With the exception of perhaps Twinkies and honey, every food in the world has a half-life. A rate at which it decays toward a slow, asymptotic, petrified or putrefied death. Sometime before it reaches that state of dryness or rot, it passes the W.E. barrier: the point at which it is no longer Worth Eating. For bagels, in particular, that line is close to zero. A good bagel will lose most of its desirable eating qualities within an hour or so of coming out of the oven, and become entirely inedible less than a day later.
But do not despair! For there are ways of casting a lifeline out to bagels that are on the brink of falling over the W.E. barrier. The question is: Which method is the best?
Let's get one thing straight right off the bat. As a bagel sits in your kitchen over the course of a day or two, two distinct processes are going on: dehydrating and staling. In order to rescue an old bagel, you need to address both.
Dehydrating is the process of losing moisture. It happens as free water inside your bagel slowly finds its way to the surface and leaps off into the atmosphere, never to return. In the open, this happens pretty fast, but you can mitigate it by storing bagels in a plastic bag to prevent excess moisture loss. This will, of course, soften up the crust, but we'll deal with that later.
Staling is the retrogradation of gelatinized starch into a rigid crystalline structure. In other words, when bread is fresh, its starch is fluid. It moves around as you prod and stretch and tear at the bagel or the loaf. But as bread rests, those starch molecules eventually align themselves into a more rigid form, making the bread firm and tough, even if it hasn't lost any moisture at all. Minor staling can be reversed by applying a bit of heat and getting those starch molecules fluid again.
At first, I tried running my experiments with a dozen or so bagels from Beauty's, a Montreal-style shop in Oakland that makes some of the finest bagels in the country. However, I quickly discovered that Montreal-style bagels, with their thinner figure and denser crumb, are not representative of the standard bagel, and that for a true test, I'd need to get my hands on some honest-to-goodness New York bagels.
That, or maybe I just needed an excuse to have some good New York bagels overnighted to me.
I made a quick call back to Serious Eats World Headquarters in New York and asked Ed Levine to pick up a half dozen mixed bagels from Absolute near his apartment on the Upper West Side and send them to me. One night and $78 later, I had them in my hand, ready for testing. For the next couple of days, I reheated those bagels, as well as the bagels from Beauty's, using a half dozen different methods, ranging from the microwave to the toaster to the broiler to the oven to a skillet. Here are the most effective methods.
Storing your bagel properly is the first step toward ensuring that it'll reheat. I generally leave most hearty breads in a paper bag or a bread box at room temperature, as the refrigerator can actually hasten staling. A bagel, on the other hand, I actually prefer to keep in the fridge, because we'll be taking steps to fix staling issues down the line. I store my bagels in a sealed zipper-lock bag in the refrigerator.
For longer-term storage, the freezer is your friend. Wrap individual bagels tightly in aluminum foil (it's more airtight than plastic wrap) and freeze them for up to a month or so. Any longer, and you'll run the risk of freezer burn. Let frozen bagels defrost in their foil packages, at room temperature, for a few hours before toasting.
If You're a Toasted-Bagel Lover: The Slice-Then-Toast
The Method: Easy. Just slice your stale bagel in half and toast it as you would a fresh bagel.
The Advantages: Your bagel comes out very much like a standard toasted bagel.
The Disadvantages: Your bagel comes out very much like a standard toasted bagel, which is to say, suboptimal.
I strongly believe that the very best bagels should not be toasted, as toasting removes the exciting contrast between the thin, crackly exterior and the chewy, dense center. You can read more about my theory in my Good Bagel Manifesto; I have a lot to say on the matter. A fresh bagel should never be toasted, but slicing-then-toasting is not a bad option for a day-old bagel that needs resuscitating.
But we can do better.
For Stale, but Not Dry Bagels: The Whole-Bagel Toast
The Method: Place the entire intact bagel into the toaster oven, or a regular oven preheated to 375°F, for four to five minutes.
The Advantages: So long as your bagel has been stored in an airtight container (a zipper-lock bag in the fridge works fine) and has been stored for no more than about three days, this will very nicely reverse the staling process, delivering a bagel with the same crisp crust and chewy interior you'd expect straight from the bagel shop. It works equally well for frozen-then-thawed bagels.
The Disadvantages: It won't work for bagels that have dried out due to improper storage.
For Stale and Dry Bagels: The Dip-and-Heat
The Method: Dip your bagel in hot water, then toast it whole.
The Advantages: I have a theory that the best way to reheat the vast majority of foods is to emulate the process by which they were cooked to begin with. Got a cold steak? Sear it in a pan again. Cold pizza? Toss it on a preheated stone (or on a preheated skillet, if you're impatient).
Bagels are cooked by first boiling, then baking, so this reheating method—which I first heard about on Dan Pashman's awesome podcast, The Sporkful, and which he subsequently detailed in his book, Eat More Better—was especially promising. Dan instructs you to run your bagel under hot water for 30 seconds before placing it in an oven or toaster oven to reheat. We're in a drought here in California, so instead of using running water, I did the socially responsible thing and instead dunked my bagels in bowls of water. I tried the method with both hot and tepid water, comparing the results side by side with a bagel that had been toasted whole without dipping.
There's no doubt that the water-dip method is effective at re-moistening a dried-out bagel. As the bagel toasts, that water evaporates, and the steam works its way up through the bagels' interiors. The water-dipped bagels were noticeably moister and steamier as I cut them in half. Heating the water seemed to make a difference, too—the bagel dipped in hot water came out just a bit crisper on the exterior, most likely due to the fact that the water got a head start on evaporating.
The Disadvantages: The one downside? The exterior just isn't quite as crisp as what you get when you toast a bagel un-dunked. That's why I recommend reserving this method only for bagels that have been stored in such a way that their moisture is not retained, such as in a paper bag on your counter.