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Summer is zucchini time. And if you happen to be growing your own, you might well be faced with a zucchini overload. After zucchini soup, zucchini pastas, grilled zucchini salads, you might just start to run out of ideas. So why not mix it up, and make something completely different: a chocolate cake?!
Maybe surprisingly, zucchini works wonderfully well in all sorts of baked goods. It makes surprisingly moist and light products. Its high moisture content is a main driver for this, as is the fact that this moisture is “trapped”!
Zucchini is mostly water
Zucchini, as most vegetables, consists of mostly water. Well over 90% of a zucchini is water. The remainder is made up of some sugars and other carbohydrates such as some fibers, a little protein, several vitamins and minerals, and of course minor ingredients such as colors and flavors (source).
Cells hold onto the water
Despite being so much water, a zucchini is still quite firm. It’s not a liquid and doesn’t flow freely. This is because that water isn’t free. Instead, the water is held within the plant cells that make up a zucchini. Each plant cell contains a large ‘puddle’ of water. This water is held within the cell walls and cell membranes. Just like the zucchini itself, cells are made up of mostly water.
In a fresh firm zucchini, these cells are so full of water that the water presses against the wall. This causes the courgette to be firm. This phenomenon is called turgor.
Water can travel in and out of the cells, but only if the conditions permit it. In a dry environment, a zucchini will slowly dry out over time, water evaporates. This happens even more quickly if you cut a zucchini, causing cells to break and water to be set free.
Cooking causes water to be released
When you’re cooking a zucchini, the cells of the zucchini are broken down. The cell walls and cell membranes simply can’t withstand the heat. This causes the courgette to turn soft because the cells lose their turgor. Also, a lot of moisture seeps out. It’s why baked, fried, or grilled zucchini are all smaller in size than the original zucchini. It simply lost of lot of its contents. But, it doesn’t loose all! Some of it will remain within the cellular structure of the zucchini.
Baking with zucchini for moistness
So zucchini contains a lot of moisture, but, this moisture is not free to go, it’s trapped. This is a great advantage when you want to bake a moist cake. A moist cake needs enough water to remain moist. However, if you add too much liquid to a batter, it might become too thin and liquid. As a result, it might not cook through properly, or never fully rise.
Zucchini adds non-free water
It’s where the zucchini comes in. Yes, you add a lot of extra water. But, it doesn’t have as much of an impact on the texture of the batter. The batter still remains some of its thickness.
During baking, the zucchini does turn warm and lose some of its texture. As a result, some of the moisture does still escape the zucchini and become part of the cake. However, since this is a more gradual process, during baking, it doesn’t negatively impact the cake as much!
After baking a cake with finely grated zucchini, you’ll have a hard time finding the zucchini back. Only if you look very closely will you be able to see some green specks spread throughout.
Too coarse = too moist
In our cake comparison test we also tested two styles of zucchini grating. One zucchini we grated quite finely, whereas the other was grated very coarsely.
It was immediately clear the the coarsely grated zucchini did not work well in the recipe. It didn’t dissolve into the cake as much. As a matter of fact, this cake was too moist. Also, it didn’t have the structure that’s required of a cake. It collapsed slightly after baking and had several larger holes around the big pieces of zucchini.
Can zucchini replace eggs?
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In some recipes, zucchini can serve as a (partial) egg replacer. Often eggs are added to help with moistness. Zucchini can take of this role. However, as a we noticed, not all cakes can go without the eggs simply by adding zucchini. Our no-egg zucchini chocolate cake was by far the most moist cake of them all and had collapsed considerably. The eggs would have been necessary to help set the structure by the proteins denaturing in the oven.
Zucchini cakes remain fresh longer
We noticed that zucchini chocolate cakes could be stored in the fridge for several days without any major detrimental effects. The additional moistness makes it less prone to drying out. As a matter of fact, our no-zucchini sample started to turn dry within a day whereas the zucchini samples remained moist for days to come!
Samaa M. Saleh, Zucchini Puree as a Novel Egg Substitute in Cake: Comparing with Other Substitute, ALEXANDRIA SCIENCE EXCHANGE JOURNAL, VOL. 43, No.2. APRIL-JUNE 2022, link