Zucchini and summer squash are usually slightly sweet. Flavor is not a major quality concern. Very rarely a squash fruit will be so bitter it is not edible and might cause medical problems. The bitter compounds are tetracyclic triterpenes called cucurbitacins. Although the reason for this occasional bitter squash is not definitely known, it has been proposed that it is due to rare cross-pollination with a bitter-fruited cucurbit during seed production, and subsequent planting and growth of a seed with the genes for bitterness. Contrary to what is sometimes thought, cross pollination of a zucchini or squash plant with a gourd plant will not cause the harvested zucchini or squash to be bitter.

Zucchini and summer squash for commercial market are harvested as immature fruit, while the skin and seeds are tender and the flesh is firm. Overmature squash with tough skin or seeds and pithy flesh is unacceptable

Zucchini squash varieties vary in color from light to very dark green. In the Eastern U.S. the market prefers light to medium green while the western market prefers medium to dark green. Yellow types of zucchini form a niche market. Yellow summer squash is usually a pale yellow that darkens as the squash fruit develops. Glossy skin indicates that the squash is not overmature.

Zucchinis will yellow more quickly if exposed to low levels of ethylene during storage.

The most desirable size for zucchini and summer squash will vary depending on the market, and may be specified to the nearest 1/4 inch. Whatever the desired dimension, uniform size is important for a high quality pack.

Squash fruit will grow more quickly when moisture is adequate and there are few fruit developing on the plant. Dry conditions and a heavy fruit load will slow the rate of growth.

Squash grows very quickly so harvest intervals should be timed to maximize the number of fruit of the desired size.

Zucchini should be straight and cylindrical with a slight taper towards the stem end. Yellow summer squash may be straight or curved, depending on the variety, with a larger blossom end. The crook-necked (curved) types are sold primarily in the Southeastern U.S. Misshapen squash may develop if pollination is inadequate. When pollination is incomplete the fruit develops unevenly because the ovary wall enlarges more adjacent to fertilized seed. One honey bee hive per one or two acres will help insure good pollination as long as male flowers are present. Sometimes female (pistillate) flowers open before male (staminate) flowers and there is little or no pollen available early in the season, resulting in poor pollination. This is more likely to occur with cool growing conditions.

Damage to Skin

Virus Diseases

Phytophthora

Summer squash and zucchini can be stored 1 to 2 weeks under optimum conditions.

Bruising the stem or fruit, or scraping the skin during harvest will promote decay and water loss and reduce shelf life. Squash stems should be cut cleanly from the vine.

Squash should be cooled rapidly after harvest to the proper storage temperature of 41˚F to 50˚F, and stored at 95% relative humidity. Waxes or oils applied to the squash can reduce water loss and help to maintain quality during storage. Temperatures below 41˚F cause chilling injury that reduces shelf life. Symptoms of chilling injury include water-soaked pitting and decay.