The Science of Drip Brewing: Everything You Need to Know About How Drip Coffee Is Made

People have been using automatic drip coffee makers for over 60 years now — ever since the Wigomat, the first electric drip machine, was invented in Germany in 1954. If you’re a coffee drinker, you’ve almost certainly had dozens, if not hundreds, of cups of drip coffee, and yet…most coffee drinkers don’t really understand the science behind how the machine works.

In this guide, I’m going to nerd out a little and explain it all. I’ll start by explaining the mechanics of a drip coffee machine, and then I’ll get into the nitty-gritty and explain the chemistry side of how coffee is made. Don’t worry, I promise to keep it light enough to understand. So, grab a cup of coffee, and let’s get started.

How Does a Drip Coffee Maker Work?

The actual mechanics of a drip coffee maker are very simple, and you might be surprised by the lack of moving parts if you open one up. There are a few pieces that every electric drip coffee maker has:

• Water Reservoir: The tank that holds water used for brewing.
• Heating Element: This is the piece of the machine that actually heats the water for brewing. In most cases, it loops underneath the heating plate so that it can heat water for brewing and simultaneously heat the carafe to keep your coffee hot.
• Water Hoses with a One-Way Valve: The heating element heats up the water in a small heating tank or tube. As the water expands and begins to boil, the pressure forces the water into a water hose that leads up to the shower head. The one-way valve prevents the water from flowing back into the reservoir.
• Thermometer: A thermometer is included with most modern coffee makers. This regulates the heating element and cycles it on and off to maintain a specific water temperature and prevent overheating.
• Shower Head: The shower head receives the water from the water hose and drips it down onto your coffee grounds.
• Filter Basket: The filter basket is a plastic piece that houses your filter. The filter basket sits directly below the shower head.
• Mesh Filter (optional): Some coffee makers include a permanent mesh filter that you can reuse. If you don’t have one of these, you’d use a paper filter in the filter basket instead.
• Spring-Loaded Stopper (optional but common): Most modern drip coffee machines have a spring-loaded stopper that prevents brewed coffee from flowing out of the filter basket. When the carafe is set in place on the heating plate, the stopper is pushed up and allows coffee to flow into the carafe. This mechanism is what allows for the “sneak-a-cup” feature.
• Carafe: The carafe is what collects the brewed coffee. It usually has a “patented no drip spout” that absolutely drips at least once on your counter when you pour, no matter what the company says.
• Heating Plate: The heating plate is what the carafe sits on. Since it’s usually located directly above the heating element, it continues to heat your coffee after it is brewed.

So, basically, water from the water reservoir is heated up by the heating element. As it expands and eventually boils, it’s naturally forced up the water hose to the shower head, where it drips onto your bed of coffee grounds and begins the actual brewing process. That’s right: most drip coffee machines don’t use a water pump! That’s why companies can sell them for $30 and still have them last for years.

Now that you understand how a drip coffee maker works, we can move on to the science behind what makes your drip coffee delicious…or not so delicious, in some cases.

The Actual Science Behind How Drip Coffee Makers Work

So, we actually already discussed a bit of science: the physics of how water is moved around inside your coffee maker. Water expands slightly — around 4% in volume — as it’s heated, and it eventually boils and creates an upward pressure within the tube.

So what about the science of brewing? Patience, young coffee lover.

“Brewing” coffee is the process of mixing hot water with coffee grounds to extract a bunch of compounds. These compounds include sugars found naturally in the coffee grounds, carbon dioxide, polyphenols, fatty acids, caffeine, flavonoids, and much more. There are over 1,000 compounds that get pulled out of coffee grounds when you expose them to hot water.

All of these compounds contribute to the flavor of your coffee and how thick or thin it feels when you drink it.

Since the exposure of coffee grounds to hot water is what extracts these compounds during the brewing process, it should stand to reason that changing a number of variables will affect the final product. These variables and the impact they have include:

• How long the coffee grounds are exposed to hot water: The longer you steep coffee grounds, the more compounds will be extracted.
• The temperature of the water: The hotter the water, the more quickly those compounds will be extracted. Each compound also has a different extraction rate relative to temperature, so things get very confusing very quickly when you try to track the effect of changing water temperature.
• The size of your coffee grounds: Finer grounds are less permeable and will hold water between the particles for longer. The longer exposure time to water plus the greater potential for extraction due to the increased surface area of the grounds means more rapid and more intense extraction.
• Your batch size: Changing the batch size will affect all three of the other variables.

Ultimately, drip coffee makers take the control of most of these factors away from the brewer in favor of convenience. You can still choose your grind size — provided you have a good, consistent grinder — but if you use the machine as intended, you can’t control the temperature of the water or how long the water is in contact with the grounds.

What Does This Mean for Drip Coffee Makers?

Drip coffee makers are generally looked down upon in the specialty coffee community because they remove control of the most important variables: water temperature and steeping time. Of course, there are some machines — like the Breville Precision Brewer — that give you that control, but these are quite expensive.

So what does the science behind extracting compounds from coffee look like in a standard drip machine?

How a Drip Machine Deals With Water Temperature

First off, and most importantly, in my opinion, drip brewers very often fail to reach a suitable brewing temperature, which is usually between 205 and 210 degrees (F) but almost always over 200. Even if it does reach these temperatures, it doesn’t maintain the temperature for the entire brew. Instead, you get lukewarm water from the shower head at first, which gradually heats up.

Reducing the water temperature you use to brew in this way will extract a lot of the fatty oils and acids from your coffee grounds. These include:

• Linoleic acids
• Oleic acids
• Palmitic acids
• And more

These compounds can make your coffee taste sour. This is why drip makers often yield sour coffee: they double down on extracting these sour-tasting compounds at the beginning of the brew because the water isn’t hot enough for full extraction yet.

Eventually, the water does get hotter, at which point the extraction of the sugars in your grounds begins to pick up. The sugars are, unsurprisingly, what gives coffee the rich sweetness it’s supposed to have. Unfortunately, the sugars aren’t usually extracted enough in a drip maker, once again because of the low water temperature for the beginning of the brew.

When you over-extract, which means you use very hot water and expose it to the coffee for longer, or you continue to heat the coffee after it’s brewed, the other plant matter and plant fibers begin to break down.

With longer extraction or heating times, you’ll begin to see an increased concentration of chlorogenic acid lactones and phenylindanes.¹ These compounds are excessively bitter and can very quickly ruin an otherwise good cup of coffee. Longer extraction times also pull out more caffeine, which is quite bitter.

Drip coffee machines won’t usually over-extract your coffee. However, most will continue heating your brewed coffee using the heating plate after the brewing process should be complete. These bitter compounds can still develop in brewed coffee void of grounds. This is why drinking coffee that has been sitting on a hot plate for hours tastes burnt and unusually bitter.

So…in most cases, people find that standard drip coffee is overly acidic, sour, and bitter. Now you know why!

How a Drip Machine Deals With Steeping Time

Steeping time is another important thing to consider when brewing coffee, and it’s another factor that is automated when you use a drip coffee maker. The shower head just dumps water on the bed of grounds, and it seeps through the coffee, through the filter, and exits into your carafe.

Ideally, you want to “bloom” your coffee, which is a term used to describe how coffee grounds expand and bubble when you add hot water to them. I recommend blooming for 30 to 45 seconds before continuing to add hot water to your grounds. What’s actually happening during this process is degassing; the grounds are releasing carbon dioxide.

If you don’t bloom your coffee before continuing to add water, then the carbon dioxide can disrupt the interactions between the grounds and the water as it continues to escape. Fewer interactions on a molecular level mean your extraction will be limited.

The shorter your extraction time — or the more the carbon dioxide interferes with the process — the more underdeveloped your coffee is going to taste.

This is why a lot of standard, run-of-the-mill drip machines make coffee that lacks flavor, in addition to being acidic and unpleasantly bitter.

Wrapping Up: Making Better Drip Coffee Using Science

So…now that you’re an expert on the science behind drip coffee makers, you’re probably wondering how you can improve your morning coffee. That’s what I like to hear!

There are two things you can do. First, you can buy a better drip machine. I recommend the Breville Precision Brewer. Although it’s quite expensive, it lets you dial in your preferred water temperature, control bloom time, control extraction time, and much more. You can also check out the Cuisinart CPO-800P1 PurePrecision Coffee Maker, which is much more affordable but still quite good.

Second, with a little effort and additional preparation each morning, you can drastically improve the performance of the drip maker you already own without spending any money. I wrote a complete guide on how to make better drip coffee at home and how each technique you can employ will improve the final cup.