From field to crystal

Growing and Harvesting

Sugarcane is a tropical grass that grows 3 to 4 metres tall over 12 to 18 months. Zimbabwe's Lowveld, in the Chiredzi District of Masvingo Province, provides ideal growing conditions: warm sun, fertile soil, and established irrigation infrastructure. The region sits at an elevation of 150 to 600 metres above sea level.

Zimbabwe's estates achieve remarkable yields of approximately 100 tonnes per hectare, significantly above the African continental average of 63 tonnes per hectare. Cane is sourced from estate-owned plantations (Hippo Valley farms approximately 12,000 hectares, Triangle around 14,000 hectares) and from private outgrower farmers, including small-scale farmers on the Mkwasine Estates (around 8,200 hectares).

Cane is transported to the mills by truck, narrow-gauge railway, and trailers. Timing is critical: sucrose content drops rapidly after cutting, so minimising the field-to-mill time is essential for high sugar recovery.

Crushing and Juice Extraction

At the mill, the cane first passes through rotating knives and shredders that break open the plant cells. The prepared cane then moves through a train of four to six heavy roller mills. Each set of rollers crushes the cane under enormous pressure, squeezing out the sugar-rich juice.

Hot water is added at the last mill and flows backwards (counter-current) through the milling train, dissolving and carrying away more sugar at each stage. This process, called imbibition, increases extraction efficiency by 2 to 5 percentage points. Modern mills extract 95 to 98% of the available sucrose. The fibrous residue left behind is called bagasse.

The Hippo Valley and Triangle mills have a combined crushing capacity of over 4.8 million tonnes of cane per year. They operate 24/7 during the milling season.

Clarification

The raw juice is dark and cloudy, containing soil particles, plant fibre, and other impurities. Clarification cleans it up. Lime (calcium oxide) is added to the juice, which is then heated. The lime reacts with impurities, forming a heavy sludge called mudcake that settles to the bottom.

The clear, golden juice is drawn off the top and sent forward for concentration. The mudcake, rich in calcium and organic matter, is returned to the cane fields as fertiliser, closing the nutrient loop.

Evaporation

The clarified juice is still about 85% water. Multiple-effect evaporators boil off this water efficiently by using steam at progressively lower pressures across a series of connected vessels. Each vessel reuses the steam generated by the previous one, saving enormous amounts of energy.

By the end of evaporation, the juice has been concentrated from about 15% sugar content to approximately 65%. The resulting thick, golden liquid is called syrup.

Crystallisation

The syrup enters large vacuum pans where sugar crystals are grown under carefully controlled conditions. A small amount of fine sugar dust or seed crystals is introduced, and the syrup is concentrated further under vacuum (which lowers the boiling point and prevents caramelisation).

Crystals grow slowly over several hours as more syrup is added. The skill of the pan operator lies in growing uniform crystals of the right size. The resulting mixture of crystals suspended in syrup is called massecuite.

Centrifuging, Drying, and Packaging

The massecuite is spun in high-speed centrifuges (essentially large spinning baskets) that separate the sugar crystals from the remaining syrup (molasses). The crystals are washed with a small amount of hot water during spinning.

The separated raw sugar is dried with warm air to reduce moisture content, then graded and either packaged for sale as raw or brown sugar, or sent to a refinery for further processing into white sugar. Zimbabwe has two standalone refineries operated by StarAfrica Corporation in Harare and Bulawayo, with a combined refining capacity of 260,000 tonnes. The refining process involves re-dissolving the raw sugar, removing colour through activated carbon, re-crystallising, and drying to produce white sugar.