is added, the acidic hydrogen (H⁺) in the solution neutralizes it, preventing a rapid increase in pH.

Section 4: Applications - Technical and Functional Analysis

The versatility of Potassium Bitartrate is based on its core properties: acidic nature, low solubility, and buffering capacity.

4.1. Food Industry - Functional Classification

1. Baking Powder System (Acidulant):

   • Function: It reacts with sodium bicarbonate (baking soda) to produce CO₂ gas for leavening.

   • Reaction Rate: Classified as a "fast-acting" acid. It begins reacting immediately upon contact with cold liquid. Therefore, in commercial baking powders, it is often combined with other acids (like Sodium Aluminum Phosphate or Sodium Acid Pyrophosphate, which are heat-activated) to provide a double-acting leavening effect—initial reaction at mixing and secondary reaction in the oven.

   • Application: Preferred in quick-bake items like cakes, pancakes, biscuits, and muffins where immediate lift is desired.

2. Stabilizer and Crystallization Inhibitor:

   • Egg White Stabilization (Meringue): It delays the denaturation (coagulation) of proteins (albumin) in egg whites. By providing an acidic environment, it allows the proteins to unfold more slowly and form a stronger, finer, and more stable foam network. This results in a meringue that is more voluminous, glossy, and holds its shape better. It also helps prevent excessive browning during baking.

   • Sugar Syrups (Invert Sugar): It prevents the crystallization of sucrose (table sugar). In an acidic environment, sucrose hydrolyzes into glucose and fructose, a mixture known as invert sugar. Invert sugar has a much lower tendency to crystallize. This property is crucial for maintaining the fluidity of syrups (e.g., in confectionery creams, candies, and beekeeping winter feed).

3. Acidity Regulator and Buffer:

   • Function: Lowers the pH of food products or helps maintain a stable pH within a specific range (3.0-4.0).

   • Application: Used in jellies, jams, fruit preserves, candies, soft drinks, and some dairy products. It helps inhibit microbial growth (antimicrobial effect) and maintains the desired tart flavor profile.

4.2. Industrial and Technical Applications

1. Metal Plating and Surface Treatment (Galvanotechnics):

   • Function: Acts as a complexing agent (chelating agent) in electroplating baths, particularly for tin and copper.

   • Mechanism: It forms soluble complexes with metal ions (e.g., tin Sn²⁺). This ensures the even distribution of metal ions in the bath, leading to a smoother, finer-grained, and brighter metal deposit on the object being plated. It also helps in cleaning the oxide layer from the metal surface prior to plating.

   • Coloring: Can be used in chemical coloring processes on metals like aluminum.

2. Analytical Chemistry (Buffer Solution):

   • It is a primary component in the preparation of standard buffer solutions used for calibration and analysis. The well-known "Tartrate buffer" with a pH of 3.56 at 25°C is a common reference point for calibrating pH meters.

3. Ceramics and Glass Industry:

   • Can be used as a flux in the production of glazes and glass. Its alkali metal content helps lower the melting point of the mixture and can influence the hardness and finish of the surface.

4.3. Medical, Pharmaceutical, and Biological Applications

1. Laxative (Purgative) Mechanism of Action:

   • Form: Often used in suppository form, combined with sodium bicarbonate.

   • Mechanism: Upon contact with the moisture in the rectum, a chemical reaction occurs between the acidic Potassium Bitartrate and the basic Sodium Bicarbonate:
     HC₄H₄O₆K (acid) + NaHCO₃ (base) → KNaC₄H₄O₆ (soluble salt) + H₂O + CO₂ (gas)

   • Physiological Effect: The rapid release of carbon dioxide gas creates sudden distension (stretching) of the rectal wall. This mechanical stimulation activates mechanoreceptors, triggering a reflex contraction (peristalsis) of the lower bowel, leading to defecation. This is classified as a mechanically acting, stimulant laxative.

2. Pharmaceutical Excipient:

   • Used as a buffering agent in some drug formulations to adjust the solubility or stability of the active pharmaceutical ingredient.

   • In effervescent tablets or powders, it reacts with carbonate/bicarbonate sources to facilitate rapid dissolution and create a pleasant-tasting, fizzy solution.

3. Biomedical Research Potential (Preliminary Findings):

   • Anti-Cancer Research: Recent in-vitro (laboratory, cell culture) studies suggest that tartrate compounds may exhibit antiproliferative effects (inhibiting growth) on certain cancer cell lines, particularly breast cancer. The proposed mechanism involves potential interference with intracellular signaling pathways or epigenetic mechanisms (such as DNA methylation). It is crucial to emphasize that these are preliminary findings and do not constitute sufficient evidence for use as a cancer treatment in humans. Research in this area is ongoing and exploratory.

4.4. Household and Other Uses

• Natural Cleaning Agent: When mixed with vinegar or lemon juice, it forms a mildly abrasive paste. This paste is effective for cleaning stubborn stains, tarnish, and limescale from stainless steel, copper, brass, and other kitchen utensils. It can also be used to clean grout between ceramic tiles.

• Beekeeping: As mentioned earlier, it prevents crystallization in the sugar syrup (typically a 2:1 ratio of sugar:water) used to feed honeybees during winter. This ensures the bees can easily access this critical food source throughout the cold months.

Potasyum Bitartarat (Krem Tartar) – Diğer İsimler / Other Names

Resmi ve Farmakope İsimleri / Official and Pharmacopoeia Names

Sistematik (IUPAC) Kimya İsimleri / Systematic (IUPAC) Chemical Names

Section 5: Safety, Storage, and Regulatory Status

• Safety: Potassium Bitartrate is generally recognized as safe (GRAS status by the FDA). It is non-toxic at the common usage levels found in food. Excessive consumption could potentially cause mild gastric discomfort or electrolyte imbalance in sensitive individuals due to its potassium content.

• Storage: Should be stored in a cool (below 25°C), dry, and well-ventilated area, in its original closed packaging. It should be kept away from strong bases and oxidizing agents. Protection from direct sunlight is recommended. Shelf life under proper conditions is typically 2-3 years.

• Regulatory Status: Approved as a food additive (E 336) in the EU and many other countries. It can be produced to meet Halal, Kosher, and Vegetarian certification standards. Pharmaceutical grades are available that meet USP (United States Pharmacopeia) and EP (European Pharmacopoeia) standards.

Potassium Bitartrate (Cream of Tartar) – CAS Numbers and Other Identifiers