Sugarcane juice is sold from carts with a press running continuously rather than from a jug. The reason is that the juice is unstable from the moment it is extracted.
Enzymes act as soon as the cell walls break
Crushing releases enzymes that were compartmentalized in the intact stalk, and they immediately begin reacting with compounds in the juice.
One visible result is browning, as phenolic compounds oxidize in the presence of air, the same reaction that darkens a cut apple.
The pale green juice turns dull and grayish within a short time, and the flavor shifts alongside the color rather than lagging behind it.
The sugar concentration invites microbial growth
Fresh cane juice is a dilute sugar solution at ambient temperature, which is close to an ideal growth medium for yeasts and bacteria.
Fermentation begins quickly in warm conditions, producing a sour, slightly fizzy character that is unmistakable once it has started.
This is why the drink is associated with hot climates and short supply chains, since the same conditions that create demand also shorten the window.
Additions do more than flavor
Vendors press lime and sometimes ginger into the juice as it runs, and the acid slows the browning reaction as well as balancing the sweetness.
Lime also masks the flatness that develops as the juice sits, which is part of why the combination became standard rather than optional.
Ice does the rest, lowering the temperature enough to slow both the enzymes and the microbes for the few minutes the drink exists.
Packaging it requires stopping the reactions
Bottled cane juice exists, but it has to be heat-treated or otherwise processed, which alters the fresh, grassy character that makes the drink distinctive.
Freezing is the alternative, and frozen juice keeps more of the original flavor, which is how the product reaches markets far from where cane grows.
Neither route reproduces the cart, since part of what a fresh press delivers is a temperature and an aroma that exist only in the minute after crushing.
Safety follows from handling, not the juice
Because it is unpasteurized and served cold, cane juice sits in the same category as other fresh-pressed drinks, where the equipment and the water used for ice matter.
Food safety agencies publish guidance on unpasteurized juices, including advice for groups at higher risk, and that guidance is the right reference rather than local custom.
The practical signal at a cart is the same one that applies to any fresh press, which is a machine that is visibly clean and a queue long enough to keep it running.