Recipes engineered for perfection—what exactly does that mean? We take you inside Cook’s Illustrated’s science experiments.
We normally store sweet potatoes away from the light at a cool room temperature. But we couldn’t help wondering if that was really the best way. We set out to see if storing them in the refrigerator would make them last longer, or if it would do more harm than good.
We bought a case of sweet potatoes and divided it into two batches. We kept each batch for four weeks, one at room temperature (in a cabinet, between 55 and 65 degrees) and one in the refrigerator (between 34 and 38 degrees). When the time was up, we took the potatoes out of the refrigerator, allowed them to come to room temperature, then cut up both batches and roasted them in a 400-degree oven for 45 minutes. We tasted them blindly to see if we could tell the difference between the refrigerated and non-refrigerated potatoes.
While the room temperature potatoes were creamy and soft all the way through, the refrigerated ones remained hard at the center. To see if another cooking method would produce different results, we repeated the test, this time slicing both batches and boiling them for 40 minutes. The outcome was the same: the refrigerated potatoes had tough centers.
Why does refrigerating sweet potatoes make them tough? It turns out that the vegetable contains an enzyme called demethylase. The enzyme normally lies dormant, but if the potato is subjected to temperatures below 55 degrees for a prolonged period, it kicks into gear. The enzyme then weakens the pectin that holds the potatoes’ cells together, causing the pectin to bind with the calcium ions that are also present. The calcium ends up strengthening the cells’ walls so that they can’t be broken down—even by prolonged cooking.
The bottom line? If you keep your sweet potatoes in the fridge, it’ll be a tough situation to recover from. For the best possible spuds, keep them in a cool, dark place.
MAKE IT NOW: Our recipe for Roasted Sweet Potatoes is free through February 28, 2013.