Sugars & Brix • Starch, Dry Matter & Dry Weight • Pollination & Fruit Set • Fruit Maturity & Seed Maturity
A winter squash or edible pumpkin should have a delicious, sweet flavor and smooth, pleasantly dry texture when cooked. All too often, a supermarket squash will fall short of this standard, and taste flat, watery, or simply boring. Dr. Brent Loy, a cucurbit breeder at the University of New Hampshire, describes this problem as "a grower's paradox."
Several factors determine the eating quality of winter squash and pumpkins, but these factors are not always compatible with maximum profits. This is especially problematic for wholesale growers, who have little incentive to go the extra mile to deliver great-tasting squash. Direct-market growers, on the other hand, are in a position to produce the highest quality squash, and to offer it at a premium. And home gardeners certainly can choose to grow and enjoy the finest winter cucurbit varieties.
To achieve this goal, it helps to understand some of the dynamics at play between yield and eating quality, as well as a few key points concerning harvesting and storage. If growing great-tasting squash and pumpkins is your goal, you will want to read Dr. Loy's recommendations for superior eating quality.
Good eating quality is determined mainly by the percentage of sugars and starch in the edible portion of the squash.
- Brix. Degrees Brix (symbol °Bx) can be used as an indicator of vegetable or fruit quality as a function of the sugars present in it. One degree Brix is equivalent to 1 gram of sucrose in 100 grams of solution. In winter squash it is positively correlated with eating quality.
- Dry matter. Dry matter, also known as dry weight, is a measurement of the mass of a fruit or vegetable when completely dried, ie, all of its solid constituents. In winter squash it is positively correlated with eating quality and negatively correlated with yield.
Dr. Loy distinguishes the two:
Sugars: "High sugars not only contribute to a desirable sweet taste, but also mask undesirable flavor components associated with certain varieties. Sugar levels can be estimated easily by pressing juice from a small sample of flesh and measuring soluble solids in the juice with a hand-held refractometer. Relative sugar content is given in units of percent soluble solids (or degrees Brix). Soluble solids levels of 10% are passable, but generally levels of 11% or greater are considered necessary for good eating quality in squash."
Starch: "The pasty texture of squash is attributable to starch. At harvest, starch comprises about two-thirds of the dry matter of squash, so squash with high dry matter also have high starch content. Starch provides substrate for conversion to sugars during the latter stages of squash maturation and during subsequent storage. Squash with low dry matter, generally less than 16%, lack sufficient starch levels to produce the combination of pasty texture and degree of sweetness desired for acceptable eating quality. In varieties with low dry matter, starch is rapidly depleted during storage by conversion to sugars, and the texture of the squash becomes watery and fibrous."
What this means is that squash with higher dry matter content will hold its flavor better over time. Dry matter content is largely determined by variety. The "grower's paradox" referred to by Dr. Loy arises because a higher percentage of dry matter means a lower fresh-weight yield. As a rule of thumb, a variety with an excellent level of dry matter, say 20%, will yield considerably less than a variety with 10% dry matter. Simply put, higher-quality squash varieties typically yield less than lower-quality varieties.
"A grower interested in marketing the best-quality winter squash must often sacrifice fresh weight yield," Dr. Loy writes. "This is less of a problem at a retail market because a grower can highlight a quality product and price accordingly, but with lack of quality control for squash in supermarkets, a wholesale grower has little incentive to plant a variety which has the best eating quality."
Another critical factor in eating quality is maturity of the squash at harvest.
Most small varieties reach full size by 20 days after fruit set. Accumulation of dry matter and starch content peaks at 30 to 35 days after pollination. However, the fruit is not mature until the seeds are fully developed, which occurs at about 55 days after fruit set.
Dr. Loy stresses the importance of maintaining healthy plants until at least 50 days after fruit set, because photosynthesis is essential to the development of sugars and dry matter. A squash that is picked too early will continue to develop seeds, but it does so by depleting the dry matter, thereby reducing eating quality.
Although fruit and seed maturity are similar across the three main species of edible winter squashes and pumpkins, harvest and storage recommendations vary by type.
What happens to squash fruits in storage?
At harvest, before storage, the flesh of most kinds of winter squash is dry and not very sweet. Over time, in storage, some of the flesh's complex starch (dry matter) breaks down into simple sugars and water. The result is squash with improved flavor — a sweeter and pleasantly moister taste. There is an optimal storage period, differing for each type of squash; after that, fruits may appear to be storing well, but usually the flavor will decline.
Cucurbita maxima • Kabocha, Hubbard & Buttercup Squashes
Kabocha, hubbard, and buttercup (C. maxima) varieties should be harvested before complete seed maturation, at about 40 to 45 days after fruit set, when the fruit is still bright green (before the color fades). That's when the rind is hardest, so less likely to be damaged in storage. They also are susceptible to sunburn as the vines die down, so it's best to get them harvested and out of direct sun before then, to prevent the rind from turning brown or, with extreme sunburn, white.
Kabocha squash have high dry matter content and a small seed cavity, so seed maturation off the vine is not a problem. Store kabocha fruits for a month or so before eating.
C. pepo • Acorn Squash, most Pie Pumpkins
Acorn squash (C. pepo) can be misleading because they reach full size and develop a dark green-to-black mature color about two weeks after fruit set — 40 to 50 days before they should be harvested. Dr. Loy says that a better way to judge maturity is to look at the rind where it touches the ground. Immature squash have a light green or light yellow ground color, whereas mature squash have a dark orange ground color.
Immature acorn squash have low sugar levels, and although they will develop sweetness after harvest, they do so by depleting the dry starchy matter to convert it to sugars. This means storage life is shortened and eating quality declines.
C. moschata • Butternut Squash, some Pie Pumpkins
Butternut squash (C. moschata) are easier to judge by sight because they don't acquire their characteristic tan color until late in development, 35 days or more after fruit set. If the weather stays frost-free, they should be allowed to remain on the plants until 55 days after fruit set, then stored for a month or so before eating.
Besides sweetness increasing in storage, carotenoid content also increases, making butternut squash more nutritious after it's been stored for a couple of months. To accelerate maturity and increase sweetness, Dr. Loy has found that butternuts held at warm temperatures (up to 85°F/29°C) for two weeks after harvest develop acceptable enough levels of sugars for good eating.
Store winter squash and pumpkin fruits at 55–60°F/12–16°C, with relative humidity between 40% and 60%. Maintain good air circulation. Sort through stored fruits biweekly and remove any that are beginning to rot.
To grow the best-tasting winter squash…
- Look first for varieties renowned more for flavor than yield — the fact that all of our winter squashes have been bred or selected for the best taste is what makes them stand out.
- Don't harvest them too early, and keep them in storage long enough for the sugars to reach acceptable levels, but not so long that flavor deteriorates.
- Calculate the scheduling of each type of squash before you decide which ones to grow, matching peak flavor to the duration of your markets in fall and winter. It would be pointless to have bins full of butternut or grey kabocha squash reaching their best eating quality after your markets close. You would be better off growing larger quantities of varieties that reach maximal flavor during your busy selling season.
By following these guidelines, you should be able to produce winter squash and edible pumpkins with excellent eating quality. If you're a market grower, once your customers realize how great a winter squash can taste, they will look forward to buying from you every fall; if you're a home gardener, you, too, are sure to develop a loyal following.