The Food Lab: Better Home Cooking Through Science

strengthens the pectin with the aid of a natural enzyme
called pectin methylesterase (PME). According to an article
in the Journal of Agricultural and Food Chemistry, PME
induces calcium and magnesium to act as a sort of buttress
for the pectin. They strengthen the pectin’s hold on the
potato cell’s walls, which helps the potatoes stay firmer and
more intact even as their starch granules swell and burst.
Like most enzymes, PME is only active within a certain
temperature range, acting faster and faster as the
temperature gets higher and higher until, like a switch, it
shuts off completely once it reaches a certain level.
Think of PME as little factory workers hard at work
building cars. As their floor manager, if you apply a bit of
pressure to them (in the form of heat), at first that will get
them to work faster. Cars will come off the production line
at a faster clip. But apply too much pressure (by
overheating), and the little enzymes just won’t be able to
take it any more, throwing down their tools and walking out.
Production slows to a halt. For PME, that shut-off point is
just slightly above 170°F.
Unfortunately, most home cooks don’t have an easy way
to maintain a water bath at exactly 170°F for the requisite 15
minutes. I needed to find an alternate way to maintain the
pectin structure of the potato while still releasing the starch
molecules, and it struck me: it’s as easy as apple pie.
What’s apple pie got to do with French fries? Well,
anyone who’s ever baked an apple pie knows that different
apples cook differently. Some retain their shape, others turn
to mush. The difference largely has to do with their acidity.
Thus, supertart apples like Granny Smith will stay fully