Learn the science behind:
Have you ever considered making a cake using Brussel sprouts puree? Or a creamy sweet pie using broccoli? Probably not, but chances are you’ve seen or made something like it, but using another vegetable: pumpkins!
Pumpkins work great in lots of dishes, whether it’s pies, cakes, breads, or pancakes. For most of these applications, you’ll use pumpkin puree. Pumpkin puree is smooth and creamy, unlike purees you’d make from most other vegetables.
The ‘secret weapons’ hiding in a pumpkin? Starches and pectins!
- The composition of a pumpkin
- How to make pumpkin puree
- Benefits of using pumpkin puree in baked goods
- Fixing a pumpkin puree
The composition of a pumpkin
There are a lot of different varieties of pumpkins. They differ in color, size, flavor, water content, and more. All these pumpkins consist of mostly water, and barely any fat or proteins. Instead, most of the pumpkin that’s not water, is made up of carbohydrates. Still, that means carbohydrates make up less than 10% of a pumpkin.
Carbohydrates is the common name for a large group of molecules with a very similar structure. In pumpkins, the most common carbohydrate is starch, making up about half of the carbohydrates. Pumpkins also contain a reasonable amount of sugar, a smaller carbohydrates. When it comes to sugars especially, quantities can vary widely between varieties but even between different individual pumpkins. The rest of the carbohydrates consist of larger carbohydrates that are responsible for a pumpkin’s structure, such as celluloses, hemicelluloses, lignin, β-glucans, and pectins.
So why would you want to know what a pumpkin is made of? Because it explains just why a pumpkin makes a nice puree, unlike a celery stalk or carrot.
Asides from pumpkins, potatoes and legumes are probably one of the most pureed plants in our worldwide cuisines. They all have in common that they contain a good amount of starch. Starches can absorb and hold onto water very well, especially when they’ve been heated. It’s why even a watery product such as a potato or a pumpkin can still give a firm puree. And, it explains why an ingredient such as potato starch is used in baking quite regularly.
Pumpkin starches are a little different from the most commonly known starches such as those from potato and corn. Pumpkin doesn’t have as much starch as a potato does, so the final puree tends to be a little softer than one made from a potato.
Pectins form gels
Pumpkins consist of approximately 1% pectins. Pectins are large molecules that can bind water well and form a gel-like texture. They’re crucial for making fruit jams and why they can be used to make gummies.
Pumpkin contains a type of pectin that forms a gel-like structure quite easily. Only a small concentration is required to make a gel. It will also help to hold on to moisture, making it less dry (which is often a risk when using no or limited fat). Pumpkin pectin specifically is known to be able to form soft gels at quite low concentrations. Hence it’s perfectly suited to making a pumpkin pie!
No structural problems
Another reason pumpkins are great for being made into a puree is that there aren’t any ‘structural challenges’. A pumpkin might have a hard, firm outer layer, but the inside is quite soft. It doesn’t contain an awful lot of fibruous molecules such as lignins and cellulose. And that’s a good thing when making a puree. These molecules don’t tend to break down as well and wouldn’t give as smooth a puree.
To illustarte let’s have a look at a product on the opposite end of the spectrum: celery stalks. These stalks won’t make a smooth puree due to its low starch and pectin content and high amount of molecules such as cellulose which are responsible for the fibrous structures.
How to make pumpkin puree
So starches, pectins and the lack of very fibrous structures make pumpkins well suited for being made into a puree. How do we go about it?
Step 1: Cutting the pumpkin
The hardest part of making a pumpkin puree is often the cutting of the pumpkin! The hard outer layer can make it tough to break a pumpkin down into smaller pieces. But, it’s the starting point of making most purees and once that’s done, the hard work is over.
For some pumpkins you’ll need to remove this hard outer layer. However, others will soften as you heat them and you can leave them on. As an example, you don’t have to remove the skin from a butternut squash, but a sugar pumpkin is best when peeled.
Step 2: Heating the pumpkin
Sign up to our weekly newsletter to be updated on new food science articles.
Pumpkin, just like any other plant, is made up of plant cells. These are what give it its firm texture. To make a puree, you need to break down these cells. That’s best done with heat. Heat causes cell walls to soften and collapse and makes the pumpkin considerably softer. You have several options to do so.
Oven heats, dries & adds flavor
Pumpkins contain a lot of water and some varieties even more than others. If you have a particularly moist, slightly bland pumpkin, you might want to get rid of some of that water. It will make the final puree thicker. This is where roasting pieces of pumpkin in the oven might be the best solution. The oven will dry the outside of the pieces of pumpkin, while slowly heating and softening the pieces as a whole. As an added bonus, the outside of the pumpkin may turn brown and develop some delicious flavor thanks to the Maillard reaction.
Want to evaporate extra moisture? Cut the pumpkin into smaller pieces. The smaller the pieces, the easier moisture evaporates.
Stovetop softens quickly
Roasting in the oven does tend to take a little while. If you’re looking for a faster solution and have a firmer, less moist pumpkin at hand, you can also consider using the stovetop. It’s the method we use in the recipe below.
In this method you’ll simply heat the pumpkin in the pot with a little water. The water serves to prevent the pumpkin from sticking to the bottom, but does make the overall puree a little more moist. The advantage of using water and a closed pot is that it softens considerably faster than in the oven.
Step 3: Puree & Grind
Once a pumpkin has been heated through and softened completely, it’s a matter of breaking down those final structures to create a complete smooth experience. From here on, it’s simple, use a masher, food processor, fork, spoon or whatever device you have at hand to soften it all.
Original pumpkin purees use original pumpkin varieties
Even though most recipes and instructions will call for just a select vairety of pumpkins, there are actually a lot of other options!
One that works well for making a pumpkin puree is the blue/green kabocha. It’s a creamy and soft pumpkin. The green skin becomes soft easily and the inside is starchy and dry, giving a firm puree.
Benefits of using pumpkin puree in baked goods
Aside from giving a smooth and creamy texture to a puree or pie, there can be many more reasons for adding pumpkin. Admittedly, adding flavor is often not one of them. A lot, though not all, pumpkins are quite bland in flavor, but do carry other flavors, such as spices, very well. Pumpkins do add color to your product, as we saw with our pumpkin pancakes. And pumpkins can add extra fibers to a baked good.
Pumpkin puree as a fat replacer
Interestingly, researchers have studied pumpkin purees for use as a fat replacer. It isn’t easy to replicate the smooth, creamy texture that fats add to a product, it’s what sets an enriched bread apart from a regular brown bread. But, pumpkin puree seems to be a decent alternative. Adding pumpkin helps prevent a bread or cake from turning dry prematurely. It also adds some richness and velvetyness!
Fixing a pumpkin puree
This is hard to fix once the puree is made, but, you can try to spread it out on a tray and dry it on a low heat in the oven.
Next time you’re making a puree from a similar style pumpkin, try the oven roasting method. If you already did, you might want to use a different variety.
That’s an easy fix! Just add a little water until you have the right consistency. Keep in mind that every pumpkin is a little different and will give a different puree. So, it’s better to err on the dry side and add water later than the other way around.
Remember all those different types of pumpkin? And remember how even within a single variety there can be a lot of variation? Well, manufacturers solve this by making big batches with a lot of pumpkins, often mixing varieties. This way, they can also get the same consistency.
Bakirci, S., Dagdemir, E., Boran, O.S. and Hayaloglu, A.A. (2017), The effect of pumpkin fibre on quality and storage stability of reduced-fat set-type yogurt. Int J Food Sci Technol, 52: 180-187. https://doi.org/10.1111/ijfs.13264
Jurgita Kulaitienė, Elvyra Jarienė, Honorata Danilčenko, Judita Černiauskienė, Agata Wawrzyniak, Jadwiga Hamulka and Edita Juknevičienė, Chemical composition of pumpkin (Cucurbita maxima D.) flesh flours used for food, Journal of Food, Agriculture & Environment Vol.12 (3&4): 61-64. 201, link
Nataliya M., PtitchkinaIrina A., Danilova, Georgios Doxastakis, Stefan Kasapis, Edwin R.Morris, Pumpkin pectin: gel formation at unusually low concentrations, Carbohydrate Polymers, Volume 23, Issue 4, 1994, Pages 265-273, link
Smith, Desiree, Baking Alternatives – Reducing Fat in Your Favorite Baked Goods Recipes, Apr 19, 2010, link
USDA, Food Data Central: pumpkin, raw, FDC ID: 168448, link
Sang-Ho Yoo, et al. “Structural Characteristics of Pumpkin Pectin Extracted by Microwave Heating.” Journal of food science, v. 77 ,.11 pp. C1169. doi: 10.1111/j.1750-3841.2012.02960.x