Lactic Acid
Properties
| State | Liquid (viscous) at room temperature in pure form; usually encountered in solution |
| Color | Colorless to yellowish |
| Solubility | Miscible with water |
| Melting Point | 53°C (L-form crystalline) |
| Boiling Point | 122°C (at 12 mmHg) |
About Lactic Acid
Lactic acid is the simplest alpha-hydroxy acid — a carboxylic acid with an OH on the alpha carbon and a methyl group hanging off — and it's the molecule that gives yogurt, sourdough, and aged cheddar their tang. Carl Wilhelm Scheele first crystallized it from sour milk in 1780, and the modern name still carries the Latin lac. The molecule has one stereocenter, so it exists as L-(+)-lactic acid (the form mammalian muscle produces during anaerobic glycolysis) and D-(-)-lactic acid (made by some Lactobacillus strains). Most industrial production now runs through fermentation of corn or beet glucose by engineered Lactobacillus rhamnosus or Bacillus coagulans, hitting yields above 90% on sugar and final titers around 150-200 g/L; the older synthetic route from acetaldehyde + HCN is essentially obsolete because it gives a racemate that PLA polymerization can't use. Global capacity is now over 1.2 million tonnes per year, with roughly 40% going to PLA bioplastics — the polymer that prints on FDM 3D printers as that yellowish, slightly sweet-smelling filament and shows up as compostable cutlery and beverage cups. PLA is hydrolyzed by industrial composting (60°C, 60% humidity) in 60-90 days, but it does not break down meaningfully in a backyard compost bin or at sea — a frequently misunderstood point.
Where you'll encounter it
If you've ever felt the burn at the end of a sprint, eaten a spoonful of Greek yogurt, or printed something on an FDM 3D printer with PLA filament, you've encountered lactic acid. The tang in a bowl of Greek yogurt is Lactobacillus bulgaricus dropping milk pH from 6.7 to 4.5 by converting lactose into L-lactic acid — that drop coagulates the casein protein into the thick gel structure. Open any maker-space FDM 3D printer and the spool of yellowish, slightly sweet-smelling filament feeding into the hot end is polylactic acid polymerized from corn-derived lactic acid. Dermatologists use 5-30% lactic-acid chemical peels to slough dead skin and stimulate collagen, and beef processors spray 2-5% lactic acid on carcasses post-slaughter as a USDA-approved antimicrobial that doesn't leave visible residue.
Common Uses
- Polylactic acid (PLA) feedstock for 3D-printer filament and compostable packaging
- pH adjustment in soft drinks, dressings, and brined vegetables (E270)
- Antimicrobial spray on beef carcasses post-slaughter at 2-5% v/v
- Chemical exfoliant in dermatology peels at 5-30% with controlled pH
- Sourdough and yogurt fermentation product from Lactobacillus cultures
- Plasticizer alternative to phthalates in cellulose-based polymers
- Tanning agent in vegetable-tanned leather processing
Safety Information
Generally recognized as safe for food use (FDA GRAS, FEMA 2611) at typical food-additive levels. Concentrated solutions (≥85%) are corrosive — GHS H315, H318. There is no statutory airborne limit, but the mist carries an advisory one — treat it as an irritant aerosol. Skin peels with concentrated lactic acid are dermatologist-supervised; over-the-counter products cap at around 12% with pH ≥3.5 to limit irritation. Inhalation of vapors from heated lactic acid causes throat and lung irritation — use a fume hood for any work above 80°C.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.