Malic Acid
Properties
| State | Solid (white crystalline powder with strong sour taste) |
| Color | White |
| Solubility | Very soluble in water (558 g/L at 20 °C); soluble in ethanol |
| Melting Point | 130 °C (L-form) |
| Boiling Point | Decomposes before boiling |
About Malic Acid
Malic acid is the alpha-hydroxy dicarboxylic acid you taste when you bite into a green apple. Carl Wilhelm Scheele crystallized it from apple juice in 1785 and named it from Latin malum (apple); the L-enantiomer dominates fruit (apples, grapes, cherries, rhubarb) and is the biologically active form, while the racemic DL synthetic material made from maleic anhydride hydration is what mostly shows up on industrial drum labels. The molecule does heavy lifting in two completely separate domains. In intermediary metabolism, L-malate is the Krebs cycle intermediate produced by fumarase from fumarate and oxidized by malate dehydrogenase to oxaloacetate (L-malate + NAD+ -> oxaloacetate + NADH + H+), pumping reducing equivalents into the electron transport chain. The malate-aspartate shuttle uses this same chemistry to ferry cytosolic NADH equivalents across the inner mitochondrial membrane during aerobic glycolysis, which is one reason why malate dehydrogenase deficiency is so quickly lethal. In the wine and food industry, malic acid is what makes Granny Smith apples mouth-puckering and what gets converted to softer L-lactic acid by Oenococcus oeni and Lactobacillus species during the malolactic fermentation that finishes red wines and big white Chardonnays. Winemakers either encourage MLF (most reds, oaked Chardonnay) or block it with SO2 and sterile filtration (Riesling, Sauvignon Blanc) depending on whether the goal is buttery roundness or crisp acidity. Sour-candy formulators love malic acid because its slow taste-release gives the long-lasting pucker that citric acid cannot produce.
Where you'll encounter it
If you have ever puckered through a Sour Patch Kid, tasted the buttery diacetyl note in an oaked Chardonnay that finished MLF, or pipetted L-malate into a coupled NADH-malate dehydrogenase enzyme assay, you have been working with malic acid. Candy formulators dust DL-malic acid on top of a sugar shell because the slow pH drop on the tongue holds the sour signal for 30 to 60 seconds, where citric flashes and fades inside 10. Winemakers running a Burgundy-style Chardonnay deliberately innoculate Oenococcus oeni after primary fermentation finishes to drop titratable acidity by a third and let diacetyl build for the buttery finish. In a biochem teaching lab, the L-malate plus NAD+ plus malate dehydrogenase reaction is the cleanest 340 nm absorbance jump a student will see all semester.
Common Uses
- Sour-candy and fruit-beverage acidulant (E296), often blended with citric for taste-time profile
- Substrate in malolactic fermentation in winemaking (L-malate -> L-lactate + CO2)
- Krebs cycle intermediate in coupled NAD+/NADH enzyme assays
- Alpha-hydroxy acid (AHA) chemical exfoliant in skincare at 1-10% concentration
- Pharmaceutical salt former and chelator (e.g., trimebutine maleate, magnesium malate)
- Plant-based meat-flavor system component (umami plus acid balance)
Safety Information
GRAS for food and supplement use. Concentrated solid and concentrated solutions can irritate eyes and broken skin (typical for any small organic diacid). 5 to 10% topical AHA formulations are well tolerated but increase UV sensitivity, so daily SPF is the standard recommendation. Oral doses up to several grams per day in supplement form are tolerated by most adults; very high intakes can produce GI cramping. Not classified hazardous under GHS at food-grade concentrations. Industrial DL-malic acid is chemically equivalent in safety profile to the L-form for food use.
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.