How Maltitol Is Made: Hydrogenation of Maltose Explained

Maltitol is what you get when hydrogen is added across the carbonyl group of maltose, a sugar built from two glucose units. The chemistry is simple to describe; the industrial process is a carefully sequenced chain of enzymatic, separation and catalytic steps that decides whether the output is a clean, free-flowing crystal or a consistent syrup. Understanding those steps lets buyers ask sharper questions about purity, crystal form and the consistency of each batch.

From Starch to High-Maltose Syrup

The route starts with starch, most often from corn but also from wheat, tapioca or potato. In liquefaction, heat and an alpha-amylase enzyme thin the starch paste into shorter chains. Saccharification then uses enzymes such as glucoamylase or a maltose-forming amylase to convert those chains into sugars, with the goal of a syrup rich in maltose. The enzyme choice, dose, temperature, pH and time determine the sugar profile. A high maltose content is valuable because maltose is the precursor that becomes maltitol, so a more selective saccharification reduces the load of other sugars that would turn into different polyols.

Purification Before Hydrogenation

Raw hydrolysed syrup carries protein, colour bodies, salts and fine solids that would poison the catalyst or contaminate the final product. Producers clarify it by filtration and often treat it with activated carbon to remove colour, then pass it through ion-exchange resins to demineralise and further purify the stream. Some plants add a chromatographic separation step to raise the maltose fraction even higher. This is also where reducing sugars are brought under control, since an excess of them can darken the product and complicate the reaction downstream.

The Hydrogenation Reactor

In the core reaction, the purified syrup meets hydrogen gas in a pressurised reactor over a metal catalyst, commonly Raney nickel. Under controlled temperature and hydrogen pressure, the aldehyde group at the end of each maltose molecule is reduced to an alcohol, converting maltose into maltitol. Any glucose present becomes sorbitol, and larger saccharides become their corresponding polyols, so the final profile always reflects the incoming sugar spectrum. Reaction conditions are tuned for conversion and selectivity: enough severity to finish the job, but not so much that side products, colour or degradation compounds increase.

Catalyst Removal and Refining

After the reaction, the catalyst is filtered out and often recovered for reuse. Residual nickel is a key safety parameter, and food-grade maltitol is expected to sit well below the strict residue limits set by regulators. The liquor then passes through ion exchange and carbon treatment again to remove dissolved metals, salts and colour, followed by concentration under vacuum. Deodorising and polishing steps may follow to deliver a clean, neutral-tasting solution.

Crystallisation, Milling or Syrup

From the refined liquor, the process splits into two destinations. To make powder, the concentrated solution is crystallised under controlled cooling and seeding, then the crystals are separated by centrifuge, dried, milled and sieved to a target particle size. The crystallisation conditions also influence which polymorph forms, and the stable beta crystal is the grade most often specified for chocolate and coatings. To make syrup, the refined liquor is simply adjusted to the required solids, typically around 75 percent or more, and filled hot into drums or totes. Both streams are packed under controlled humidity so that moisture does not compromise quality.

What Buyers Should Verify

The certificate of analysis is the entry point, not the whole story. For powder, confirm maltitol content, water, reducing sugars, pH, ash, heavy metals and nickel residue, plus the crystal form and particle-size distribution. For syrup, confirm the solids range alongside the same chemical limits, and check how solids are measured. It is also worth asking whether the product is made in-house or toll-processed, and how the producer handles lots that fall slightly outside specification. A traceable batch record, retained samples and consistent certificates turn a good conversation into a reliable supply arrangement.

Frequently Asked Questions