Supermarket tomato flavour

Why does a tomato bred by experts and grown at scale taste of so much less than one from a garden?

A tomato from a garden row and one from a supermarket shelf are the same species, and the second is the product of far more expertise, money and equipment. Yet the garden one tastes of something and the other mostly of wet. The convenient story is that somebody stopped caring. But nobody in that chain actually wants a bland tomato — the retailer would rather sell you a good one. So what were they optimising instead, and what did it cost without anyone deciding to spend it?

Ask first what a tomato is really graded on. Not by you at the table. By the grower paid per tonne, the packer whose fruit must survive a week in a box, the retailer whose display must look even and unblemished. The traits under selection, then, are yield, disease resistance, firmness, resistance to cracking and bruising, and uniform colour. Nobody in that chain is paid for flavour, and nothing measures it. A quality nobody scores does not stay put — it wanders.

But drift alone would only make flavour random, and this loss is systematic. So look for something stronger: a trait they selected for that removed flavour as a side effect.

There is a clean documented case. Older tomatoes ripen unevenly, keeping a dark green "shoulder" near the stem that colours last. Growers dislike this; you cannot judge a load at a glance. A mutation called uniform ripening abolishes it — the whole fruit is pale green and turns red evenly — and breeders adopted it almost universally through the twentieth century.

Now ask what the dark shoulder had been doing. It was dark because it was crowded with chloroplasts: the fruit was photosynthesising for itself. The uniform-ripening mutation turns out to disable a gene that builds exactly those chloroplasts. Remove it and you remove the fruit's own sugar-and-pigment workshop, and the mutant fruit carries measurably less sugar and less of the carotenoid stock from which several aroma compounds are made. The trait growers chose was not merely indifferent to flavour. It was the same gene.

Second thread. Where does a tomato's sugar come from? A little from the fruit, most of it shipped in from the leaves while the fruit hangs on the plant. Commercial tomatoes are picked mature-green and coloured downstream with ethylene gas. Ethylene will certainly make it red. It cannot make it sweeter, because the supply line was cut at harvest.

Third. What does the cold chain do? Tomatoes are chilling-sensitive. Held below roughly 12 degrees they largely stop producing their volatile aroma compounds — and, awkwardly, warming them again does not simply restore production; the machinery is suppressed, not paused. A week in a fridge is not a delay to flavour so much as a deletion of it.

Three independent mechanisms, all pointing the same way, none of them requiring anyone to say that less flavour would be acceptable.

Some refinements. Flavour here is not simply sugar. Tomato flavour rests on a couple of dozen volatile compounds, and some of them make a tomato read as sweeter at unchanged sugar. So flavour can be lost with the sugar figure barely moving — and modern varieties have indeed lost alleles for several of those volatiles.

It is also worth resisting the romantic version. "Heirloom" is not a quality grade: plenty of old varieties taste poor, and modern varieties bred with flavour as an explicit target taste very good. The claim is not that old is better. It is that flavour went unscored, and one heavily selected trait happened to be antagonistic to it.

And notice how much of the garden tomato's advantage has nothing to do with its genes: it was picked ripe, it never went below 12 degrees, and it was eaten within hours. Handle a commercial variety that way and a good share of the gap closes. That is the encouraging half of the story — some of the loss is written into the seed, but much of it is in the handling, and handling is cheap to change.

• How breeders are mapping volatile compounds to put flavour alleles back without surrendering yield.
• Why chilling injures some fruits and leaves others untouched.

Every term the collection defines is gathered in the glossary.