4 types of red tomatoes and the tops stay yellow even when the the bottoms are dark red even to the point of rotting. August has been hot 86 to 95F, humid but not much rain. July was humid and rainy.
This one was left on till bottom started rotting.
It’s sun scald. If your tomatoes are anything like mine the lower foliage is dropping off and the fruit is getting a lot more sun exposure.
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Mine look the same.
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This is one case where tomatodirt is not quite right. Yellow shoulders are from sun bleaching which is a result of sun exposure… but!
The underlying reason is genetic. Tomatoes produce chlorophyll in the fruit which helps increase sugar levels. As they ripen, these fruit will retain green shoulders as the chlorophyll does not get converted to lycopene. This is very important for home growers. Tomatoes with green shoulders almost always taste better than fruits that ripen uniformly. Which gets us to:
There is a gene in tomato called “uniform ripening” that causes the fruit to turn red all over with no green shoulders. It has been a mainstay in tomato breeding until just a few years ago when someone asked why commercial tomatoes taste so bad. It turns out that uniform ripening inhibits chlorophyll in the fruit which prevents that extra bit of sweetness and flavor that tomatoes are supposed to have.
One other piece to this puzzle is needed if you want to grow the best flavored tomatoes. The biopath that produces most of the flavor in tomatoes is the carotenoid biopath. Yes, the biopath that makes tomatoes turn yellow, tangerine, red, or orange is the biopath that contributes most of the flavor compounds. Sugar is directly from chlorophyll but tomatoes vary in the amount of sugar they accumulate. The best flavored tomatoes will be the ones that turn the brightest color and accumulate relatively high levels of sugar. Caveat that there is a high lycopene gene that can actually make the flavor too intense in some varieties.
Lesson to learn? If you want good flavored tomatoes, get the ones that have green shoulders (can turn yellow in direct sunlight) and enjoy the tomato flavor. Slice the top of the tomato off and don’t eat it because it will have a slight off flavor compared to the rest of the fruit. Also, there are plenty of varieties that produce an abundance of foliage which tends to limit sun bleaching.
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