Pumpkin Puree – The science of pumpkins & pectin

All of a sudden, somewhere in September, supermarkets start filling up with pumpkins. The common orange, but also green, yellow and even blueish pumpkins. Pumpkins work great in a lot of dishes, whether it’s pies, cakes, breads, pancakes, soups or just roasted from the oven. Since pumpkins are quite big, it’s a good thing they can be used in so many different ways, else you’d never manage to finish it.

A lot of these applications, especially the baked goods, require the use of pumpkin puree. Potato puree is pretty common, but purees of other vegetables aren’t that common. A pumpkin though can make a super smooth, soft and even creamy puree. Just imagine trying to make a puree from Brussel sprouts or broccoli, chances are you won’t be successful.

But why does pumpkin make such a good puree? It so happens to be that pectins seem to play a role here.

An easy way to make pumpkin puree

Before diving into pumpkin puree science, let’s first discuss how to make pumpkin puree. A pumpkin puree is just a cooked and mashed bit of pumpkin. Pumpkin doesn’t have as much starch as a potato, so the final puree tends to be a little softer than a potato one. There are tons of ways to make a puree, each more complicated and elaborate than the other. However, making pumpkin puree can be super easy.

When making pumpkin puree all you have to do is to soften the pumpkin and blend or mash it. Especially if the puree is used in a cake or a bread (see a recipe at the bottom of this post), where you will probably not even recognize it, it’s best to just do this as easily as possible.

For this method to work you’ll need a pumpkin with a skin that isn’t too tough. Preferably you’re looking for a slightly thin skin. By using a thin skin pumpkin you generally don’t need to peel the pumpkin nor leave it to cook for very long. Cut the pumpkin in smaller (5x5cm) pieces and place them in a small pot on a low to medium heat. Add a thin layer of water, just enough for the pumpkin pieces not to stick to the bottom. Now take care to place the lid on the pot and leave to simmer gently. Gently poke and stir the pieces regularly. They should soften by themselves within about half an hour. Once you can smash them down with a wooden spoon it’s done, use a blender to soften it further.

pumpkin puree from the kabocha pumpkin

Choosing a pumpkin for puree – Kabocha

There are so many different types of pumpkins. They differ in colour, texture and definitely flavour. The more commonly used pumpkins are the orange sugar pumpkin and the butternut squash. They are often recommended for cooking with. However, there are so many other types!

One that will definitely work for making this pumpkin puree and this pumpkin bread at the bottom of this post is the green kabocha. It’s a creamy and soft pumpkin. This pumpkin can be made into a pumpkin puree super easy. The green skin becomes soft very easily. The pumpkin is pretty starchy and dry so it will give a dry pumpkin puree easily, without having to evaporate a lot of moisture.

Pumpkin puree as a fat replacer

Now that we’ve got that pumpkin puree it’s time to use it in our cooking. Puree is used in the ‘famous’ pumpkin pie of course where it serves as the filling of the pie, it has a central position. However, in a lot of other recipes such as pancakes, breads and muffins, pumpkin is just one of the ingredients in the batter.

If you’re honest, these baked goods often don’t really taste like pumpkin, maybe just faintly, as is the case for carrot cake. But then why add the pumpkin puree? Remember that zucchini chocolate cake though? In this cake you couldn’t taste the zucchini either but it did help to keep the cake moist and soft. Zucchini’s are actually a relative of pumpkins. In fact, pumpkins impact the structure of a cake similarly, it might even be better in doing so.

The baking industry has been looking for fat replacers in baked goods for quite a while. There is considerably research looking for such a replacer. This isn’t that easy. Fat contributes to the smoothness of your product and gives it a certain richness. Without fat a bread for instance will be a lot drier (see also enriched breads).

When looking for a fat replacer you’re looking for something that can make up for this loss of fat. Common examples are apple sauce or smashed bananas, as well as several other fruit purees. However, these might not be thick and rich enough to really serve as a proper substitute. Enter pumpkins.

Pumpkin pectin

 

Pumpkin contains a lot of pectins which are a type of polysaccharide. Pectins are large complex molecules. When making jams these pectins tend to play an important role. Thanks to the pectins the jam will thicken up well. Apple also contain this pectin which is why they’re often used in one way or the other in jams.

It so happens that pumpkin contains a type of pectin that forms a gel like structure quite easily. Only a small concentration is required to make a gel set. When adding pumpkin to a baked good these pectins will also help form such a gel like structure. This will enrich the structure of your cake or muffin. It will also help to hold on to moisture, making it less dry (which is often a risk when using no or limited fat). As a result, this pumpkin bread below can be made without adding any additional fats while it still tastes rich like a cake and definitely not dry.

 

pumpkin bread

 

Pumpkin Puree - The science of pumpkins & pectin
 
Prep time
Cook time
Total time
 
Author:
Recipe type: Cake
Serves: 20 slices
Ingredients
  • 250g flour
  • 1 tsp cinnamon
  • 1 tsp nutmeg
  • ½ tsp ginger
  • ⅛ tsp clove
  • 1 tsp baking powder
  • 1 tsp baking soda
  • 200g sugar
  • 225g pumpkin puree (see below)
  • 2 eggs
  • 250ml milk
  • 25g butter (melted)
  • 50g walnuts
  • 75g raisins
A suggestion for homemade pumpkin puree
  • Take a kobachu pumpkin and cut off a quarter of the pumpkin. Cut into smaller pieces.
  • Add in a pot with a little water and gently bring to the boil.
  • Cook until all the pumpkin has turned soft. You can leave in the skin.
  • Take a hand held blender to further break down the pumpkin and create a soft smooth puree.
Instructions
  1. Cover the raisins in water to hydrate them.
  2. Mix the flour with the spices, baking powder & soda and the sugar.
  3. Mix in the pumpkin puree and eggs with a spatula or stand mixer on a low speed.
  4. Add the milk and stir out the lumps.
  5. Pour the water off the raisins and remove any excess water.
  6. Mix the melted butter, walnuts and raisins through the batter gently.
  7. Cover a cake pan with baking paper and pour in the pumpkin bread batter.
  8. Bake in an pre-heated oven of 160C for 1h15min, or until a cake tester comes out clean. If the top turns too brown, cover with aluminium foil to prevent further browning.
  9. Leave to c

Resources

Structural characteristic of pumpkin pectin extracted by microwave heating, 2012, Sang-Ho Yoo et al., link

Scientific article investigating the extraction of pectins from pumpkin using microwaves

Scientific article on using pectin rich materials to replace fat in baked goods

Research investigating the use of applesauce as a fat replacer.

Use of pumpkin as a fat replacer in yogurt.

Graduation thesis on using pumpkin puree as a fat replacer in brownies and cupcakes.

Methods to reduce fat content in baked goods, an article by Wilton

Pumpkin pectin: gel formation at unusually low concentrations, 1994, link

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