Low-Acid Tomatoes: Science Reveals Which Varieties Are Actually Least Acidic

For many people, tomatoes can be surprisingly difficult to enjoy. A slice on a sandwich or a bowl of fresh salsa can quickly turn into heartburn or indigestion. It’s no surprise that gardeners and shoppers alike go looking for low acid tomatoes.

But finding clear answers isn’t easy.

Some sources claim that yellow tomatoes are less acidic, while others insist that all tomatoes have essentially the same acidity. Gardeners are left wondering whether choosing the right variety can actually make a difference—or if low-acid tomatoes are just a myth.

The good news is we no longer have to guess. In one of the most comprehensive studies of tomato flavor chemistry to date, researchers measured organic acid levels across more than 150 varieties grown in multiple environments.

The results were striking: some tomatoes contained nearly four times as much acid as others.

In this article, we’ll look at what the science actually shows—which types of tomatoes tend to be lower in acid, which specific varieties ranked lowest in measured acidity, and why factors like fruit size and flavor concentration can influence how acidic a tomato seems.

If you’ve ever wondered whether choosing the right tomato might make them easier to enjoy, the data finally gives us some answers.

While we used to rely on subjective descriptions of a variety—for example, how it tastes—to guess its acidity, we now can use data.  German Johnson is among the least acidic varieties identified in the study.

What Actually Makes Tomatoes Acidic?

When we talk about acidity in tomatoes, we’re really talking about a small group of organic acids that naturally accumulate in the fruit during development. Two acids dominate:

• Citric acid – the primary acid in tomatoes and the largest contributor to their bright, tangy flavor
• Malic acid – present in smaller amounts but still important to the overall acid profile

Together, these two compounds account for the vast majority of measurable acidity in fresh tomatoes. In flavor chemistry studies, researchers often report the total organic acids as the sum of citric and malic acid, which provides a convenient way to compare varieties.

But how acidic a tomato tastes is not determined by acids alone.

Sugar Can Mask Acidity

Sweetness strongly influences how our brains perceive acidity. Honey and orange juice provide a useful example. Both typically fall within a similar pH range—roughly between about 3.3 and 4.0—yet orange juice tastes distinctly tart while honey rarely tastes acidic at all. The difference lies in sugar. Honey contains extremely high concentrations of sugar, which overwhelm and mask the sensation of acidity.

The same interaction happens in tomatoes. Varieties that accumulate more sugars can taste sweeter and more balanced, even when their acid levels remain relatively high.

Flavor Intensity Can Also Change Perception

Another factor that complicates things is aroma.

Much of what we experience as “tomato flavor” actually comes from volatile aromatic compounds produced when the fruit is cut or chewed. These compounds create the characteristic green, fruity, and savory notes we associate with a good tomato.

When a tomato lacks many of these aromatics—as is often the case with modern supermarket varieties—the fruit can taste bland or mild. That mildness can easily be interpreted as lower acidity, even when the actual acid content is unchanged.

In other words, a tomato can taste gentle while still containing plenty of acid. As many tomato lovers have discovered, the stomach sometimes notices what the palate misses.

First impressions can be deceiving. With its rich, classic tomato flavor, Rutgers isn’t typically thought of as low-acid—but the study found it contains about 31% less acidity than the average tomato.

The Low-Acid Tomato Controversy

For decades, gardeners and cooks have argued about whether “low-acid tomatoes” really exist.

Some sources insist that the idea is a myth. Others swear from personal experience that certain tomatoes seem noticeably gentler on the stomach. The debate has been fueled by one commonly cited statistic: tomatoes almost always fall within a narrow pH range of roughly 4.1 to 4.7.

At first glance, that range appears small, leading many writers to conclude that there is little meaningful difference between tomato varieties.

But the story behind that number is more interesting.

In the 1970s, the USDA began investigating tomato acidity after consumers raised concerns that newer tomatoes—particularly yellow-fleshed varieties—might be becoming less acidic over time. My suspicion is that people were actually noticing the loss of flavor in many modern tomatoes—a trend that is now well documented—and interpreting those milder flavors as lower acidity.

The concern carried real consequences. If tomatoes were truly becoming less acidic, they could potentially exceed the pH safety threshold of 4.6 used in home canning, requiring added acid such as lemon juice or citric acid to prevent the growth of Clostridium botulinum.

Fortunately, the research put those fears to rest.

Across many varieties, tomatoes consistently remained safely below the canning safety threshold. The popular belief that yellow tomatoes were inherently less acidic and unsafe to can also proved unfounded.

What remained from that work was the now-famous pH range of roughly 4.1 to 4.7, a statistic that has sometimes been used to argue that tomato varieties do not differ meaningfully in acidity. I’ll admit that when I first encountered it, I was skeptical too.

There's probably a reason Beefsteak is so universally beloved.  With a low acidity and a good bit of sugar to balance it out, this variety strikes the perfect balance of sweetness and tang.

A Perspective Shift

But there are two important things to remember.

First, most foods we consume naturally fall within relatively narrow pH ranges. My household happens to contain a budding young scientist who has taken to measuring the pH of nearly everything in the kitchen. The vinegar in our pantry measures around pH 3, while the sweet tea in our refrigerator comes in close to pH 5. Those two modest pH units make a dramatic difference in both flavor and how our bodies respond.

Second—and more importantly—the pH scale is logarithmic.

That means each one-unit change represents a tenfold change in acidity. Even a small difference can therefore translate into a substantial chemical change. For example, a tomato at pH 4.1 contains about four times as many free hydrogen ions as one at pH 4.7.

In other words, small numbers on the pH scale don’t always lead to small consequences.

And as we’ll see in the next section, when scientists measure the actual acids inside tomatoes, the differences between varieties turn out to be much larger than pH alone might suggest.

Perhaps it's the rich, wine-like color that leads one to assume that a tomato like Black Prince would be acidic, but this is not the case.  In fact, this variety ranks among the least acidic tomato varieties, according to data from Tieman et al.

Tomato Acidity Varies Widely

Once we move beyond pH and look at the actual acids inside tomatoes, a much clearer picture emerges.

In a comprehensive flavor chemistry study conducted by researchers at the University of Florida, scientists measured the concentrations of citric acid and malic acid across more than 150 tomato varieties grown in multiple seasons and environments. Using the published dataset from that study, I analyzed the results with a statistical model that adjusts for year and growing location, allowing the varieties themselves to be compared more fairly. The values shown below represent adjusted mean acid concentrations for each variety.

When those adjusted values are ranked from lowest to highest, the variation between tomatoes becomes immediately apparent.

A wide range of acidity is observed among the 154 tomato varieties included in the study.  Here, the varieties are assorted according to their total acid content (citric + malic acids), which has been statistically adjusted to account for location and year effects.

Across the varieties tested, total organic acids ranged from roughly 2.2 mg/g to more than 8.7 mg/g of fresh weight—nearly a fourfold difference between tomatoes.

That’s a much larger spread than the narrow pH range discussed earlier might suggest, although mathematically speaking, it's right in line. 

For gardeners and tomato lovers searching for varieties that are easier on the stomach, this is encouraging news. It suggests that variety choice really can influence acidity.

But the data also reveal something even more interesting: the differences between tomatoes are not random. Certain types of tomatoes tend to cluster toward one end of the acidity spectrum.

To understand why, we need to look at a few broader patterns in the data.

People have long assumed that color has an impact on acidity, with yellow varieties often being touted as less acidic.  This, as we will soon learn, is not true.  Fortunately for yellow tomato lovers, there are certain varieties, like Hillbilly, that really are less acidic.

Do Tomato Colors Affect Acidity?

One of the most common beliefs about tomatoes is that yellow varieties are less acidic than red ones. This idea has circulated in gardening books and kitchen lore for decades, and it likely stems from the fact that yellow tomatoes often taste milder and sweeter.

But as we discussed earlier, flavor perception can be misleading. Sweetness and aroma both influence how acidic a tomato seems, even when the underlying chemistry tells a different story.

To see whether tomato color actually correlates with acidity, I grouped the varieties in the dataset by their primary fruit color and compared their adjusted mean organic acid concentrations.

Acid content among different colors of tomatoes.  Cherry types were removed from this analysis for reasons that will be discussed later.  As you can see, color does not impact acidity.  Narrower ranges observed for certain color classes are most likely caused by a small sample size.

The results show that acidity is distributed across all color classes. Red, pink, yellow, orange, green, and dark-fruited tomatoes all span a fairly wide range of acid concentrations.

It’s important to note, however, that some colors appear to have narrower ranges simply because fewer varieties were included in those groups. With only a small sample, there’s less opportunity to capture the full range of variation. Green tomatoes, for example, appear slightly more acidic—but that result is based on just two varieties. By contrast, red tomatoes were sampled extensively, making it much more likely to identify both very low- and very high-acid examples.

This finding helps explain why the long-standing claim that yellow tomatoes are inherently low in acid has never held up well in controlled studies. While individual yellow varieties may fall on the lower end of the spectrum, many others contain acid levels comparable to their red counterparts.

If color doesn’t provide a clear answer, another characteristic of the fruit does show a stronger pattern.

It turns out that size matters.

Currant varieties like Texas Tiny are known for their intense flavor. That intensity, it turns out, comes with a higher acid content.

Why Small Tomatoes Tend to Be More Acidic

While tomato color shows little consistent relationship with acidity, fruit size reveals a much clearer pattern.

To explore this, I grouped the varieties in the dataset by fruit size—cherry, salad, medium, and large—and compared their adjusted mean organic acid concentrations.

As fruit size increases, acidity decreases. Cherry tomatoes tend to have the highest acidity, while large beefsteak-types trend towards lower total acid content. This may serve as a useful starting point for gardeners looking for low acid tomatoes.

The results show that smaller tomatoes tend to contain higher concentrations of organic acids than larger fruits. Cherry tomatoes, in particular, cluster toward the upper end of the acidity spectrum—all 10 of the most acidic tomatoes are, in fact, cherries.

This inverse relationship between fruit size and the concentration of sugars and organic acids has been observed in tomato research for decades. The exact reason isn’t entirely clear. It may partly reflect a dilution effect, where larger fruits accumulate more water relative to flavor compounds. It may also be an unintentional consequence of breeding for larger fruit size, which can indirectly shift the balance of sugars and acids in the fruit.

Interestingly, this trend isn’t unique to this dataset. Earlier USDA research investigating tomato acidity in the 1970s observed a similar pattern, with cherry-type tomatoes averaging slightly lower pH (and therefore higher acidity) than larger fruit types.

For gardeners hoping to grow tomatoes that are a little easier on the stomach, this suggests a simple starting point. While there are always exceptions, larger slicing tomatoes are statistically more likely to fall on the lower end of the acidity spectrum than tiny cherries or currant tomatoes.

So if color doesn’t reliably predict acidity—but fruit size often does—the next question becomes clear:

Which varieties actually contain the least acid?

While it wasn't the least acidic tomato in the study, Big Rainbow earns its low-acid reputation, coming in 28% in lower than the average tomato in the study.

The Tomato Varieties with the Lowest Measured Acidity

While the overall pH range of tomatoes is fairly narrow, the amount of organic acids present in the fruit can vary substantially between varieties.

Using the adjusted means calculated from the multi-location trial data, I ranked all 154 varieties in the study by their total concentration of malic and citric acids. The fifteen varieties below represent the lowest 10% of tomatoes tested.

The difference between the most acidic and least acidic tomatoes in the dataset is striking. The lowest-acid varieties contain roughly 40% less total acid than the average tomato in the study, demonstrating that meaningful differences between varieties do exist—even within the relatively tight pH range typical of tomatoes.

An Interesting Observation:

Two of the varieties at the very bottom of the acidity scale are particularly interesting from a historical perspective. Zapotec, a deeply ribbed tomato traditionally grown by indigenous farmers in Oaxaca, and Livingston’s Paragon, one of the oldest named tomato varieties still in circulation, both appear among the least acidic tomatoes in the entire dataset.

Their presence highlights an important point: low-acid tomatoes are not a modern invention. If anything, these results suggest that the genetic diversity for lower acidity has existed in tomatoes for a very long time.

For gardeners looking to grow tomatoes that may be a little easier on the stomach, these varieties offer a good place to start.

Other Relatively Low-Acid Tomatoes

While the varieties listed above fall in the lowest 10% for acidity, many other tomatoes also contain less acid than the study average. In fact, a number of well-known heirlooms fall comfortably into this lower-acidity group.

Collectively, the varieties below contain about 25% less total acid than the average tomato in the study. Because the full list is quite long, I filtered it to include well-known varieties that are readily available from commercial seed companies or through Seed Savers Exchange.

• Big Rainbow
• Cherokee Purple
• Moneymaker
• Old German
• Orange Strawberry
• Ponderosa Pink
• Soldacki
• Watermelon Beefsteak

While these varieties are not the lowest-acid tomatoes identified in the study, they still contain noticeably less acid than average and help demonstrate the wide natural variation in acidity that exists among tomato varieties.

Other Factors That Can Influence Heartburn

Choosing a tomato variety with lower measured acidity may help some people enjoy tomatoes more comfortably, but tomato chemistry is only part of the story.

Heartburn and indigestion are influenced by many factors, including portion size, meal composition, and individual sensitivity. Tomatoes are often eaten alongside foods that can also trigger reflux—such as fatty, fried, or spicy dishes—so the tomato itself may not always be the sole cause.

What the data does show is that not all tomatoes are chemically identical. While tomatoes tend to fall within a narrow pH range, the actual concentration of organic acids can vary substantially between varieties.

For gardeners who find tomatoes hard on the stomach, choosing varieties that fall toward the lower end of the acidity spectrum may make them easier to enjoy.

The least acidic tomatoes aren't always what you'd expect. Costoluto Genovese, an Italian sauce tomato, was among the least acidic tomatoes in the study.

Final Thoughts

For years, gardeners and cooks have debated whether low-acid tomatoes really exist. The research suggests that the answer is both yes and no.

Tomatoes generally fall within a fairly narrow pH range, which is why they remain safely acidic for home canning regardless of variety. But when scientists measure the actual organic acids inside the fruit, meaningful differences between tomatoes do emerge.

Some varieties contain substantially less acid than others, and broader patterns—such as fruit size—help explain where those differences tend to occur. While no tomato can truly be called “acid-free,” the data show that variety choice can influence how much acid ends up in the fruit.

For gardeners who find tomatoes a little hard on the stomach, starting with larger-fruited varieties and those that fall toward the lower end of the acidity spectrum may make them easier to enjoy.

Want to try for yourself? Our collection of low acid tomatoes features the varieties that have been demonstrated, from this study and others, to actually contain less acid.

Resources and Methods

Tieman, D., Bliss, P., McIntyre, L. M., Blandon-Ubeda, A., Bies, D., Odabasi, A. Z., Rodríguez, G. R., van der Knaap, E., Taylor, M. G., Goulet, C., Mageroy, M. H., Snyder, D. J., Colquhoun, T., Moskowitz, H., Clark, D. G., Sims, C., Bartoshuk, L., & Klee, H. J. (2012). The chemical interactions underlying tomato flavor preferences. Current biology : CB, 22(11), 1035–1039. https://doi.org/10.1016/j.cub.2012.04.016

Calculation of adjusted means:  

Adjusted means for each tomato variety were calculated in R using linear modeling to account for variation across experimental conditions. Acid measurements were modeled as a function of variety, with additional factors (e.g., location, year) included to control for background variability. Estimated marginal means (also referred to as least-squares means) were then computed for each variety, providing values adjusted to a common baseline across the dataset.

All analyses were performed in R (R Core Team), and adjusted means were generated using the emmeans package. These values were used for comparisons among varieties and for summarizing differences in acidity across color groups and fruit sizes.