What Is Weak Coffee?

Did you ever take a sip from your coffee and immediately felt like your cup tastes less like freshly brewed coffee, and more like water that has gone sour for some reason?

The first cup of the morning is something we all look forward to before starting a long day at the office, but unfortunately, sometimes that cup doesn’t really meet our expectations. Brewing coffee is a delicate matter, and even a slight mistake can turn the beverage we all love into an undrinkable mess.

Weak coffee is caused by various factors, but the most common culprits are using a higher than the ideal ratio of coffee to water and not letting your coffee brew long enough. In both scenarios, your coffee will end up being under-extracted, creating a drink that tastes sour and flat with a watery consistency.

Coffee Strength vs. Coffee Extraction

When we are talking about what makes coffee weak or strong, it’s important to understand the concepts of coffee strength and coffee extraction.

Technically speaking, coffee strength refers to the amount of coffee dissolved in water. Given that we have a fixed amount of coffee grounds, brewing with a smaller amount of water than ideal will make our coffee too strong, while brewing with a larger amount will make our coffee too weak.

On the other hand, with a large amount of water our coffee would be over-extracted, but with a small amount of water, it would be under-extracted. So, the stronger coffee will end up tasting sour and flat due to under-extraction, while the weaker coffee will be bitter due to over-extraction.

In daily life, we would be referring to the under-extracted coffee as weak even though it’s technically stronger. Truth be told, strength is used in a lot of different contexts in the coffee world, so it’s only natural that things get confusing at times.

For this reason, we will be talking about flavor and mouthfeel when we use the words “weak”, and “strong” in this article.

What Does Weak Coffee Taste Like?

Weak coffee is often described as sour, flat, and watery. Considering that under-extracted coffee only contains the acidic components of a coffee bean, this description indeed makes sense. 

After all, the flavor and the mouthfeel which we associate coffee with come from the coffee oils that are extracted further down the process.

What Causes Weak Coffee?

With so many different reasons which can cause your coffee to turn out weak, it’s best that we go over every single one of them in order to have a complete idea about what could actually go wrong.

High Coffee to Water Ratio

Getting the coffee to water ratio wrong can affect your coffee in two different ways, depending on the ratio being too high, or too low. If you used way too much coffee, you’ll notice that your brew is sour and flat, and if you used too little coffee, you’ll notice that your brew is extremely bitter. 

Weak coffee is actually a result of too much coffee being used, which prevents the components that provide flavor and body from being extracted.

Fortunately, there is a widely accepted standard that tells us exactly how much coffee should be used with a certain amount of water, and following this standard will ensure that you get the measurements right every single time.

The standard which is developed by the Specialty Coffee Association of America (SCAA) is known as the “Golden Ratio” in the coffee world, and it states that for each gram of coffee, roughly 18 grams of water should be used.

With some simple calculations, we can find out that a standard 8 oz. cup of coffee requires roughly 0.36 oz. of ground coffee for 8 oz. of water. In Metric units, this would be 10 grams of ground coffee for 180 ml of water.

Please note that these measurements are very delicate, which is why it’s quite hard to approximate the correct amounts with the naked eye. Investing in a kitchen scale is a great idea to ensure that you always get the measurements right, and leave no room for error on this front.

Brewing Temperature

Brewing temperature plays an important role in determining the strength of your coffee. If the temperature is way too low, your coffee will be under-extracted, meaning that your cup will lack a lot of the compounds that give coffee its flavor and body. The amount of caffeine in your cup is also closely related to the extraction level, and an under-extracted cup of coffee contains less caffeine than a properly extracted one.

The ideal temperature for brewing coffee is between 195 and 205 degrees Fahrenheit. By ensuring that you brew your coffee in this temperature range, you will eliminate the problems caused by brewing at the wrong temperature.

While most automatic coffee machines are automatically adjusted to use this temperature range, it wouldn’t hurt to double-check with the help of a kitchen thermometer in any case.

The Freshness of Coffee Beans

As soon as coffee beans are roasted, they slowly start going stale. While this process can be decelerated with proper storage, a lot of people don’t realize how quickly coffee beans can lose their freshness in the wrong conditions.

Since coffee beans don’t really go “bad” in the traditional sense for a long time, it is mostly assumed that it’s fine to keep them around for a long amount of time without caring too much for storing conditions. In reality, this causes coffee beans to lose a huge part of their flavor without being noticed. To put it into perspective, it could take as short as a few days for your coffee beans to lose most of their flavor if stored improperly.

To ensure that your coffee doesn’t end up weak because of this, make sure to always buy fresh beans, and store them in airtight containers at room temperature where they aren’t exposed to direct sunlight. Ground coffee will lose freshness even quicker due to having a larger surface area, so grind only as much as you need.

Grind Size

Similar to brewing temperature, grind size is also a determining factor in how extracted your coffee will be. While the optimal grind size depends on the brewing method used, a general rule of thumb is that as grind gets coarser, the extraction rate slows down.

By this logic, we can conclude that coarser grinds require more brewing time, whereas finer grinds require less. While quicker brewing methods such as espresso and Moka pot benefit from finer grinds, methods that take longer such as cold brew and french press require the grind size to be coarse. For automatic drip coffee makers, a medium grind size will work just fine.

Next time you brew your coffee, make sure to check the size of your grind as it very well could be the reason behind your brew ending up weak.

Brewing Time

Just like brewing temperature and grind size, brewing time also plays a role in the extraction level of your coffee. A brewing cycle that is cut short will once again cause your coffee to be under-extracted, and you will face the same set of problems as you did by using the wrong brewing temperature or grind size.

If you checked every box in this list so far and your coffee still tastes weak, there is a good chance brewing time is the culprit. Since brewing time depends on the brewing method and the grind size you’re using, it’s not possible to say that a certain amount of time is absolutely the right way to go.

By increasing the brewing time in small increments, you can experiment and find the optimal brewing time for yourself.

How to Fix Weak Coffee?

Sometimes you brew a pot of coffee only to find out that it’s extremely weak. While brewing a fresh pot is the best option, not all is lost if you don’t want your coffee to go to waste. 

Here are a few tricks you can use to revive your coffee.

Brew Again

Since weak coffee is caused by under-extraction, you can simply brew again with the same coffee grounds. This process will help to extract the components that weren’t extracted in the first brew cycle.

Note that your coffee may end up over-extracted because of this, but it’s worth a try.

Add Instant Coffee

Adding a small amount of instant coffee can help to add flavor to your weak coffee. Try not to add too much at once to make sure that your coffee doesn’t get way too bitter.

Add Flavored Syrups or Sugar

By adding some flavored syrup to your weak coffee, you can replace the sour taste with something sweet. If you don’t have any flavored syrup handy, you can also try adding some sugar.

Make Ice Cubes

This isn’t much of a fix, but you can use your weak coffee to make coffee ice cubes for the next time you have iced coffee. By using coffee ice cubes in your iced coffee, you can prevent your coffee from being watered down.

How do I Make My Coffee Less Strong?

If the flavor of your coffee is too overwhelming for you, you can always weaken the taste by diluting it.

Depending on your preference, you can add some water, milk, or even cream to your cup, which will cut the bitterness and acidity down.

If you have a sweet tooth, flavored syrups are also a good option to mask the bitter taste of coffee, and give it some flavor. 


Weak coffee can definitely be a nightmare, but it’s also quite easy to avoid if you follow the rules. If you give enough care to your brew, you can be sure that it won’t let you down.

Unfortunately, there will be times where you won’t have a say in how the coffee is brewed, so you won’t be able to really do much to prevent a weak coffee nightmare from happening at some point. It’s just something we have to live with as coffee lovers.

Or perhaps, you could carry your own coffee around to completely avoid this situation 🙂

Have a great day, and enjoy your coffee!