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DELICIOUS meals don’t get much simpler than a baked sweet potato. But a little science can tell us how to maximise this dish’s sweetness and deepen its flavour.

Sweet potatoes are between 1 and 2.5 per cent sugar when raw, but they get sweeter as they cook thanks to the work of amylase enzymes that break down starch into simple sugars. These enzymes are .

found that the sugar content of one type of sweet potato was almost five times higher after baking for 90 minutes, mainly due to an increase in maltose. A fragrant aroma and soft texture are also important to the experience, and the cooking method has a big effect here. Another study analysed the aroma compounds produced by baking, boiling and microwaving sweet potatoes. , boiling resulted in only 54 per cent of the aroma molecules from baking and microwaving generated just 6 per cent.

Many of the aroma molecules in baked sweet potatoes are products of sugar caramelisation and the Maillard reaction, which occurs when sugars and amino acids are heated above 100°C (210°F) and creates the characteristic flavour of roasted and toasted foods. When sweet potatoes are boiled, the temperature doesn’t get above 100°C, so this flavour development doesn’t happen. The breakdown of starch into simple sugars during baking also helps by creating more substrates for these reactions, leading to a more fragrant and flavoursome result.

One advantage of baking is that heat diffuses from the outside to the inside of the tuber relatively slowly, so the flesh spends plenty of time in the temperature range where amylase enzymes are most active. When sweet potatoes are microwaved, they heat up faster and the amylase enzymes are quickly inactivated by the high temperature, .

the effects of roasting for different lengths of time at 220°C (430°F), and found that anything from 1 to 2 hours of cooking was well liked by volunteers.

Inspired by chef Lucas Sin, explains how a surprising trick takes baked sweet potatoes to another level: freezing before baking. This seems to be because freezing ruptures plant cell walls. When the frozen tubers go into the oven, more water escapes from the flesh, concentrating the flavour, and sugary fluid caramelises on the outside.

To maximise amylase activity, Chin suggests baking sweet potatoes at 150°C (300°F) for 2 hours, before increasing the heat to 230°C (450°F) for 40 minutes. This might not appeal when we are all conscious of our energy usage, but in my tests, frozen sweet potatoes turned out great after baking for 1 hour at 200°C (390°F).

Sam Wong is assistant news editor and self-appointed chief gourmand at Â鶹´«Ã½. Follow him @samwong1