While the more familiar “citric acid” may bring to mind the tartness of a lemon, the monohydrate form (i.e., containing a water molecule) is a specific crystalline form used in food, beverage, pharmaceutical, personal care and industrial-cleaning applications.
What is Citric Acid Monohydrate?
Definition & Chemical Identity
Citric acid monohydrate consists of citric acid molecules bonded with one water molecule, forming C₆H₈O₇·H₂O crystals.
Key identifiers:
- CAS Number: 5949-29-1
- E-Number (food additive): E330
- The “monohydrate” designation indicates one water molecule per citric acid molecule and results in slightly different physical properties compared to the anhydrous form.
Why the Monohydrate Form Matters
While citric acid anhydrous and monohydrate both perform similar chemical functions (acidification, chelation, pH regulation), the monohydrate form can differ in terms of moisture content, crystal habit, solubility behavior, handling, storage characteristics and cost. For many food and beverage applications, the monohydrate form is preferred because its crystalline form is more stable and it may hydrate or dehydrate under certain conditions.
Physical & Chemical Properties
Below is a summary table of key properties of citric acid monohydrate.
| Property | Value (approx.) | Notes |
| Molecular formula | C₆H₈O₇·H₂O | Monohydrate form |
| Molecular weight | ~210.14 g/mol | Slightly higher than the anhydrous form (~192 g/mol) |
| Appearance | Colourless crystals or white crystalline powder | Efflorescent in dry air |
| Density | ~1.54 g/cm³ (monohydrate) | At 20 °C |
| Melting/Decomposition point | ~135-152 °C (depending on source) | Loses water / decomposes |
| Solubility in water | Very high; for example 1630 g/L at 20 °C reported | High solubility aids rapid dissolution |
| pKa values | ~3.13, 4.76, 6.4 (for citric acid) | Useful for buffering in formulations |
These properties make the material useful in a wide variety of settings: its high solubility, strong acidity, chelating capabilities and crystalline stability mean that it can function in foods, pharmaceuticals and industrial processes.
Production & Manufacturing
Raw Materials & Microbial Fermentation
Commercial citric acid (including the monohydrate form) is most often produced by fermentation of carbohydrate substrates (such as molasses, glucose syrup) using a mold like Aspergillus niger. After fermentation, the acidic broth is clarified, purified and crystallised.
Crystallisation to Monohydrate Form
The production of the monohydrate form typically involves cooling of a concentrated citric acid solution under controlled conditions so that the crystallised form includes a water molecule in the lattice. Some of the key steps:
- Removal of solids and purification of fermentation broth
- Concentration of the solution
- Cooling/seed crystallisation to promote the monohydrate form
- Separation of crystals (centrifuge or filtration)
- Drying under controlled conditions to maintain monohydrate content
Anhydrous vs. Monohydrate – Key Differences
While both forms serve similar chemical functions, they differ in moisture content, handling, solubility behaviour and storage aspects. The monohydrate may be better suited when a slight moisture content is acceptable or beneficial (e.g., in direct compression tablets, some foods) whereas the anhydrous form may be preferred when restrictions on water content exist.
Applications and Uses
The strength of citric acid monohydrate lies in its broad range of applications across industries. We’ll explore major sectors and typical uses.
Food & Beverage Industry
In food and beverages, it is used as:
- an acidifier to provide tartness/sourness (e.g., soft drinks, candies)
- a preservative (lowering pH to inhibit microbial growth)
- a flavour enhancer or modulator
- Chelating agent stabilizing metal ions in processed foods.
- a component in effervescent drink formulations (in combination with sodium bicarbonate)
Examples include: fruit juices, soft drinks, confectionery, jams, jellies, and preserved fruits.
Pharma & Nutraceutical Uses
Citric acid monohydrate is used as:
- an excipient to improve taste, solubility, stability of active pharmaceutical ingredients (APIs)
- a pH adjuster in solutions and oral dosage forms
- a chelating agent in certain formulations
Personal Care & Cosmetics
In personal care, roles include:
- pH regulation of skin-care and hair care products
- Chelation of metal ions (which could destabilise formulations)
- Mild exfoliating agent (via acid hydrolysis of stratum corneum)
- Support for preservation systems in cosmetics
Industrial & Cleaning Applications
In industrial or cleaning contexts, citric acid monohydrate functions as:
- a descaling/limescale removal agent (chelates calcium/magnesium)
- a pH regulator and chelator in water treatment systems
- a green alternative to harsher acids in cleaning and metal passivation
Summary of Typical Applications
Applications of Citric Acid Monohydrate Across Industries
| Industry | Primary Uses | Key Functional Benefits |
| Food & Beverage | Soft drinks, confectionery, jams, jellies | Acidification, flavour, preservation, chelation |
| Pharmaceutical/Nutraceutical | Tablets, effervescent forms, buffers | pH control, taste improvement, solubility enhancement |
| Personal Care & Cosmetics | Shampoos, lotions, exfoliants | pH regulation, chelation, mild acid hydrolysis |
| Industrial / Cleaning | Water treatment, descaling, cleaning agents | Calcium/magnesium chelation, acid treatment, eco-friendly alternative |
Choosing the Right Grade & Form for Your Application
When selecting citric acid monohydrate for your specific application, several factors must be considered.
Purity & Grade
Different grades are available: food-grade (FCC or equivalent), pharmaceutical grade (USP/Ph Eur), industrial grade (for cleaning, water treatment). The required grade depends on your application’s regulatory needs and end-product use.
Form & Particle Size
Forms may include crystals, powder, granules. Particle size and bulk density impact dissolution rate, flowability, compressibility (in tablets) and mixing behaviour. For example, a fine powder may dissolve quickly but also may be dusty or harder to handle.
Moisture Content & Hydrate Form
Monohydrate vs. anhydrous: If your process is sensitive to moisture (e.g., dry blends, direct compression tablets), you might prefer the anhydrous form. If moisture is less critical or a small water content is acceptable, the monohydrate could be fine. Evaluate the water content, hygroscopicity, and stability under your storage/processing conditions.
Solubility & Processing Conditions
Because citric acid monohydrate is very water-soluble, processing conditions – temperature, dissolution time, mixing – need to be managed. If you’re dissolving it in large quantities, note that solubility increases with temperature. For example: 59.2% w/w at 20 °C and ~84.0% at 100 °C.
Compatibility & Regulatory Requirements
Check that the grade meets regulatory standards relevant to your region and industry (e.g., food additive E330, USP/Ph Eur for pharma) and ensure compatibility with other ingredients in your system (pH, chelation, ionic strength).
Storage, Handling & Stability
Because the monohydrate form can lose water under dry conditions (effloresce) and the anhydrous form can absorb moisture (hygroscopic), storage and handling are critical. Use sealed containers, desiccated or controlled atmosphere as needed.
Safety, Storage & Environmental Aspects
Safety & Handling
While relatively safe compared to many industrial chemicals، citric acid monohydrate nonetheless requires proper handling:
- A mild acid that can irritate skin or eyes.
- Dust may create inhalation hazards in poorly ventilated areas.
- Ensure good industrial hygiene, protective equipment (PPE) if dust is present or large volumes handled.
Storage Conditions
- Store in cool, dry, well‐ventilated area.
- Keep containers sealed to avoid moisture uptake or loss.
- Protect from extreme temperature fluctuations and humidity, which may lead to caking or efflorescence.
- Shelf life varies depending on grade and storage conditions.
Environmental & Regulatory Considerations
- Citric acid monohydrate is biodegradable and considered environmentally friendly in many applications.
- As a food additive (E330) and generally recognised as safe (GRAS) in many jurisdictions, its regulatory burden is relatively modest compared to harsher acids.
- Disposal should still follow local regulations, especially if solutions are at extreme pH or contain other hazardous materials.
SDS (Safety Data Sheet) Highlights
When handling citric acid monohydrate, ensure SDS or MSDS is available. Some key hazard classifications: eye irritation, skin irritation, dust inhalation. Ensure spill control, dust suppression, PPE and first‐aid measures are defined.
Comparative Overview: Monohydrate vs. Anhydrous
Monohydrate vs. Anhydrous Citric Acid: Key Comparison
| Feature | Monohydrate (C₆H₈O₇·H₂O) | Anhydrous (C₆H₈O₇) |
| Molecular weight | ~210 g/mol | ~192 g/mol |
| Water content | ~1 water molecule per acid molecule | 0 water molecules |
| Crystallisation conditions | Tends to crystallise from cold concentrated solutions | Crystallises from hot concentrated solution |
| Moisture/hygroscopic behaviour | Can lose water (effloresce) in dry air | More hygroscopic; tends to absorb moisture |
| Handling implications | Slight moisture content may improve flow/handling in some foods/pharma | Lower moisture ideal for dry blends or when water must be minimised |
| Cost / typical usage | Common in food/beverage grade | Preferred where low moisture is required (e.g., some industrial uses) |
From this comparison, you can see that your choice between monohydrate vs anhydrous depends largely on your downstream process requirements (water content, handling, blending, dissolution).
Market & Cost Considerations
Several factors influence the cost and availability of citric acid monohydrate:
- Availability of carbohydrate feedstocks (molasses, glucose) and fermentation cost.
- Required purity and grade: food, pharmaceutical, or industrial applications.
- Form (crystal size, granulation, powder).
- Logistics and storage conditions (bulk vs packaged).
- Regulatory compliance and certifications (GMP, food safety) increasing cost.
For procurement, consider: negotiating long‐term contracts, verifying supplier certifications, ensuring quality testing (assay, moisture, heavy metals, microbial limits). Also, pay attention to storage conditions: improper storage may lead to product degradation (caking, moisture uptake) and hence hidden costs.
Choosing the Right Application Fit: Practical Guidance
Here are steps you can follow to ensure you’re picking the right citric acid monohydrate form and grade for your application:
- Define application requirements: What industry? What function (acidification, flavouring, chelation, cleaning)?
- Regulatory domain: Food, beverage, pharma, industrial – each has different purity/grade needs.
- Grade selection: Food grade (FCC/E330) vs. pharmaceutical grade vs. industrial.
- Form and granulation: Determine whether crystals, powder, granules are best for your process (dissolution rate, blending, dust control).
- Moisture & hydrate state: Evaluate whether monohydrate is acceptable or anhydrous is required (dry blends, moisture sensitive).
- Supplier verification: Ensure supplier provides documentation (certificate of analysis, SDS, regulatory compliance) and has stable supply.
- Quality check: On-receipt verify assay (≥99 %), moisture content, heavy metals, microbial counts (for food/pharma).
- Storage & handling plan: Develop storage conditions that minimise moisture/humidity risks, dust control, proper ventilation.
- Process integration: Check solubility conditions, mixing/dissolution time, pH impact, compatibility with other ingredients.
- Lifecycle & cost monitoring: Monitor performance, wastage (caked material, off-grade lots), logistic cost, and process impacts (downtime, handling issues).
By following these steps you minimise risk of selecting a sub-optimal form/grade, which might otherwise affect product quality, cost or process efficiency.
Case Studies / Example Scenarios
Scenario A: Beverage Manufacturer – Soft Drink Production
A beverage company wants to introduce a new lemon-flavoured soft drink. They need a tart acidifier to provide flavour, help preserve the drink and ensure good solubility in syrup.
Solution approach: Food grade citric acid monohydrate crystals, good water solubility, known food additive (E330). Choose a crystal or fine powder form for rapid dissolution. Check that moisture content doesn’t elevate total solids and affect shelf-life. Supplier certified to food additive standards.
Outcome: The selected grade dissolves quickly in syrup, delivers consistent pH (target ~2.5–3.0), binds metal ions (improving appearance/stability), and integrates smoothly in production.
Scenario B: Pharmaceutical Tablet Formulation
A pharma company developing an effervescent tablet needs an acid component that dissolves quickly, has reliable assay, low heavy-metal content and good stability in dry blend. The blend is moisture sensitive.
Solution approach: Choose pharmaceutical grade citric acid monohydrate (or possibly anhydrous if moisture is critical). Fine granules, low moisture; include CoA verifying microbes, metals, residuals.
Outcome: The selected grade enables consistent tablet dissolution, predictable acid–base reaction (with sodium bicarbonate), preserved stability in dry packaging, and regulatory compliance.
Scenario C: Industrial Cleaning / Descaling
A water-treatment company needs an acidifier/chelating agent to remove limescale in heat‐exchanger systems. They need bulk quantity, cost‐effective, and the aqueous solution will be diluted at site.
Solution approach: Industrial grade citric acid monohydrate crystals. Bulk price negotiated, grade sufficient for industrial use (less stringent than food/pharma). Ensure good solubility in water, stable storage in large silo or bagged form. On-site handling of dust/residence.
Outcome: The selected product works as a mild acid, chelates calcium/magnesium ions, reduces scale buildup, is more environmentally gentle than strong mineral acids, and is cost-efficient in large volumes.
Common Mistakes & Pitfalls
- Selecting wrong grade: Using industrial grade in food/pharma applications may result in regulatory non-compliance or product recall.
- Ignoring moisture/hydrate differences: Using monohydrate when anhydrous is required for a dry blend may lead to moisture‐related problems (caking, stability).
- Ignoring dissolution behaviour: A coarse crystal may dissolve more slowly than needed, affecting processing times.
- Under-estimating storage/hygroscopicity: Poor storage leads to moisture uptake or caking, reducing efficacy or complicating handling.
- Neglecting supplier documentation: Lack of certificate of analysis, regulatory compliance or quality assurance increases risk of sub-standard lots.
- Misjudging cost vs performance: Choosing cheapest option without checking usability, solubility, quality may increase overall cost via downtime, re-work, wastage.
Future Trends & Innovation
Bio-derived vs synthetic feedstocks: While most citric acid is produced by fungal fermentation of sugar‐based feedstocks, there is increasing interest in using waste biomass or alternative substrates to reduce environmental footprint.
Improved crystal forms: Manufacturers are refining granulation, particle size distribution and flow properties to better meet direct compression tablet demands or rapid dissolution needs.
Green cleaning applications: As industries seek eco-friendly chemicals, citric acid is gaining traction as an alternative to harsher mineral acids for descaling and cleaning.
Precision use in functional foods/nutraceuticals: With increasing demand for functional ingredients, citric acid monohydrate is being integrated in formulations where taste, pH, stability and mineral chelation are critical.
Circular economy & waste reduction: Some producers are re-using mother liquors, improving fermentation yields, and reducing waste streams to lower cost and support sustainability.
Conclusion
Citric acid monohydrate is a remarkably flexible and valuable chemical, with applications spanning food & beverages, pharmaceuticals, personal care, industrial cleaning and more. Its defining characteristics – strong acidity, excellent solubility, chelation ability and crystalline stability – make it a go-to ingredient in many formulations and processes.
However, successful use depends on selecting the right grade, form and supplier, ensuring compatibility with your process, enforcing proper storage & handling, and understanding the full lifecycle cost (including storage, dissolution, handling, logistics).
If you follow the logical steps outlined—define your application needs, verify regulatory requirements, choose the right grade/form, ensure supplier quality, manage storage & handling—you’ll maximise performance, minimise risk and optimise cost.