Maltose is made by breaking down starch with enzymes found in sprouted grain. The process is surprisingly straightforward: you cook a starchy ingredient to soften it, mix it with ground sprouted barley or wheat, hold the mixture at a warm temperature for several hours, then strain and reduce the liquid into a thick, golden syrup. The same basic chemistry powers both ancient kitchen traditions and modern syrup factories.
How Starch Becomes Maltose
Starch is a long chain of sugar molecules linked together. When you sprout a grain like barley, the seed produces enzymes called amylases that chop those chains apart. Beta-amylase is the key player for maltose production. It works from the outer ends of each starch chain inward, snipping off pairs of sugar molecules. Each pair is one molecule of maltose.
Alpha-amylase plays a supporting role. It cuts starch chains at random interior points, creating shorter fragments that beta-amylase can then attack more efficiently. Without alpha-amylase breaking the starch into smaller pieces first, beta-amylase works slowly and incompletely. Sprouted barley produces both enzymes in abundance, with roughly twelve times more amylase activity than sprouted wheat, which is why barley malt has been the go-to ingredient for centuries.
What You Need
A basic home maltose syrup requires two things: a starch source and a source of amylase enzymes. For starch, you can use sweet rice (glutinous rice), regular rice, sweet potatoes, or other starchy roots and grains. For enzymes, you need either sprouted barley, sprouted wheat, or purchased diastatic malt powder (which is just dried, ground sprouted grain that still has active enzymes).
A common starting ratio is 1 cup of your starch source to roughly 1/4 cup of sprouted grain or malt powder. Sweet rice works particularly well because its high amylopectin content breaks down easily and produces a smooth, sticky syrup.
Sprouting Your Own Grain
If you want to make everything from scratch, you can sprout barley or wheat berries at home. Soak the grains in cool water for 8 to 12 hours, then drain and spread them in a single layer on a tray or in a jar. Rinse them twice a day and keep them at a cool room temperature, ideally below 20°C (68°F). Temperatures above that encourage mold and bacterial growth.
Barley takes longer to reach peak enzyme activity than wheat. Research on grain germination found that barley germinated at around 7°C for 12 days produced the highest amylase levels, while wheat reached good activity after just five days at 20°C. For a home kitchen, sprouting at cool room temperature for 5 to 7 days until the shoots are roughly the length of the grain itself is a practical target. Once sprouted, dry the grains at a low temperature (below 50°C/122°F to preserve enzyme activity), then grind them into a coarse powder.
Step-by-Step: Making Maltose Syrup
Start by cooking your starch source. If using rice, cook it with extra water until it’s very soft and porridge-like. If using sweet potatoes, peel, chop, and boil them until completely tender, then mash them with their cooking water into a smooth slurry. The goal is to gelatinize the starch, which happens when starch granules absorb water and swell at temperatures above 60°C (140°F). This makes the starch accessible to the enzymes.
Let the cooked starch cool to about 65°C (150°F) before adding your ground sprouted grain or malt powder. This temperature matters. Beta-amylase, the enzyme that produces maltose, is most active between 55°C and 65°C (131°F to 150°F) and works best at a slightly acidic pH of around 5.0 to 5.6. If the mixture is too hot, you’ll destroy the enzymes before they do their work.
Stir in the malt thoroughly and hold the mixture at this warm temperature range for 4 to 8 hours. You can do this in a low oven, a slow cooker set to its lowest setting, a large thermos, or a pot wrapped in towels. Stir occasionally. Over these hours, the amylases will convert the starch into maltose and other simple sugars. You’ll notice the mixture becoming thinner and sweeter as the long starch chains break apart.
Once the conversion period is complete, strain the liquid through cheesecloth or a fine mesh bag, squeezing out as much sweet liquid as possible. Discard the spent grain solids.
Reducing the Liquid to Syrup
Pour the strained liquid into a wide, heavy-bottomed pot and bring it to a gentle boil. Reduce the heat and simmer, stirring frequently to prevent scorching. You’re evaporating water to concentrate the sugars into a thick syrup. This step can take 2 to 4 hours depending on how much liquid you started with and how wide your pot is.
Maltose begins to caramelize at temperatures above 120°C (248°F), so as long as you keep the syrup at a gentle simmer with water still present, you won’t reach that threshold. The risk increases only at the very end when most of the water has evaporated. Watch carefully during the last 30 minutes and reduce heat as the syrup thickens. The finished syrup should coat the back of a spoon and drip off in slow, heavy threads. It will thicken further as it cools.
The final product is a pale amber syrup with a mild, malty sweetness that’s less intense than honey or table sugar. Stored in a sealed jar, it keeps for several months at room temperature.
Why Temperature Control Is Everything
The single biggest factor in how much maltose your syrup contains is the temperature you hold during the conversion step. Beta-amylase, which produces maltose, thrives between 55°C and 65°C. Alpha-amylase, which produces a mix of shorter sugar chains (some fermentable, some not), is more active at higher temperatures. Brewers exploit this same chemistry when making beer: mashing at the lower end of the range yields more maltose and a drier, more fermentable result, while mashing at the higher end yields more complex sugars and a fuller body.
If you hold your mixture closer to 60°C (140°F), you’ll get a syrup with a higher proportion of maltose. If you let it creep up toward 70°C (158°F), alpha-amylase dominates and you’ll end up with more of a mixed-sugar syrup, still sweet but with a different character. A simple kitchen thermometer is the most useful tool in the whole process.
How Industrial Maltose Syrup Is Made
Commercial producers follow the same basic logic at a much larger scale. They start by mixing cornstarch or another purified starch into a slurry at 15% to 40% solids concentration. The starch is gelatinized with heat, then partially broken down (liquefied) using acid or industrial alpha-amylase to reach a low level of conversion. This first step creates a pourable liquid of short starch fragments.
Next comes saccharification, where a specialized beta-amylase (historically from bacteria like Bacillus polymyxa) converts those fragments into maltose. This reaction runs at 55°C to 65°C and a pH between 5.8 and 7.0 for 24 to 48 hours. The resulting liquid is then filtered, decolorized with activated carbon, passed through ion exchange resins to remove minerals and off-flavors, and finally evaporated to above 50% solids. Commercial high-maltose syrups typically contain 35% to 65% maltose on a dry basis.
The home method skips the purification steps but follows the same core sequence: gelatinize starch, add amylase, hold at the right temperature, then concentrate. Your kitchen syrup will contain maltose along with some glucose, longer sugar chains, and traces of grain flavor, which is exactly what gives traditional maltose candy and Asian malt sugar their distinctive taste.