If you enjoy hot coffee to start the day, you know the right mug can make all the difference. But can you put hot coffee in glass? Or could that crack it?
I usually have one or two coffees each morning to get me going. And I have a favorite mug or two that just seem to make the coffee taste better.
But every so often they’re in the dishwasher at the same time, which got me wondering whether I could safely use a glass instead.
The short answer is that it is safe to put hot coffee in a glass. But the right type of glass made from certain materials is key to helping to prevent cracks or breaks.
In this article, I’ll walk through which kinds of glasses are safe to use with your hot coffee, and which you should avoid.
- How does hot coffee affect glass?
- Isn’t Pyrex made of glass? Why doesn’t that crack in heat?
- Double-walled coffee glasses
- Tips for safely using double-walled glasses with hot coffee
- Can you use a mason jar for hot coffee?
- Why are coffee mugs commonly made from ceramic?
- Can you use a glass with iced coffee?
- Can you heat up iced coffee?
- Bottom line
- More coffee answers
How does hot coffee affect glass?
The conventional wisdom is that hot liquids, coffee or otherwise, should not be used with glass as they can cause breaks or other damage. And for the most part, that’s true.
That’s because it can result in something called thermal shock. It happens when very hot liquids come into contact with cold glass (or conversely, when cold liquids are poured into a hot glass cup).
Because glass doesn’t conduct thermal energy well, if you add something like hot coffee, the sudden change in temperature can cause the glass to expand too quickly. And it may shatter. This is particularly dangerous if the glass container itself is thin.
Hot liquids can also make the exterior of the glass very hot, which could pose a burn risk if you pick it up.
Isn’t Pyrex made of glass? Why doesn’t that crack in heat?
If you do a lot of baking, you likely have some Pyrex baking dishes or measuring cups that do just fine in very hot ovens or with hot liquids. That’s because they’ve been specially designed to resist heat.
The glass used to make Pyrex is called borosilicate glass, as it includes boron. That helps reduce the ability of the glass to expand when exposed to heat.
But Pyrex is typically very thick as well. And you don’t exactly want to sip your coffee out of a thick, heavy Pyrex mug.
But you have another option if you prefer to use a glass instead of a mug for coffee: double-walled glasses.
Double-walled coffee glasses
You may have a water bottle that keeps hot drinks hot and cold drinks cool. They work by using two non-touching layers: an outer one and an inner one. The inner layer comes in contact with the liquid, but essentially shields the outer wall. And a vacuum seal between them keeps air from seeping in. So the temperature of the liquid inside remains stable.
A similar concept works with double-wall glassware. And they work particularly well with coffee. You can pour hot coffee into the inner cylinder, while the outer layer is protected from the heat.
Plus, these types of glass mugs are also visually appealing, as you can see all the layers of your coffee drink, especially if you have a fancy one like a cappuccino or a macchiato!
Tips for safely using double-walled glasses with hot coffee
Thermal shock is more likely to occur when two temperature extremes exist, even with safer glasses. You can decrease that risk by lessening those sudden temperature changes. So instead of pouring hot coffee into a cold glass, warm up the glass first.
One way to do this is to let it sit at room temperature for a few minutes before adding the coffee.
Another way to warm up the glass slowly is to gradually pour coffee into it, rather than doing it all at once. This will help the temperature of the glass better match the higher temperature of the coffee without being “shocked.”
Plus, use double-walled glasses that have handles. That will help prevent the risk of burns.
And look for a heat-resistant mark or stamp on the bottom of the glass. This indicates it is safer to use with hot beverages.
Can you use a mason jar for hot coffee?
While mason jars do often come with handles, many are not heat resistant. So you could run the risk of the glass jar breaking or cracking if you pour hot coffee into it.
That said, mason jars can be a great option for iced coffee or other cold coffee drinks. Some even come with straws that fit through the lid, so you can securely seal up your iced coffee and sip it with confidence, without worrying about spilling it.
Why are coffee mugs commonly made from ceramic?
Though a ceramic mug can still be hot to the touch when hot coffee is poured into it, ceramic resists heat better than glass. The same goes for earthenware, which is porous and can absorb more heat, helping to prevent cracking.
Plus, ceramic cups do not take on flavors from drinks, or impart flavors to them, so they provide you with the most natural flavor of the coffee.
And the handle that usually comes with ceramic mugs are designed to be thick, so they’re safer to handle when the mug itself is filled something hot.
Can you use a glass with iced coffee?
Most glass is ok to use with iced coffee, as the temperature difference between cold coffee and a room temperature glass usually isn’t large enough to result in any breakage.
But you should avoid pouring iced coffee directly into a glass you’ve taken from a dishwasher, as it may still be hot. That could cause thermal shock and may damage or shatter the glass.
Can you heat up iced coffee?
If you’ve stored some leftover iced coffee in the fridge, you can absolutely warm it up without affecting its taste or texture. But your best option is to avoid using a glass mug.
A good choice is to do it on the stovetop. Simply transfer the iced coffee from your cup into a small saucepan and warm it up gradually on the stovetop. But don’t boil it as that could burn the coffee and make it acrid and bitter.
You can also heat it up in the microwave by first moving it to a ceramic coffee mug or another microwave-safe cup. Then heat it up for 90 seconds, checking every 30 seconds to make sure it doesn’t overheat and splatter inside your microwave.
It’s important to remember that not most glass is not suitable for hot coffee. If you want — or need — to use a glass, you have essentially two options:
- Thick glass made from borosilicate (essentially Pyrex)
- Double-walled glass coffee mugs
Since thermal shock is more likely to occur with rapid changes in extreme temperatures, like hot coffee meeting a cold glass, it’s a good idea to warm up your glass before adding the coffee to reduce risks of breakage. And look for heat-resistant glass.
Avoid using other types of glass, especially thin glass, as it could break or shatter after coming into contact with hot coffee. You could also burn yourself since glass can transfer heat better than a ceramic or earthenware mug, for example.
Metal is an efficient conductor of heat, so adding a metal spoon to your cup will draw heat from the coffee and cool it slightly. But an open cup of coffee will lose most of its heat by simply evaporating. So the effects of the metal spoon are negligible.
A transparent glass can be more visually impressive and a great way to show off the coffee. This is especially applicable with specialty coffees like a cappuccino or macchiato where the glass will allow you to see the distinct layers of the drink. But be sure you use heat-resistant or double-walled glass to help prevent it from breaking.
While stainless steel is very durable and will not be damaged by hot coffee, it can become very hot. So be sure to let the coffee cool a bit first. Picking up the stainless steel mug using the handle can also decrease the risk of getting burned, but that handle can still be hot.
More coffee answers
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