Why Zucchini Works Great in Baking (+ Chocolate Zucchini Cake Recipe)

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.

Of course, zucchini isn’t the only vegetable that works great in baking. Pumpkin and carrots do too, to name just a few!

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?

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!

Zucchini chocolate cake

Yield: one 24cm cake

Prep Time: 30 minutes

Cook Time: 50 minutes

Total Time: 1 hour 20 minutes

Zucchini makes this chocolate cake moist and light. As a starting point, a Sally's baking addiction recipe was used.

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Ingredients

Cake

• 250g flour
• 65g cocoa powder
• 2 tsp baking soda
• 1/2 tsp baking powder
• 1/8 tsp salt (optional)
• 200g granulated sugar
• 190g butter (melted)
• 50g vegetable oil
• 4 eggs
• 80g plain yoghurt
• 2 tsp vanilla extract
• 600g zucchini

Frosting

• 100g butter (unsalted)*
• 100g icing sugar
• 35g cocoa powder
• pinch of salt
• 25g cream (or milk)*

Instructions

Cake

1. Line the bottom of a round 24 cm cake pan with parchment paper.
2. Mix together the flour, cocoa powder, baking soda & powder, salt and sugar. Whisk through.
3. Shred/grate the zucchini. Use a fine grater to do so (see below). A very coarsely grated zucchini makes the cake too moist. Do not shred these too far in advance, they'll start to loose moisture.
4. Add the melted butter, oil, eggs, yogurt and vanilla extract. Mix, it should come together quite easily.
5. Mix in the zucchini shreds.
6. Pour the batter into the cake pan.
7. Bake in a pre-heated oven at 180°C (355°F) for approx. 45 minutes, test the cake with a toothpick/tester, it should come out clean. This cake takes considerably longer to bake than a similar cake without the zucchini, so don't be surprised if it takes longer than you expect.

Frosting

Even though this cake has a great texture, the flavor is a little bland, so don't skip over the frosting, it really lifts the cake up!

1. Add all ingredients to a bowl and mix them together. The icing sugar may dust at the start, so start slowly and gently.
2. Mix until it is a homogeneous consistency.
3. Cool the cake down to room temperature. Do NOT attempt to frost the cake while it's warm. The frosting WILL melt.
4. Generously cover the cake with frosting.

Notes

*You can make the frosting without dairy by either using a plant-based milk or water instead of the cream and by replacing the butter with a plant-based alternative. Keep in mind that a lot of the texture and taste comes from the butter, so choose one that's soft at room temperature and has a nice taste and mouthfeel (not greasy).

References

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