Can You Put Milk in A Coffee Maker?

Putting milk in a coffee maker seems like a great time-saving trick to make a freshly brewed and convenient cup of coffee, right? 

Nope. Not really.

Can you put milk in a coffee maker? No — it’s not that you can’t use milk, it’s that you shouldn’t. Coffee makers aren’t designed to work with a thick liquid like milk. Even if you did use it, adding milk to a coffee maker would just lead to a buildup of harmful bacteria and burnt flavor notes. 

Read below to learn more about how coffee makers work, why they work best with water, and why you really shouldn’t use milk.

How Coffee Makers Work

Apart from a few technical differences, almost every coffee maker in the market has more or less the same mechanics. 

Coffee makers, like pot/drip coffee makers or single-cup coffee makers, use hot water to steep coffee grounds. This water drips down through filters and collects in the pot below.

Drip coffee makers have a reservoir at the back that is filled with filtered water. 

Once you add water, the internal pipes, (or plumbing, if you will) carry it through the bottom of the machine into a section that contains the heating element. The heating element creates heat in a very controlled way. 

See, coffee brews best in water that is heated around 195F-205°F. This is why a circuit breaker makes sure that the power to the heating element switches off as soon as it reaches the right temperature. 

As the water is heated, steam starts to develop, which then travels through a separate piping system that delivers the hot water above the coffee grounds. 

The beauty of this system is that the steam doesn’t flow back into the reservoir thanks to a one-way valve — this keeps the water at a constant temperature while it steeps the coffee grounds!

As the coffee grounds steep, the collected coffee-infused water starts to drip down through a filter and slowly fills the pot. 

After some use, most coffee makers will require a cleaning cycle that will filter out any buildup of simple residue that is usually suspended in water. 

These machines are designed to clean themselves — but only when it involves minute mineral build-up from water. This is why things can turn ugly when you add anything other than plain water!

Can You Use Milk In Coffee Makers?

Now that you know how coffee makers work, let’s take a look at what happens when you switch from water to milk.

The biggest problem with using milk in coffee makers is that milk scalds at a significantly lower temperature than water. 

Remember how we said that most coffee makers heat water to 195F-205°F?

Well, if you replace water with milk, then you can bet that the coffee machine will burn the milk, which will add distinct burnt notes to the coffee. 

As soon as the milk enters the heating element, it will start to violently fizzle, which may even damage the piping of the machine over time. 

When the milk does go up to the right temperature, it will start to climb up the pipes at a much slower pace. 

This happens due to the density of milk — and the fact that it may take extra time to drip down through the filter due to the added milk solids.

When you do get a pot full of milk-infused coffee, you will notice its burnt flavor almost immediately.

Sure, the texture might seem okay, but ultimately, you will lose all those precious flavor notes that one typically associates with a properly brewed cup of coffee.

The final reason why you shouldn’t use milk in coffee makers has nothing to do with coffee, but what happens afterward!

Milk provides an excellent breeding ground for bacteria to grow and this can happen within two hours of using the coffee maker.

As the milk heats up inside the coffee maker, it will completely saturate the piping inside — and as anyone who has cleaned up after spilled milk or worked with milk will tell you, cleaning milk isn’t very easy!

While you may be able to clean the reservoir with clean water, you will not be able to thoroughly clean all the milk out of the internal piping of the machine. 

After a few hours, as the milk cools down, it will start to grow bacteria — and we are talking about dangerous bacteria: the kind that can make you ill!

Will Cleaning Help?

You might think that thoroughly cleaning the machine with fresh water will internally clear out all the milk solids and bacteria. 

Unfortunately, you would be wrong.

Even if you run a cleaning cycle on your coffee maker, there is no way to completely get rid of the milk solids in the linings of the pipe. 

You might have had to scrub the milk off the reservoir; well, unless you do the same to the pipes, they will remain contaminated. 

One could argue that the constant flushing of hot water in the pipes will likely kill the bacteria, but frankly, that won’t happen.

Keep in mind that most bacteria die above boiling temperatures (212°F) and most coffee makers only reach a maximum temperature of about 205°F. 

Sure, some bacteria may die at lower temperatures, but there are two sets of pipes: one travels from the reservoir to the heating element, while the other exits it and goes up to the steeping section.

The hot water might kill some bacteria from the steeping section, but it will have zero effect on the reservoir piping which will have tons of bacteria. 

Another point to consider is the toxins released by the bacteria which will likely survive hot temperatures, even if the bacteria don’t. 

This effectively means that you will end up with harmful bacteria or toxins in your cup each time you brew coffee in the contaminated machine!

In short, you are better off not using the same coffee maker again after you’ve run milk through it. Yes, it is that serious! So, please just avoid using anything but filtered water in your coffee maker. 

Related Questions 

Now that you know whether you can put milk in a coffee maker, here are some related questions.

Can you put coffee back in the coffee maker?

No, you shouldn’t put coffee back in the coffee maker to reheat it.

The added heat will not only destroy the precious flavor notes in the coffee, but the residue and coffee that ends up in the piping may even damage or clog the machine internally.

Can you put sugar in the coffee maker?

No, you can’t use sugar in the coffee maker. 

Sugar dissolved in water will not work either because the heating temperature in the machine will likely caramelize it, which will create a gooey mess that will eventually clog the machine. 

The sugar can also burn in the coffee maker, which will add a very bad aroma and flavor to your freshly brewed cup!

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