Why Coffee Taste Sour Sometimes

Why Coffee Taste Sour Sometimes

The last thing anyone wants when finally getting to sit down with their favorite cup of coffee is for something to go wrong. It can ruin a person’s morning or day in general when their coffee isn’t up to their usual standards, especially if it results in them not getting their caffeine fix.

The most common and predominant issue coffee drinkers face is the beverage having soured.

Everyone who loves coffee will tell you that there is nothing worse than when they get their much-anticipated cup only to find it has soured.

The Cause of Sour Coffee

There are a few reasons that can lead to the souring of a cup of coffee. They will result in the unpleasant taste that many experience. For some, it can even completely ruin the beverage for them if it is potent enough or simply just not up to the standards that they are accustomed.

One of the most common reasons for a sour cup of coffee is that it was under-extracted during the making process. The ideal number for extraction is around 18-20% of total dissolved solids or TDS.

This is in juxtaposition to over-extracted coffee which can lead to a more bitter taste being created.

The difference between the two is the flavor that has been affected and which elements will be brought out first to the drinker. Both are powerful but the sour taste is more tart and acidic while the bitter flavor will be more intense in a way similar to that of dark chocolate.

Here is a deeper comparison of the taste of over vs under extracted coffee.

Some of the key issues behind sourness of coffee stemming from under-extraction are:

  • When the coffee maker uses too coarse of grounded coffee beans it can lead to the sour taste that may be present. If this is the case it can be necessary to make the grounds finer before using. This will prevent the powerful acidic taste.
  • Another possibility that could be causing the sourness in the drinker’s coffee is the amount of time spent brewing. When coffee is brewed for too long it can lead to the sour taste that many hope to avoid. Individuals should try changing their brewing time to prevent this possibility entirely.

The Acidic Properties of Coffee Cause Sour

The relationship between sourness and coffee is one that has been around as long as the beverage itself. It has been the prevailing problem coffee drinkers have continued to face and one that will likely remain prominent.

Often people even come to associate a sour taste with coffee because they are trying to prevent the bitters from overwhelming a batch of coffee – but that doesn’t always have to be the case.

Because of its commonality, it is an issue that most people will need to address at a certain point. If the problem has become repetitive and inhibited the drinker’s enjoyment of the coffee then it may be time to change things up.

The steps above are some of the easiest changes to make that will still have a massive impact on the overall taste of the beverage itself, hopefully solving the unwanted sour taste.

Is Sour Coffee Bad For Your Health?

In no way, other than to your taste buds, is sour coffee bad for you.

Sour coffee is the product of under-extraction during the brewing process, and occurs when an unbalanced amount of the coffee’s antioxidants, oils, and caffeine are present in the resulting beverage. Usually their are more acids in the cup than other flavor compounds.

How Do I Stop Under-Extraction From Occurring?

Most commonly, under extraction is a consequence of a poor brewing process.  The easiest way to stop coffee from under extracting, and subsequently stop sour coffee from ending up in your coffee mug, is too analyze your brewing method to realize where it has started to go wrong.

The most common factors of the brewing process that can lead to poor flavor:

  1. Brewing Time
  2. Agitation
  3. Coffee Grind Surface Area
  4. Amounts of Water Used

What’s important to remember however is that any poor flavor you get with your coffee doesn’t make it bad for you. All sour notes are natural acids that extract in excess of the sugars and bitters that typically come in a balanced cup.

You don’t even get any additional acids in your coffee either, sour coffee only tastes that way due to underextraction of the other types of dissolved solids discussed earlier in this article.

This leads us to one additional question I hear from time to time.

Does Old Coffee Get More Acidic Over Time?

Coffee often gets a bad reputation as an overly acidic beverage. However, on average coffee is around a 5 on the PH scale, but is old coffee more acidic?

Acidity is Relative

Since coffee is not an overly acidic beverage it may seem strange to hear of people constantly referring to coffee as an acidic beverage.

Most commonly, when coffee consumers refer to their beverage as being acidic they are referring to a good thing. The acidic quality of coffee is responsible for most of its flavor profile, and perfecting this acidic taste is the goal of most coffee enthusiasts.

As a consequence of this distinction, when we are asking does old coffee get more acidic over time, we are actually asking two different questions:

  1. Does coffee’s PH decrease over time?
  2. Does coffee’s flavor increase over time?

The PH of Old Coffee

When coffee sits too long a reaction between the beverage’s hydrogen molecules and the beverage’s oxygen molecules occurs.

This reaction is called oxidation, and this continued oxidation of the beverage will lead to a decrease in PH levels.

The Flavor of Old Coffee

Due to the continued oxidation and the beverage’s decreased PH level, it may seem as if old coffee will produce a more vibrant flavor profile. However, old coffee will most likely always produce stale or bitter results as the acid level decreases and the grounds oxidize losing freshness.

Old coffee almost never tastes sour, it usually will taste stale or as I like to call it, musky.

How Long is Too Long?

When it comes to brewing coffee and letting it sit, the window for consumption is actually quite short. It is commonly suggested that coffee should be let sit for no more than 30 minutes before consumption.

If you have to let your coffee sit or you made too much and need to store it, it is best if you try to keep it as warm as possible. Storage in an insulated thermos is most recommended. For added heat and preservation, one can wrap the respective thermos in a steamed or warmed towel.

This added layer of heat will allow the coffee to keep its temperature for a longer period of time, delaying the oxidation process.


Aubrey, A. (2006, September 28). Coffee: A Little Really Does Go a Long Way. Retrieved from https://www.npr.org/2006/09/28/6155178/coffee-a-little-really-does-go-a-long-way

Brian Mounts

Head blogger, editor, and owner of "Top Off My Coffee", a website that has been educating readers about coffee brewing techniques and equipment since 2012.

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