Brown sugar turning into a compact block is the classic cupboard mischief, a highly verifiable case especially in the case in which you decide to store the sugar in a perpetually open bag, a condition in which the humidity evaporates and the crystals weld together and which will result in a boulder to be scratched with a knife. For some time, to remedy this situation, an unusual solution has been circulating on the web, which involves inserting a couple of marshmallows into the jar.
Why it works (or should work)
The mechanism, in theory, is very simple. Brown sugar remains soft thanks to molasses, which retains moisture; when this evaporates, the product hardens. The marshmallow, composed largely of water, sugar, glucose syrup and gelatin, acts as a small reservoir of moisture, slowly releasing its water into the sealed container, water that is reabsorbed by the sugar crystals. It is the same principle, explain several American sites specializing in food hacks, that lies behind the oldest trick of the slice of bread in the pantry, with the difference that the marshmallow, according to those who use it, does not go mouldy.
The advice is to place one or two marshmallows on top of the sugar, close the container hermetically and wait. This is not an instantaneous operation that is always the same, given that some talk about one night, some about an entire day, not to mention the possibility (according to a CakeWhiz guide) of using seven/eight marshmallows together to speed up the process.
What the tests say (not just anecdotes)
Most of the testimonials online are enthusiastic, and there are those who swear that the sugar remains soft for weeks, if not indefinitely, simply by leaving the marshmallows in the jar. The point is that when someone put it to the test with a stopwatch in hand, the results were more lukewarm. The American magazine Parade tested eight different methods for softening hardened sugar, and that of marshmallow was among the most disappointing: after forty minutes no appreciable change, and after twenty-four hours the largest lumps were still hard, even if the loose sugar had recovered a minimum of softness. Score awarded: 3 out of 10.
Even a guide signed by a food preservation expert for the Domino website confirms that the method works, although warning that the process is slow and needs a few days before seeing an appreciable result.
A more reliable alternative
In short, those in a hurry would do better to focus on other methods: a few seconds in the microwave with a damp cloth on top, or the oven at a low temperature, remain the quickest solutions for an already hardened block. The marshmallow, if anything, seems more effective as a prevention than as an emergency cure: keep one in the jar while the sugar is still soft, to slow down its hardening in the following months, rather than hoping for an overnight miracle capable of scratching an already formed brick.
