Maltose
Properties
| State | Solid (white crystalline powder) |
| Color | White |
| Solubility | Soluble in water; slightly soluble in ethanol |
| Melting Point | 102-103 °C (monohydrate) |
| Boiling Point | Decomposes before boiling |
About Maltose
Maltose is two D-glucose units linked head-to-tail by an alpha-1,4 glycosidic bond, leaving the C1 anomeric hydroxyl on the second glucose free to mutarotate between alpha and beta forms. That free anomeric center is what makes maltose a reducing sugar (it gives a positive Benedict's and Fehling's test, and a positive 3,5-dinitrosalicylic acid assay), in contrast to sucrose, where both anomeric carbons are tied up in the alpha-1,beta-2 linkage between glucose and fructose. The disaccharide is the signature product of starch hydrolysis: when barley grains are steeped, germinated, and kilned in the malting process for brewing, the seed's own alpha- and beta-amylases cleave amylose and amylopectin from the inside and the non-reducing ends respectively, releasing maltose and small dextrins. The mash step of brewing — barley grist held at 62 to 68 °C for an hour with water — is essentially a controlled maltose-extraction operation, and the wort that gravity-feeds into the kettle is mostly maltose that yeast will subsequently ferment to ethanol via maltose permease and the alpha-glucosidase MAL62. In human digestion the same chemistry happens inside us: salivary alpha-amylase starts the job, pancreatic alpha-amylase finishes the bulk hydrolysis to maltose and the alpha-1,6-branched limit dextrins, and the brush-border maltase-glucoamylase complex on small-intestinal enterocytes takes maltose down to two glucose monomers for SGLT1-mediated absorption. Sweetness is roughly 30 to 60 percent of sucrose, so corn-syrup blends high in maltose are popular when calories and texture matter more than headline sweetness — pretzels, malt vinegar, and the brown crackle on Chinese roast duck all owe their flavor and surface chemistry to maltose Maillard chemistry.
Where you'll encounter it
If you have ever brewed a beer from grain instead of extract, watched a Chinese chef brush maltose syrup over a Peking duck before roasting, or run a DNS reducing-sugar assay on saccharifying enzyme broth, you have been working with maltose. A brewer holding the mash at 65 °C for an hour is running barley's own beta-amylase at its temperature optimum to maximize maltose yield from amylose and amylopectin — drop to 62 and you favor more fermentable wort, push to 68 and you leave more dextrins behind for body. A Peking duck cook brushes a thin maltose-water syrup over the air-dried skin so that during roasting the disaccharide caramelizes and Maillard-reacts with the surface protein to produce the mahogany lacquer crust. Enzyme assay benches running the 3,5-DNS protocol read maltose-equivalents at 540 nm to quantify alpha-amylase activity in industrial saccharifying broths.
Common Uses
- Primary fermentable sugar in barley wort for beer brewing and Scotch whisky distilling
- Brown-glaze ingredient brushed on Peking duck and Cantonese char siu
- Malt-syrup sweetener in bagels, pretzels, and rye breads
- Carbon source in bacteriology media (e.g., MacConkey-maltose for Gram-negative differentiation)
- Reference reducing sugar for Benedict, Fehling, and DNS assays
- Substrate for assaying alpha-glucosidase and acarbose IC50 in diabetes drug discovery
- Standard in HPAEC-PAD oligosaccharide separations
Safety Information
GRAS for food use. Non-toxic at any culinary concentration. Patients with congenital sucrase-isomaltase deficiency or generic alpha-glucosidase deficiency may experience osmotic diarrhea from large maltose loads because they cannot hydrolyze it to absorbable glucose. Diabetics should treat maltose like glucose for glycemic-load purposes — once hydrolyzed it raises blood glucose just as quickly. Not classified under GHS.
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.