Why Are My Tomatoes So Acidic? (3 Causes of Acidic Tomatoes)


Have you had it with acidic tomatoes?  If so, you’re probably wondering why the tomatoes from your garden are so sour.

So, why are your tomatoes so acidic?  Certain tomato varieties will taste more acidic than others, due to differences in acid and sugar content.  The amount of sunlight a tomato plant gets will also affect the acidity of the tomato fruit.  The ripeness of a tomato will affect acidity as well.

Of course, if you’ve already harvested your tomatoes, there isn’t much you can do to change their acidity.  However, there are steps you can take to grow tomatoes that taste less acidic.

We’ll get into that soon enough.  Right now, we’ll start by taking a closer look at why tomatoes taste acidic.

Let’s begin.

Why Are My Tomatoes So Acidic?

Tomatoes that have high acid content and low sugar content will taste more acidic.  According to this article on acid in tomato juice from Wiley:

“Reducing sugars and organic acids are significant components of, respectively, the sweet and sour tastes in tomatoes. Their concentration may significantly affect flavor acceptability.”

https://onlinelibrary.wiley.com/doi/full/10.1111/j.1745-4557.2007.00119.x
cherry tomatoes
Cherry tomatoes tend to be sweeter and taste less acidic than larger tomatoes.

There are many different acids in tomatoes that can affect their flavor.  Two of the major acids in tomatoes are citric acid and malic acid.

There is more citric acid than malic acid in tomatoes.  The amount of acid depends on a few major factors, including:

  • Variety of tomato grown
  • Amount of sunlight
  • Ripeness of fruit

Variety

The variety of tomato you grow will have a big impact on how acidic the fruit tastes.  In a small study of 15 tomato varieties, the Utah State University Extension found that heirloom tomatoes were less acidic (had higher pH) than hybrid tomatoes.

According to the Colorado State University Extension:

“Although tomatoes are considered a high-acid food (pH below 4.6), certain conditions and varieties can produce tomatoes and tomato products with pH values above 4.6.”

https://extension.colostate.edu/topic-areas/nutrition-food-safety-health/canning-tomatoes-and-tomato-products-9-341/

Tomatoes taste best when they have a good balance of acid and sugar.  However, preferences will vary depending on individual palate!

There are three basic types of tomato flavors, based on combinations of acid (sour) and sugar (sweet).

Sweet (High Sugar)

These tomatoes taste sweet, since they have lots of sugar.  Some examples of sweet tomatoes include:

tomato plant with fruit
Cherry tomatoes such as Super Sweet 100 have a sweet taste, and they produce lots of little fruits on one plant.

Sour (High Acid)

These tomatoes taste tangy, tart, or sour, due to their low sugar content.  Some examples of sour tomatoes include:

Green Zebra tomato
Green Zebra tomatoes are green with yellow stripes when ripe.
Image from: https://commons.wikimedia.org/wiki/File:Green_Zebra_Tomato_65.jpg

Balanced

These tomatoes are both sweet and sour, due to their balanced mix of sugar and acid.  Some examples of these balanced tomatoes include:

Cherokee Purple tomato
Cherokee Purple tomatoes tend to grow large and have a dusky pink or purple color.
Image from: https://commons.wikimedia.org/wiki/File:Cherokee.purple.jpg

Amount of Sunlight

Tomatoes grown in full sunlight tend to be more acidic.  Tomatoes grown in shade or reduced daylight hours tend to be less acidic.

The amount of sunlight a tomato plant gets will affect how the fruit ripens.

Ripeness of Fruit

Tomatoes picked before they are fully ripe will be more acidic.  Green tomatoes will still be hard, but they will get softer and sweeter as they ripen.

Tomatoes allowed to ripen off the vine will also be less acidic than tomatoes ripened on the vine.  For some tomatoes, it will be hard to tell whether they are ripe just by looking at them.  For example:

  • Green Zebra tomatoes are green with yellow stripes when ripe.
  • Black Krim tomatoes look dark red, purple, or even black when ripe.
  • Cherokee Purple tomatoes look deep crimson when ripe.

To tell when these tomatoes are ripe, you may need to feel them to see if they are soft enough.  If you harvest too early, you will end up with more acidic tomatoes that taste sour.

If you want less acidic tomatoes, then don’t worry about bruising them a bit when checking their ripeness.  Perfect, unblemished fruits tend to be more acidic than ones with a little bruising.

Temperatures that are too high (or too low) will slow down or stop the ripening process.  This could lead to tomatoes that are bitter or flavorless instead of sour, sweet, or balanced.

Excessive sunlight can cause uneven ripening (such as green or yellow shoulders on the top of fruit).

You can learn more about what causes tomatoes to ripen in my article here.

What Else Makes Tomatoes Acidic?

There are a couple other factors that can make tomatoes acidic, including:

  • Watering
  • Location

Watering

The concentration of acid and sugar in a tomato will affect its flavor.  More water means a lower concentration, and less water means a higher concentration.

watering can
A lack of water can cause more acidic tomatoes, as well as nutrient deficiencies in your plants.

Think about it: if you dissolve a teaspoon of sugar in 1 cup of water, it will taste sweeter than the same teaspoon of sugar dissolved in 2 cups of water.

With less water, sugar will taste sweeter, and acid will give a stronger sour taste.  In a dry growing season (or in a dry location), tomatoes will have less water content.

Location

It seems strange, but the location where you grow your tomatoes can totally change the flavor profile.  The exact same variety grown on opposite sides of the country can have a different acidity or sweetness.

This may be due to differences in sunlight, watering, or soil types (clay vs. sand, calcium-rich or calcium-poor, etc.)

Just keep in mind that it might take a little experimenting to see which varieties grow sweet, sour, or balanced in your location.

What Makes Tomatoes Taste Sweet?

Of course, the sugars in tomatoes make them taste sweet.  However, that isn’t the whole story.

Tomatoes also contain aroma volatiles that can affect the flavor you experience when you eat them.

According to this article from cell.com:

“Aroma volatiles make contributions to perceived sweetness independent of sugar concentration, suggesting a novel way to increase perception of sweetness without adding sugar.”

https://www.cell.com/current-biology/fulltext/S0960-9822(12)00408-3

Aroma volatiles do this in two ways:

  • When they are inhaled through nose (when you smell a tomato)
  • When they come up into the nasal passages after chewing and swallowing (when you eat a tomato)

Conclusion

Now you know why your tomatoes are so acidic, and why they end up tasting sour or tart.  You also know some ways to grow tomatoes that taste a little less acidic.

I hope you found this article helpful.  If so, please share it with someone who can use the information.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!

~Jonathon

jonathon.david.madore

Hi, I'm Jonathon. I’m the gardening guy (not guru!) who is encouraging everyone to spend more time in the garden. I try to help solve common gardening problems so that you can get the best harvest every year!

Recent Content