How can genetic engineering produce tomatoes that are ripe when they reach consumers?

Answer 1

"Normally" tomatoes soften as they ripen, so they are usually picked green and shipped in that unripe state so they will stay firm. Just before delivery to the consumer these tomatoes are forced to ripen by gassing with the plant hormone ethylene gas. The consumer gets firm, ripe tomatoes (but less than fully sweet). These tomatoes will soften.

Using genetic engineering you can delete or disable the gene for the enzyme that causes the tomatoes to soften as they ripen, so they can be allowed to fully ripen on the vine (and become fully sweet) before they are picked and shipped. The consumer gets firm, ripe, and sweet tomatoes. These tomatoes will remain firm.