Were the strawberries you harvested a bit too sour? It’s unfortunate but non-climacteric fruits such as strawberries, grapes, and raspberries, among others, do not ripen further after harvesting. However, what if we tell you there are ways to accelerate the ripening process before and after harvest?
Ripening in strawberries before harvesting can be accelerated through 1) warmer temperatures, 2) increased concentrations of potassium and phosphorus nutrients, and 3) sucrose solution treatments. After harvesting, ripening can be “forced” by 4) enclosing strawberries with fruits that produce ethylene such as bananas or apples.
Different fruits have different rates of ripening before and after harvest and the humble strawberry is no exception. It’s just how nature designed them. However, only a little bit of human ingenuity is needed to get around these restrictions.
Unlike other fruits, strawberries do not ripen after picking. Strawberries remain in the same state from the time they are picked.
Strawberries are classically non-climacteric fruits that do not ripen after harvesting. On the other hand, climacteric fruits continue to ripen after harvesting due to their receptivity to ethylene gas which signals ripening, causing fruits to become softer and sweeter.
Strawberry varieties are often ready for harvesting 4-6 weeks after blossoming – a process that arrives during the warmer seasons, from late spring to summer. It’s better to harvest the strawberries during these periods when they are fully red.
Fortunately, we can accelerate the ripening process before harvesting. Due to the non-climacteric nature of strawberries, harvesting at the right time is still essential but we can make the wait more bearable.
To speed up the ripening in strawberries, it is sufficient to increase the environmental temperature. This can accelerate the ripening by 30%.
A study conducted on blooming strawberry plants subjected to high-temperature (32.8°C/20.8°C) and low-temperature (20.8°C/12.°8C) treatments resulted in a 12-day difference in favor of the high-temperature treatment. The strawberry fruit had reached full maturity and ripeness in 24 days in high temperature compared to the 36 days in low temperature.
Gardeners living in colder climates may elect to put up a greenhouse or a greenhouse heater to keep their strawberry plants growing in a nice and warm environment.
Gardeners living in warmer climates such as the tropics may have a difficult time growing strawberry plants unless they are grown in high altitudes since strawberries plants survive in temperate climates. To emulate this climate, growing indoors or through an indoor hydroponic setup is preferable, only increasing the temperature when the plant starts blooming.
An abundance of the essential macronutrients nitrogen-phosphorus-potassium (NPK) has exhibited accelerated fruit formation and ripening in strawberry plants.
Specifically, a higher concentration of potassium and phosphorus is optimal for flowering and fruiting plants. Phosphorus is responsible for fruit formation and ripening whereas potassium promotes overall plant function. A lower concentration of nitrogen is optimal since enhanced leaf growth is not as desirable in flowering and fruiting plants.
Strawberry plants grow well under compost-rich soil so most organic fertilizers found in gardening stores will do the job. Chemical fertilizers are also an equally viable option.
Foliar sprays applied directly to the leaves and fruits can augment the fertilization process. The necessary nutrients can be mixed in a mister and applied liberally on the leaves and fruits of the strawberry plant.
In both applications, what is essential is that there is a higher concentration of potassium and phosphorus compared to nitrogen. It is also important not to apply too much nutrients to prevent nutrient burn.
Recent studies have speculated that applying sucrose solution on strawberry fruits can accelerate the ripening process. Sucrose is suggested to be a key signal in the regulation of strawberry ripening.
It was discovered that strawberry fruits sprayed with the sucrose solution treatment ripened to full red 4 days faster than those without the sucrose treatment. Additionally, RNA sequencing of the treated strawberry fruits are possibly more receptive to accelerated ripening through sucrose treatment. This means that seeds from these fruits may lead to strawberries which ripen earlier with successive treatments.
However, this process is still experimental so there is still room for discovery and experimentation. Scientifically-inclined gardeners may want to try this one out.
100 mM (millimoles) of a sucrose solution is sprayed at strawberry fruits when they are still young and dark green. Spray liberally until the strawberry fruits are dripping.
Note: Sucrose is sweet and sticky and will attract insects. Be careful in applying the solution outdoors as they may introduce pests to your garden.
Strawberries can be “forced” to ripen after harvest by enclosing them in a container like a paper bag with climacteric fruits. The climacteric fruits emit ethylene gas that creates an ethylene-rich environment which may force harvested strawberries to ripen as well.
Fleshy fruits such as bananas, avocados, tomatoes, and apples are classic examples of climacteric fruits that produce a burst of ethylene after harvesting.
Non-climacteric fruits’ ethylene production does not increase during ripening but they can be forced to ripen if exposed to an external ethylene source such as being in close proximity to climacteric fruits.
Simply place climacteric fruits together with strawberries in an enclosed container – a paper bag, a plastic Tupperware, a resealable plastic bag – at a room temperature of around 20-23°C (68-75°F). Leave the sealed container overnight.
You will observe that white or green-ish portions of the strawberry turn yellow or red, indicating ripening due to external ethylene produced by other fruits in the container. The strawberries may turn softer and sweeter as well. Leave them in the container with the climacteric fruit until the desired ripeness is achieved.
Note: Be diligent in not leaving the fruits in the container for too long. Overripening can lead some of the fruits to decay, affecting other fruits and spoiling the bunch. This is where the saying “one bad apple spoils the bunch” comes from!
Ethylene gas can be used to ripen strawberries as well as many other fruits. Ethylene is a “fruit-ripening hormone,” causing fruits to become softer and sweeter. All plants produce some amount of ethylene during their life cycle and this amount increases or decreases during particular circumstances in their life.
In nature, fruits ripen, becoming sweeter, more colorful, and more fragrant, to attract animals to animals to consume them. This allows the seeds to be transported and subsequently released in nutrient-rich excrement.
In industry, we have specifically-built ripening chambers regulating the amount of ethylene gas in a controlled environment. The ethylene gas is regulated to make sure that ripening is consistent and optimized for the needs of a specific fruit.
Though ripe strawberries are often associated with a vibrant red, new species of strawberries are being discovered and developed that can have different colors such as white.
Fragaria vesca is a wild strawberry plant that produces white fruit with scarlet seeds. On the other hand, Fragia nubicola, a strawberry plant native to the Himalayas can produce fruits that are either conventionally red or milky white.
Biologists have reported that they have sequenced the genome of such strawberry species to identify which genes are responsible for physical traits such as color and shape. Successive breeding may introduce strawberries that come in different colors, shapes, sizes, and flavor profiles in the market within 10 to 20 years.
Will Strawberries Ripen at Room Temperature?
Strawberries will not ripen at room temperature because they are still non-climacteric fruits. Leaving strawberries at room temperature will only speed up their decay.
There are some reports by gardeners that strawberries at room temperature or taken out of the fridge after 30 minutes to 1 hour are noticeably sweeter than refrigerated strawberries. This might be due to the decaying process that is returned to normal after taking the strawberries out of refrigeration.
- Strawberries are non-climacteric fruits that do not have a marked increase in ethylene gas that signals further ripening. Hence, strawberries remain in the same state of ripeness from the moment they are harvested.
- Ripening in strawberries before harvesting can be accelerated by subjecting it to 1) warmer temperatures, 2) increased concentrations of potassium and phosphorus nutrients, and 3) sucrose solution treatments.
- Ripening in strawberries after harvesting can be “forced” by enclosing them with climacteric fruits that have a marked increase in ethylene gas after harvesting. The external production of ethylene forces the strawberries to ripen, making them softer and sweeter in the process.
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