I have been working through McGee’s On Food and Cooking and it’s extremely great.

This stuck out:

A passage of text describing how sweet potatoes become sweeter during cooking due to an enzyme that breaks down starch into maltose. The enzyme starts working at around 135°F (57°C) and stops at about 170°F (75°C) when it denatures. Slow baking enhances sweetness by allowing more time for the enzyme to act, whereas rapid cooking methods like boiling or microwaving reduce this effect. Some sweet potato varieties can convert up to 75% of their starch into maltose, making them taste syrupy. Freshly harvested 'green' roots in autumn have lower enzyme levels

So I made a control batch of sweet potatoes for lunch (30 minutes in our baking oven) and also set up a test batch on our hob like this:

sweetpot2

I am no sort of scientist: it took me quite a long time before I realised I could stick the probe into the middle of the sweet potato to get the core temperature.

I gave them 40 minutes keeping their temp between about 60 and 72 (this is increasingly justifying why I should get an immersion circulator). Afterwards they were effectively uncooked:

Comparison of sweet pot

(The control sweet potato is on the right, the test one on the left)

I assumed the experiment has failed, so I threw them into the baking oven for 20 minutes anyway so I could eat the evidence, but when I pulled them out they were literally leaking syrup:

A fork with some cooked sugar on it

…and OMG they tasted amazing. I could easily eat them as dessert. Science!