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.