If you’re prone to forgetting your cup right after you’ve poured it, or you’re routinely active or distracted throughout the day, you may be looking for a way to keep all of your hot beverages from turning into cold brew. Here’s our advice: Rather than reaching for the microwave or burning your tongue on too-hot coffee from a thermos, consider the humble mug warmer.
Functionally, a mug warmer is a tiny hot plate that sits on your desk and heats the bottom of your cup to keep the liquid inside hot. A good mug warmer will keep your drink warm without exacerbating unpleasant flavors via scorching. But it’s important to remember that, due to the inevitable effects of oxidation and the way these drinks break down chemically over time, there’s no way to completely preserve the body and flavor of freshly brewed coffee or tea.
“As brewed coffee sits, the perceived acidity in coffee gradually becomes higher because of the presence of quinic acid in the coffee. This effect is most commonly found when coffee is left on a heating plate for a long period of time,” said Chi Sum Ngai, founder of Coffee Project New York. “After a while, the acidity is going to shoot up. Coffee tends to be stronger in taste and not as smooth as when you first brew it.”
Tea experts we spoke with, including Bruce Richardson, owner of Elmwood Inn Fine Teas, unanimously agreed that tea loses its liveliness and turns stale the longer it sits.
All mug warmers aim to maintain a specific beverage temperature, according to what the company deems ideal for drinking; most of the warmers we researched and tested claimed to target a range between 120 °F and 155 °F (though in practice none could achieve a temperature above 145 °F). In our own testing, we found the ideal range to be between 130 °F and 140 °F. Any colder tasted lukewarm, and any hotter made sipping uncomfortable. Of course, your own preference may differ.
Since this is a category that’s rife with no-name brands and dubious marketing, we decided to test a few of the traditional mug warmers that had the best user reviews, a reasonable price point (below $50), and an attractive range of features. Our goal was simply to see whether a warmer would improve our overall drinking experience and if there was much variation among the myriad models available.
To that end, we tested each warmer by brewing a pot of coffee in our favorite cheap coffee maker, using the same settings and the same beans (specifically, Kirkland Signature House Blend medium roast). We then measured the temperature and taste of the beverages over time. Our testing for tea was identical, using both black and green tea bags from Stash.
We also called in a couple of unique, higher-end products—the Ember Mug² and the Ohom Ui Mug—to see whether they could fill a niche that a simple mug warmer didn’t.
