What is Lactic Acid?
Lactic acid (2-hydroxypropanoic acid, C₃H₆O₃, CAS 50-21-5) is an alpha-hydroxy carboxylic acid sold as a clear-to-pale-yellow aqueous liquid. If you buy it for a process line, you are really buying a concentration and a grade: the commodity ships mainly at 80%, 85%, and 88% strength, in technical, food (FCC), heat-stable, and USP qualities, and in three chiral specifications (L(+), D(−), and racemic DL). The molecule is the same; the impurity profile, optical purity, and price are not. Because it carries both a carboxyl (−COOH) and a hydroxyl (−OH) group on adjacent carbons, lactic acid acts as a weak acid (a 10% solution sits around pH 2) and as a polymerizable monomer. That second property is why it has become a large-volume feedstock for polylactic acid (PLA) bioplastic, alongside its long-standing roles in food acidulation, leather tanning, and industrial cleaning.Grades, Concentrations, and How to Specify Them
The most common RFQ error is asking for “lactic acid” without a concentration, grade, and isomer. The table below compares what you will see on a quote. Values are typical reference figures; the CoA for your lot governs.| Grade | Typical assay | Optical form | Reference spec | Primary use |
|---|---|---|---|---|
| Technical / industrial | 80% or 88% | Usually L(+) or DL | Supplier spec | Cleaning, tanning, descaling, pH control |
| Food grade (FCC) | 80%, 85%, or 88% | L(+) preferred | FCC; FDA 21 CFR 184.1061 | Acidulant, preservative, pH adjust |
| Heat-stable food grade | 88% | L(+) | FCC, low-color on heating | Hot-fill, baking, confectionery |
| USP / pharma | 88–90% | L(+) or DL | USP–NF monograph | Pharma excipient, dialysis, hemostasis buffers |
| PLA-grade (polymer) | High-optical-purity | >99% single isomer | Producer spec | PLA / lactide monomer |
Chemical and Physical Properties
Structure and Isomers
The structural formula is CH₃−CH(OH)−COOH. The chiral carbon gives two enantiomers plus the racemate:- L(+)-lactic acid (CAS 79-33-4): the biologically common form; preferred for food and PLA.
- D(−)-lactic acid (CAS 10326-41-7): less common; used in specialty synthesis and some PLA grades.
- DL (racemic) (CAS 598-82-3): a 50/50 mix from synthetic routes; fine for industrial and many food uses.
Physical Data (anhydrous reference)
Molar mass 90.08 g/mol; melting point about 18°C for the racemate and ~53°C for pure L(+) crystals; it is fully miscible with water and ethanol and hygroscopic. Commercial solutions do not freeze near these points because they are aqueous. Specific gravity of an 88% solution is roughly 1.20 at 25°C. The acid is non-volatile and decomposes rather than boiling cleanly at atmospheric pressure.Reactivity Worth Designing For
The dual functionality drives the chemistry: the carboxyl group neutralizes bases and forms lactate salts (calcium, sodium, ammonium lactate); the hydroxyl group lets it esterify and self-condense into lactoyllactic acid and, on dehydration, into lactide, the cyclic dimer that polymerizes to PLA. In aqueous solution lactic acid is mildly corrosive to carbon steel and many metals, so specify 316L stainless steel, HDPE, PP, PVDF, or FRP for wetted parts; avoid mild steel and copper alloys.Production: Fermentation vs Synthesis
Most commercial lactic acid is made by fermentation of carbohydrate feedstocks (corn dextrose, sugarcane, beet sugar, sometimes whey lactose) using Lactobacillus strains, then recovered and purified. Fermentation lets the producer select for a single isomer, which is why fermentation dominates food and PLA supply. A synthetic route runs acetaldehyde and hydrogen cyanide to lactonitrile, then hydrolyzes it to lactic acid; it yields the racemic DL form and is used for some industrial volumes. The practical buyer takeaway: if you need a specified isomer or food/PLA quality, you are almost certainly buying fermentation-derived product, and your supplier should be able to state the carbohydrate feedstock and isomer purity on the CoA.Industrial Applications by Sector
- Food and beverage: acidulant, pH regulator, and preservative in dressings, beverages, confectionery, and meat-surface decontamination; specify FCC grade meeting FDA 21 CFR 184.1061.
- PLA bioplastic: high-optical-purity lactic acid is the monomer; this is the fastest-growing demand pool.
- Cleaning and descaling: a mild organic acid alternative to mineral acids for removing limescale and soap scum; technical 80%/88% is standard.
- Leather and tanning: pickling and deliming baths use lactic acid for controlled pH.
- Personal care (formulation input): used as an exfoliating ingredient and pH adjuster in cosmetic formulations; the formulator, not the raw-material supplier, owns the finished-product claims.
- Pharma: USP-grade lactic acid and lactate salts as excipients and buffers.
Handling, Materials, and Safety
Lactic acid solutions are classified as causing serious eye damage and skin irritation at higher concentrations under GHS; the 88% concentrate is the most aggressive. Specify splash goggles, nitrile gloves, and resistant aprons, and provide eyewash access. Store in HDPE, PP, lined steel, or FRP; keep above its crystallization range in cold climates (concentrated solutions can become cloudy or partially crystallize when chilled, then re-dissolve on warming). It is combustible only at very high temperatures and is readily biodegradable, but treat concentrate spills as a corrosive-liquid event and neutralize with a mild base before disposal under local rules.Regulatory and Transport Snapshot
- FDA: GRAS as a direct food ingredient under 21 CFR 184.1061, referencing Food Chemicals Codex specifications.
- Food Chemicals Codex (FCC): the purity standard food-grade buyers cite.
- USP–NF: pharmaceutical-grade monograph for excipient use.
- REACH: registered in the EU; SDS required from the supplier.
- DOT/transport: dilute solutions are often non-regulated, but concentrated lactic acid may ship as a Class 8 corrosive depending on concentration; verify UN classification for your exact strength and shipment.
Sourcing and RFQ Guidance
To get clean, comparable quotes, state these on your RFQ:- Concentration (80%, 85%, 88%) and acceptable assay window.
- Grade (technical, FCC food, heat-stable, USP, PLA-grade).
- Isomer (L(+), D(−), or DL) and, for polymer use, minimum optical purity.
- Feedstock/origin if you need fermentation-derived or non-GMO documentation.
- Certifications (FCC, USP, Kosher/Halal, ISO 9001 site, FDA 21 CFR 184.1061).
- Packaging (bulk, IBC tote, 250-kg drum, 25-kg can) and annual volume.
- Color/heat-stability spec if the product sees a hot process step.
Frequently Asked Questions (FAQs) about Lactic Acid
What is the CAS number of lactic acid?
The generic CAS number is 50-21-5. The L(+) isomer is 79-33-4, the D(−) isomer is 10326-41-7, and the racemic DL form is 598-82-3.
From the RawSource catalog
Lactic AcidView typical properties & documentation — SDS available on request.
What concentrations of lactic acid are sold commercially?
The most common commercial strengths are 80%, 85%, and 88% aqueous solutions. At 88% the liquid is more viscous and partly self-esterified, so the free-acid titer is lower until diluted.
What is the difference between L, D, and DL lactic acid?
They are the two mirror-image isomers and their 50/50 mixture. L(+) is preferred for food and PLA; DL (racemic) comes from synthetic routes and suits many industrial uses. PLA requires high single-isomer optical purity.
Is lactic acid food grade and FDA recognized?
Food-grade lactic acid is GRAS as a direct food ingredient under FDA 21 CFR 184.1061 and is specified to the Food Chemicals Codex. Confirm the grade and certification documents for your application.
What is lactic acid used to make?
It is a food acidulant and preservative, a feedstock for polylactic acid (PLA) bioplastic, a mild descaling and cleaning acid, a leather-tanning agent, and a formulation input for cosmetics and pharmaceuticals.
What materials are compatible with lactic acid?
Use 316L stainless steel, HDPE, PP, PVDF, or FRP for wetted parts. Avoid mild/carbon steel and copper alloys, which the acid corrodes.
What is the pH of lactic acid?
A 10% solution sits around pH 2; commercial concentrates are strongly acidic. It is a weak acid with a pKa of about 3.86.
Is lactic acid biodegradable?
Lactic acid is readily biodegradable. Note this does not make a concentrated solution non-corrosive; handle the concentrate as a corrosive liquid and neutralize spills before disposal under local regulations.
How is commercial lactic acid produced?
Most is made by fermenting carbohydrate feedstocks (corn dextrose, sugarcane, beet sugar) with Lactobacillus strains, which allows selection of a single isomer. A synthetic route via lactonitrile yields the racemic DL form.
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