“Reducing sugar” is one of the lines on a calcium lignosulfonate TDS and COA that buyers most often ask about. This page explains what a reducing sugar is, where the sugars in calcium lignosulfonate come from, how they are measured, and why the value matters for concrete and other uses.
What is a reducing sugar?
A reducing sugar is a sugar that has a free aldehyde or ketone group (in its open-chain form), so it can reduce an oxidising reagent such as the copper(II) ions in Fehling’s or Benedict’s solution. All simple sugars (monosaccharides) such as glucose, xylose, mannose and galactose are reducing sugars, as are maltose and lactose. Sucrose is not, because both of its anomeric carbons are tied up in the glycosidic bond. Chemists measure reducing sugars by this reducing power, for example by copper titration (Lane–Eynon method) or by the 3,5-dinitrosalicylic acid (DNS) colour method.
Where the sugars in calcium lignosulfonate come from
Calcium lignosulfonate is recovered from the spent liquor of sulfite pulping of wood. The cooking dissolves not only lignin but also hemicellulose, so the liquor contains five-carbon sugars (pentoses such as xylose and arabinose) and six-carbon sugars (hexoses such as mannose, glucose and galactose), plus uronic acids. Part of the sugar is free and part is bound to lignin in lignin–carbohydrate complexes. Producers sell “high-sugar” and “low-sugar” grades depending on whether the sugars are removed, for example by fermentation or ultrafiltration.
In lignosulfonate analysis the reducing value also includes other reducing substances, such as loosely bound sulfur dioxide, which is why some TDS use the term “reducing matter” instead of “reducing sugar”.
Reducing sugar values on our data sheets
| Grade | Sugar | Reducing sugar / reducing matter |
|---|---|---|
| Calcium lignosulfonate Grade One (GAC-CaLS-1) | 9 – 10% | Reducing sugar around 7% |
| Calcium lignosulfonate Grade Two (GAC-CaLS-2) | 9 – 12% | Reducing sugar around 7% |
| Calcium lignosulfonate Grade Three (GAC-CaLS-3) | 10 – 12% | Reducing matter 18 – 20% |
| Sodium lignosulfonate Grade One (GAC-NaLS-1), for comparison | — | Reducing sugar 7% max |
For reference, the JECFA specification for calcium lignosulfonate (40-65) used as a food additive limits reducing sugars to 5% on the dried basis, and the EU feed-additive authorisation for lignosulphonate (Regulation (EU) 2024/749) sets a limit of 20% sugars in dry matter. Full grade data are on the calcium lignosulfonate product page.
Why the reducing sugar value matters
- Concrete and mortar: sugars retard cement hydration. A lignosulfonate water reducer with more sugar delays setting more at the same dose; overdosing can delay strength gain. See calcium lignosulfonate concrete compatibility and trial procedure.
- Oil-well cement: the same effect is used on purpose when lignosulfonate acts as a retarder; see calcium lignosulfonate for oil drilling.
- Liquids and slurries: sugars can support microbial growth during storage, so watch viscosity, odour and gas formation.
- Binders and dust control: sugars add to the tackiness of the binder, which is one reason high-sugar grades are used there.
How to compare reducing sugar between suppliers
Results from different methods are not directly comparable. Ask for the method, the basis (as supplied or dry basis) and whether the value is typical or a specification limit, then compare grades on the same basis. For a neutral background article, see reducing sugars in lignosulfonate on lignosulfonate.com.
Frequently Asked Questions
What are reducing sugars?
Sugars with a free aldehyde or ketone group that can reduce an oxidising reagent such as copper(II). Glucose, xylose, mannose, galactose, maltose and lactose are reducing sugars; sucrose is not.
How much reducing sugar is in calcium lignosulfonate?
It depends on the grade. Our Grade One and Grade Two TDS give reducing sugar around 7%; Grade Three gives reducing matter 18 – 20%.
Why does reducing sugar matter in concrete?
Sugars retard cement hydration, so a lignosulfonate with more sugar delays setting more at the same dose. Choose the grade and dose with setting-time and strength tests.
How is reducing sugar measured?
By the reducing power of the sample, for example copper titration (Lane–Eynon) or the DNS colour method. Compare suppliers only on the same method and basis.
