Chinese Maltose Glazes (Peking Duck & Char Siu)

What it is

Lacquering glazes built on maltose (maiyatang, 麦芽糖), a thick malt-sugar syrup, used to give Peking duck its crisp mahogany skin and char siu (Cantonese roast pork) its glossy red-brown surface. Maltose is a disaccharide of two glucose units, distinguishing it chemically from sucrose (glucose + fructose) and honey (mostly fructose and glucose).

The science

The heart of this entry is why maltose specifically. Maltose is a reducing sugar (both glucose units can drive Maillard browning), but its glucose-glucose structure browns controllably and evenly into a deep mahogany, where the fructose that dominates honey caramelizes and Maillard-browns at a lower temperature and far faster — meaning honey scorches and goes blotchy and bitter on a roasting duck. Maltose is also less sweet than sucrose or fructose, so it delivers color and gloss without cloying a savory roast. It is intensely viscous and sticky, forming an even, adhesive lacquer that tightens onto the skin. And it is less hygroscopic than honey or fructose, so it lets the skin dry tight and crisp rather than drawing moisture and softening — which is exactly why a Peking duck, coated in maltose solution and air-dried for hours or overnight, roasts to that shattering crackle. (Honey is sometimes added at the end of char siu for extra gloss and sweetness, but maltose remains the workhorse for even browning and the sticky base lacquer.)

How it's made

Peking duck (a craft, summarized): the skin is loosened from the flesh, the bird scalded, then coated in a maltose-water solution (sometimes with vinegar), hung to air-dry 8–24 hours, and roasted until the lacquer browns and the skin crisps. Char siu: pork (shoulder or butt) is marinated overnight in maltose, soy, hoisin, fermented bean curd, five-spice, and often red yeast rice or coloring, then roasted hung or on a rack, basted with warmed maltose and reserved marinade, and finished with a honey-maltose glaze and a quick high-heat char at the edges. Because maltose is rock-hard at room temperature, it must be warmed in a water bath to flow.

Regional variations

Peking duck is an imperial dish of Ming- and Qing-era Beijing, immortalized by houses like Bianyifang (closed-oven method) and Quanjude (1864, hung-oven method). Char siu (叉燒, "fork-roast") belongs to the Cantonese siu mei roast-meat tradition of Guangdong and Hong Kong. Maltose itself is ancient in China, long used in traditional sweets like malt candy and dragon's-beard candy.

Cultural & historical context

Maltose predates the wide spread of cane sugar in China; it is produced by using grain malt (barley or rice) to enzymatically convert starch into maltose, tying these glazes to a deep agrarian, grain-based sweetening tradition rather than to cane.

Reference notes

Cross-link char siu ↔ Peking duck, the maltose vs. honey vs. sucrose browning page, the Maillard reaction, teriyaki and mitarashi (soy-sugar glaze cousins), hoisin, and five-spice and red yeast rice. Pairs with steamed buns, pancakes, scallion, and cucumber.

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When to use

Reach for maltose whenever you want an even mahogany lacquer, crisp skin, controlled browning, and restrained sweetness — the defining needs of savory roast meats. Choose it over honey precisely where honey would burn, oversweeten, or soften the skin.

What goes wrong

Uneven or burnt color from too much sugar, too high heat, or substituting honey for maltose. Soft, un-crisp duck skin from insufficient drying, excess moisture, or a hygroscopic sugar. Maltose too stiff to spread — warm it to flowing. A pale glaze from too few coats or inadequate drying time.