Why Do Tomatoes Change Color as They Ripen? Tomatoes contain two
pigments for photosynthesis—chlorophyll, which is green, and
lycopene, which is red. When tomatoes start to grow, they
contain much less lycopene than chlorophyll, which gives them
their green color. But when harvest season arrives, the days
shorten and temperatures drop, causing chlorophyll to dissolve
and lycopene to take over the shade of the fruit. During this
time, sugar levels rise, acid levels drop, and the tomato
softens. It becomes ready to eat. The trick is that this final
stage of a tomato’s life takes place in a relatively short
period of time—and that poses a big problem for farmers trying
to get ripe produce to grocery stores before it rots. Most
farmers begin picking tomatoes while they’re still green on the
vine, and then they treat them with a ripening agent called
ethylene gas to induce the red color. Far from being a synthetic
compound, ethylene gas is produced naturally by other fruits and
vegetables as they ripen. In fact, b