The nutritional wealth and health benefits, the perfect balance between sweet and sour, and why we are wrong when we think of it as a fruit. The Science of Strawberries
Winter is already around the corner and the markets will soon become filled with the red delicacy called strawberries. Its unique scent, flavor and aroma made the strawberry one of the most popular fruits in the world.
The strawberries we are familiar with are a breeding product of a cross between several varieties of wild strawberries, initiated in the 18th century. What is it about the color, flavor and scent of strawberries that entices us so much? Which is better - large or small berries? And the biggest question of all: how do you prevent them from going bad so quickly? We will look into each of these questions, but first we will offer of a recipe from the Italian cuisine - a strawberry crostata.
What do you need?
1¼ cups flour (180 grams)
½ teaspoon salt
1 teaspoon sugar
½ cup cold unsalted butter, cut into cubes (100 grams)
2-4 tablespoons ice water
¼ cup strawberry jam
2 ½ cups clean sliced strawberries
2 tablespoons sugar
1 tablespoon cornstarch
1 tablespoon milk or heavy cream
What do you do?
To prepare the crust, mix together the flour, salt and sugar, using a food processor or a mixer. Add the butter cubes and mix for another 10 seconds, until it coarse crumbs form
Continue mixing and immediately add two tablespoons of ice cold water. If the dough did not come together into a single large lump, add another tablespoon of water, and another one, if necessary. The stirring should not last more than 30 seconds.
Cover the dough with plastic wrap and flatten it slightly, to form a thick disc shape. Chill in the refrigerator for at least an hour.
Place the dough on a floured surface and sprinkle it with flour. Roll out the dough in one direction, lift it and turn it a quarter spin. Continue to roll it out in this manner until you have a circle of dough that is 1cm thick, with a 30cm diameter. If the dough sticks to the surface, slightly flour the work surface.
Transfer the dough to a tray lined with a baking sheet and chill the refrigerator for 15 minutes.
To prepare the filling, heat the jam slightly in a small cup, for 10 seconds using a microwave. Mix well. Brush the dough with half of the amount of jam, leaving a 2 cm margin of uncovered dough on the periphery.
Arrange strawberry slices on top of the jam and brush them with the rest of the jam. Mix a tablespoon of sugar with cornstarch and sprinkle over the strawberry slices.
Fold the edges of the dough, such that they cover the strawberry slices around the edges. Brush the dough edges with milk and evenly cover them with the remaining sugar.
In an oven preheated to 180℃, bake for 30-35 minutes or until the dough turns golden brown and the strawberries soften. Let cool for 30 minutes before cutting and serving.
Serve with whipped cream or ice cream
A recipe from the Italian Cuisine - Strawberry Crostata. Rolled out dough and strawberries | Shutterstock, taranova oxana
And Now to the Science
Botanists refer to strawberries as an accessory fruit. Botanically speaking, strawberries are in fact a swelling of the receptacle that covers the ovaries of the flower, upon which the true fruits of the strawberries - the tiny green or brown bumps called “achenes” - develop. Each “fruit” (achene) is in fact one of the flower’s ovaries, with a seed inside. This means that the red, fleshy part is the receptacle on which the flowers of the strawberry grow, and on which the fruits later develop, similar in a way to clusters of grapes that develop on the vines. Thanks to this formation, strawberries are rich in fiber and also contain large amounts of vitamin C.
What endows strawberries with their bold red color are anthocyanins - a large group of water soluble pigments that are found in plant cells. This group includes hundreds of different substances that range in color from red to blue. The colors of flowers, fruits or leaves in nature are, to a significant extent, determined by the combination of different anthocyanin molecules found within them. Due to their sensitivity to acids, they tend to change their color according to their environment: in a neutral environment they will be purple, in an alkaline environment they will turn blue, while a highly acidic environment will make them turn red. Anthocyanin are also very potent antioxidants, and may confer quite a few health benefits to strawberries.
On Flavor and Size
The flavor of strawberries is determined by the right combination of sweet and sour. The flavor depends upon the balance between multiple substances. A ripe strawberry is composed of 90% water and the rest is mainly glucose, fructose (fruit sugar) and additional sugars. When the strawberries ripen, their sugar content goes from about 5% in the green immature fruit to about 6-9%, post ripening. The acidity mainly stems from citric acid, which is naturally present in strawberries. When the strawberries ripen, the acidity diminishes, and alongside the increase in sugar content, the fruit becomes sweeter.
The ripening process is greatly affected by the hormone Auxin. Its levels in the strawberries rise gradually and when it peaks the fruit starts to break down its cell walls. As a result, the ripe strawberry becomes juicy, sweeter and softer, compared to the stiff immature fruit. The intense scent of strawberries stems from a few of the hundreds of volatile molecules that are present in it.
When selecting strawberries, size does count. The larger and redder berries attract the eye, but they are usually relatively bland. The small berries are actually packed full of sweetness. Starting from the mid 18th century, strawberries went through artificial domestication and selection processes that changed their qualities. Among other things, strawberries became increasingly bigger, but not uniformly - their water content rose more than their flavor substances and their taste diminished. Smaller strawberries contain less water but a similar amount of flavor substances compared to the large berries, and thus their flavor is more pronounced. Farmers are the ones who prefer larger strawberries, as they are easier to pick and preserve better while transported.
The smaller berries are in fact packed full of sweetness. A woman applying sugar water on a strawberry pie | Shutterstock, Mikhaylovskiy
How do you Prevent Strawberries From Going Bad?
Similar to other organisms, strawberries are made of cells. A cell includes an outer shell that holds the cell’s liquid content, and inside it it contains a variety of molecules and organelles that are responsible for the cell’s proper functioning. One of the organelles that is unique to plants is the vacuole - a liquid reservoir that takes up most of the cell's volume, and is in charge of balancing the cell’s water content.
The vacuole has a variety of roles in the cell. One of these is regulating the pressure (termed Turgor pressure) that the cell’s liquid content applies to the cell wall, and that determines how tough the fruit or vegetable is. For example, in a fresh and crispy lettuce leaf, the vacuole is filled with liquids and thus it presses against the cell wall and toughens it. When the vacuole loses liquids, the lettuce’s cells lose their volume and toughness and the leaf becomes wilted and soft. The same happens in fruits: when the fruit’s cells are harmed, water leaks out and the Turgor pressure decreases. The result is that the fruit loses its firmness and becomes soft.
Strawberries, as mentioned, are accessory fruits. During ripening, the cells inside the strawberry expand and the shape of the strawberries is maintained by the pressure of the cell’s content that presses each cell against its neighbors. When this pressure is released due to loss of liquid, the fruit’s structure is weakened and it becomes soft and mushy. For the same reason it is unrecommended to freeze strawberries - the freezing process punctures the cell wall, and upon thawing the strawberry loses some of its liquids.
A similar process occurs when strawberries are damaged for other reasons. When cells are injured, microorganisms such as fungi and bacteria consume the sugar that is released from them. Similar to many other fruits, strawberries are acidic, thus bacteria cannot develop in the damaged cells but molds thrive in them. A small wound to the strawberry is enough to allow for the development of mold and the spread of rot in the strawberry.
Storage under proper conditions can slow down the process. It is important to make sure not to cram too many strawberries in a small package, to prevent them from squishing, but also don’t spread them out too far so that they collide with each other while the shopping basket is carried around. Temperature is also important. Since the strawberry’s ripening process starts when it is picked, it is important to keep them chilled to slow down their water loss. A low temperature will also slow down the proliferation rate of the microorganisms that constitute the reason for rotting of the fruit. Cutting the strawberries also shortens their shelf life, so you should only cut them right before use. This way their texture is preserved for a longer time.
All that remains is to select the (smaller) strawberries, have them fresh or baked and enjoy the flavor and aroma of red strawberries.