Sugarcane Crushing, Gur & Khandsari Making

Sugarcane and its composition

India is among the world's two largest producers of sugarcane. Processing converts cane into three major products: mill (plantation white) sugar, khandsari and gur (jaggery).

• Juice extracted from cane contains about 15–20 % total soluble solids (°Brix), of which sucrose is the main part.
• Purity of juice = (sucrose ÷ °Brix) × 100. A purity above about 85 % is considered good.
• Maturity and freshness matter — sucrose is lost by inversion if cane is stored for long after harvest, so cane should be crushed within about 24 hours of cutting.

Juice extraction — crushing

Roller crushers

• Cane is passed between heavy rollers which squeeze out the juice.
• Three-roller mill is the standard unit: two feed/top rollers and one discharge roller (typically arranged in a triangle), with a trash plate to guide the crushed cane. Small power-driven mills and bullock-driven vertical three-roller crushers are commonly used for gur and khandsari.
• Parts: rollers, frame, gearbox (reduction), feeding table, juice trough, drive (electric motor, diesel engine, or bullock sweep).
• Roller surface is grooved to help grip the cane. The gap between the discharge roller and the top roller is smaller than the feed side.
• In sugar factories, multiple mills in tandem (4 to 6 mills) with maceration (spraying water or thin juice on the bagasse between mills) are used to raise extraction.
• A cane preparatory device (knives, shredder, fibrizer) ruptures the cells before milling to raise extraction.

Performance terms

• Small three-roller crushers (single pass) give about 55–65 % juice extraction; modern sugar-mill tandems with maceration give above 95 % sucrose extraction.
• Roller speed, roller pressure, setting of the gap, feed rate and cane variety affect extraction.

Juice clarification

Raw juice contains suspended and colloidal impurities (soil, waxes, proteins, gums). Clarification removes them:

1. Straining to remove coarse particles.
2. Heating the juice (to about 60–70 °C initially) to coagulate proteins.
3. Addition of clarificants — lime (milk of lime) to neutralise acidity (to pH about 7–7.2) and form flocs, and natural plant-based clarificants (such as the mucilage of bhindi (okra) stems, deola, or chemical flocculants) which bring scum to the surface.
4. Skimming the scum during boiling.

Gur (jaggery) making

Gur is an unrefined, non-centrifugal sugar made by boiling cane juice until it solidifies. It retains molasses, minerals and iron, so it is nutritionally richer than white sugar.

Process

1. Juice extraction in the crusher.
2. Straining and settling of juice.
3. Clarification in a pan using lime and a natural clarificant; scum is skimmed off repeatedly.
4. Boiling and concentration in open pans over a furnace, with juice moved from one pan to another (or a single large pan) until the final massecuite reaches the striking point at about 116–120 °C.
5. Cooling and stirring (graining) in a wooden trough or mould, and moulding into blocks (balls, cubes, or powder/granular gur).
6. Storage and packing — gur is hygroscopic; storage at low humidity is important, and moisture content in good gur is kept at about 5–8 %.

Furnace and pan

• Traditional furnaces are single-pan or multi-pan and burn bagasse (dried) as fuel; thermal efficiency is only about 15–25 %.
• Improved furnaces (developed by research institutes in several regions) use better flue design, a chimney, grate, and pans arranged so that hot gases pass in series, improving efficiency and saving bagasse.
• Pan design: shallow pans with a large heating surface, made of mild steel or galvanised iron; a series of pans gives gradual concentration.

Quality and yield

• Yield of gur is about 10–12 % of cane weight; higher in good cane with efficient clarification.
• Good gur is light golden-brown, hard, and non-sticky; it should have low reducing sugar. Poor gur is dark, sticky and breaks.
• Lime in excess causes darkening; improper clarification causes poor colour and storability.