Perfecting potato puree
In the realm of all things spudular, French fries are king, but mashed potatoes are a close second. As with fries, there are certain criteria that can be used to distinguish good examples of the genre from bad. Mashed potatoes, however, come in two acceptable styles, like peanut butter: chunky and smooth. Chunky mashed potatoes (which I call “British mash”) are easy to make: peel potatoes, cut them into large pieces, boil them until tender, then mash with a masher, adding butter, milk and salt to taste.
Smooth mashed potatoes (a.k.a. “potato puree”) are a different story entirely. They need to be handled carefully, lest they turn into a gluey mess. The starch in potatoes is contained in granules; if the potatoes are overcooked or overworked, those granules will break, the starch will leak everywhere, and the puree will get very sticky. (This isn’t as big a problem with chunky mash, since the risk of overworking the potatoes is less when you’re not trying to eliminate every last chunk.)
Fortunately, there is a known fix for this problem: by heating the potatoes precisely to their gelation (or gelatinization) temperature, holding them there, and then chilling them down again, you can retrograde the starch, which stabilizes it and prevents it from leaking out of the granules. This technique is often credited to Jeffrey Steingarten, who described it in his book The Man Who Ate Everything, and is now widely used. (You may recall that I’ve mentioned starch retrogradation before.)
To put this theory into practice, I cobbled together an approach based on notes from eGullet. Because it requires holding the potatoes at a constant temperature over a period of time, it’s a process that is perfectly suited to an immersion circulator, so I started by putting the peeled-and-sliced potatoes into a vacuum bag along with their skins (for added flavour) and some water. I cooked them at 70°C for 45 minutes, then chilled them in ice water and put them in the fridge. Later, I drained them (keeping the starchy water), discarded the peels, and boiled the potatoes until they were softened. I passed them through a food mill fitted with the fine disc, then heated the resulting puree, adding butter and adjusting the texture with the reserved starchy water.
The final product was not the perfect potato puree I was looking for: there was a detectable grittiness to it that could be compared to polenta, which I suspect came from incompletely gelating the starch, or possibly from not chilling it sufficiently. Either way, the fault was in the execution, not the theory. And it was fascinating to be able to work the puree as much as I wanted without it ever getting noticeably sticky.
Which do you prefer: chunky mashed potatoes or smooth potato puree?