Have you recently taken a sip of coffee only to find out that it tastes sour? Coffee can have many different attributes and flavors, but sour isn’t necessarily one that is desired. A great-tasting cup of coffee usually has a balance of different flavors and qualities that complement one another.
Sour-tasting coffee can be the result of a handful of different reasons.
Six Reasons for Sour-Tasting Coffee
- Stale coffee beans
- Under-extracted due to too coarse of a grind.
- Under-extracted due to not enough water used.
- Under-extracted due to lukewarm water.
- Under-extracted due to a short extraction time
- Under-roasted coffee beans
Let’s look further into each of these culprits and how to rid your coffee of that unwanted sour taste.
1. Stale Coffee Beans
Like most other food products, coffee beans can get old and stale over time. As coffee beans sit for long periods, they begin to lose their freshness. Evaporation of the aromatic oils co-occurs as the sugars disintegrate. Unfortunately, this can lead to your coffee tasting sour.
Once this happens, the natural acids of the coffee beans will turn sour, and your cup of coffee will, in turn, have a sour taste.
Fairly soon after your coffee beans are roasted, they begin to lose their freshness. Depending on how you are storing them, this time frame can change. Check out our other article, “How to tell if your coffee beans have gone bad.“
*TIP: Storing your coffee beans in the freezer can help extend their shelf life. Click here for more info.
One of the top ways to keep your coffee fresh for longer is to buy whole coffee beans over grounds and purchase a coffee grinder. Then only grind what you need for the day. Additionally, it helps to buy speciality coffee, not Robusta beans, from a quality roaster to ensure your beans are at their freshest when you get them.
What is Extraction?
Before we get into under extraction, let me first explain extraction. Extraction is the process of pulling the flavor out of the coffee bean through hot water. When water is combined with coffee grounds, a chemical reaction dissolves the flavor compounds.
Acids are the first to be extracted from the coffee grounds. This is why the first bit of coffee brewed will taste sour. Once the brewing process has finished, oils, sugars, and other flavors will have had enough brewing time to be extracted from the coffee grounds. These are what balance out the sourness from those initial acids.
Under extraction is when the coffee isn’t brewed for long enough for the good flavors from the beans to be produced. What you are left with is an unbalanced cup of coffee.
2. Under-Extracted Coffee: Using Coarse Grinds
Grinding your coffee beans can take some practice. Two things will dictate the fineness or coarseness of the grind size you’re looking for. First, the brewing method significantly determines how fine or coarse your grounds should be.
For instance, if making an Espresso, your grind size should be very fine, like the size of table salt. If using an Aeropress, then your grind size will be a bit more coarse but still fine. On the other end of the spectrum, the grind should be coarse when using a French Press.
Below you’ll find a table explaining with greater detail how fine or coarse your grind should be depending on what device is being used to brew with. Or for more info, check out our article, “How fine should I grind my coffee beans?”
Additionally, the amount of coffee you make will determine the coarseness of your coffee grind. Typically, the more coffee you make, the more coarse your grind should be.
When the coffee grind is too coarse, the water will pass through too quickly and not be able to extract enough of the coffee flavor in the process. When your grind is the correct size (not too coarse), there is more surface area of the coffee, allowing the water to extract more of the coffee flavor.
For further explanation of how to determine how fine to grind your coffee beans, click here!
3. Under Extracted: Wrong Coffee-to-Water Ratio
Determining the appropriate amount of water to use in brewing the perfect cup of coffee may take some trial and error. Personal preference also influences how much water you’ll want to use, but keep in mind that too little water will affect the taste.
Using too little water in the brewing process can lead to sour-tasting coffee. If only using a small amount of water, the coffee is not allowed the entire time it needs for the full flavor to be extracted from the coffee grounds. This will lead to that sour taste.
If you want to read more about how much water to use, check out our other article, “What is the best coffee to water ratio?”
4. Under Extracted: Wrong Water Temperature
Unfortunately, under extraction can result from your coffee maker not functioning correctly. If your coffee machine is older, it may have difficulty heating the water to the needed temperature.
When this occurs, water has a difficult time extracting. As a result, all the good oils and coffee flavors are prevented from being fully extracted, and the taste of your coffee will suffer. What you end up getting is underdeveloped sour coffee.
You’ll want the water to be between 195 and 205 degrees Fahrenheit, which is a tad bit cooler than the boiling point of water (212 degrees Fahrenheit).
NOTE: If your water exceeds 205 degrees, your grounds will be over-extracted and produce bitter-tasting coffee. Also, keep in mind that if you live at a higher elevation, water will boil at around 195 degrees.
Consider reading: Should I Brew Coffee With Boiling Water?
5. Under Extracted: Short Extraction Time
Depending on what coffee brewing method you’re using, you may not be brewing for long enough. If you’re using an immersion brew or pour-over, you can control how long extraction is. If using a drip machine or Keurig, you may have something wrong with the device.
When the brew time is too short, the water does not have enough time to extract all the good oils and flavor from the coffee grounds.
Different compounds of the grounds are extracted at different times of the brewing process. If not enough time is allowed, only the fats and acids are extracted resulting in a sour taste.
If using a French Press, add about twenty seconds before pushing down the filter. If using a pour-over, just pour the water slower than previously done.
6. Under-Roasted Coffee Beans
When coffee tastes sour, it is typically due to under-extraction, but sometimes it is an issue with the roasting process. When beans are roasted, they go through chemical changes, Maillard reaction. During the process, the natural flavors and aromas of the coffee beans become pronounced.
When a batch of coffee beans are stopped too early in the roasting process, instead of making the desired sweetness, you’ll end up with sour flavors.
How to Fix Sour Coffee?
Before we finish up, let’s quickly go over what to do if you’re dealing with sour coffee.
- Buy fresh beans
- Use finer grind size
- Use more water when brewing
- Use hotter water (not boiling)
- Lengthen extraction time
- Ensure your beans are high-quality Arabica beans
Last Notes Sour Tasting Coffee
I recommend only trying one of these fixes at a time. If you do all of them at once, or just two, you won’t necessarily know which problem you were having and will most likely end up with an over-extraction cup of coffee. And no one wants a bitter taste in their cup of coffee.
Hopefully, you’ll be able to determine the cause of your coffee tastes sour after reading this and doing your investigative work. Remember to check your coffee beans first for staleness, and then if that isn’t the cause of your salty coffee, follow our other recommendations on preventing under extraction.
If your coffee is tasting more bitter after trying the suggestions listed, you now have a whole other issue. Click here to learn how to fix bitter coffee.