Bagasse

The cane stalk is a composite: long structural fibres running lengthwise, and a soft parenchyma pith between them that holds most of the juice. Crushing tears the structure open to release the juice, so bagasse contains both — mixed, shredded, and still wet, since no mill extracts every drop and no mill dries the residue before burning it.

The fibre-and-pith distinction is the key to bagasse’s non-fuel uses. Pith is short, absorbent, and useless for making paper, while the long fibres are genuinely valuable pulp material. Any process making paper or board from bagasse therefore starts with depithing — separating the two — and the pith it rejects goes back to the boiler. Burning, by contrast, takes both without complaint, which is one reason burning wins so often.

The arithmetic of a cane mill is neat: the crop delivers both the sugar and the fuel needed to extract it, at the same time and to the same place. Bagasse is fed straight from the crushing train to the boilers, raising steam that drives the mill and heats the evaporators and pans, with the exhaust and turbine stages generating electricity. During the crushing season, a well-run factory buys little or no outside energy.

Where boilers are efficient enough, a mill produces surplus bagasse and surplus power. Cogeneration for export to the grid has become a substantial second business for cane industries in several countries, and it changes the economics of the residue: bagasse that once had to be got rid of now has an opportunity cost, and mills weigh burning it against selling it or converting it. Research and commercial interest in cellulosic ethanol from bagasse rests on the same fact — a large, already-collected, already-shredded stream of lignocellulose sitting in one place.

Beyond the boiler, bagasse pulp goes into paper and board where wood is scarce, and into particleboard and fibreboard. Moulded bagasse tableware and packaging have grown as substitutes for plastics. It is also used as animal feed, though its value there is modest, and as a mushroom substrate and a soil amendment. None of these compete with fuel use at scale in most industries, because the mill’s own energy demand generally comes first.

Storing bagasse is genuinely awkward. It arrives wet, it is bulky and low in density, and a pile of it is biologically active: it composts, it heats, and heaps have been known to reach ignition, so bagasse yards are laid out and managed with fire in mind. It also degrades in storage, losing fibre quality for pulping. Mills that must hold bagasse over a shutdown bale or compact it and manage the stack deliberately; most simply arrange to burn it as it comes.