The perfect bagel is a mix of soft and chewy. It's heavenly on day one. It's acceptable to eat on day two. But by day three, you may break a tooth trying to eat it for breakfast. When bread dehydrates, it becomes stale. Fortunately, there are several tricks that you can employ to soften a hard bagel.
Put your stale bagel on a microwave-safe plate and brush a small amount of warm water over the top of the bagel. Then wrap the bagel in a paper towel and microwave it for 10 to 20 seconds, or until soft to the touch. The water will regelatinize the starches in the bagel and it will be easier to chew.
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The last bagel in the bag can, indeed, be revived. Wrap the bagel in a damp paper towel, then wrap that completely in foil and pop it into the oven at 350 degrees Fahrenheit for 20 minutes. The steam will soften the bagel. If you have access to an electric steamer, you can use that, as it will soften the bagel in the same way.
Depending on the toughness of the stale bagel, you can dip it in soup or spread it with garlic butter. Try spreading it with butter, toasting it, and then putting it directly into the soup in chunks. The liquid will soften the bread.
Look Before You Eat
If a bagel looks white, green or fuzzy, do not eat it. These features could indicate mold, microscopic fungi that can result in a serious allergic reaction or even food poisoning. Mold can develop anywhere from several days after purchasing bagels to several weeks, depending on the level of preservatives in the bread products. Always check your bread products for mold before eating, as mold can appear either on the surface or below the surface of food products. Steaming, microwaving or otherwise repurposing stale bagels does not remove mold -- and you can't just cut off the moldy portions, as mold on the surface means mold has spread throughout the bagel.