Rheology Meets Halloween: A Tale of Two Pumpkins

Every fall, we head to pumpkin patches searching for the perfect pumpkin. Some people pick the classic orange pumpkin. Others are drawn to the elegant white varieties.

As a rheologist, I couldn’t resist putting pumpkins to the test.

Instead of evaluating pumpkins by their shape, color, taste, or potential for becoming the neighborhood’s best jack-o’-lantern, I decided to investigate their mechanical properties. Would a white pumpkin be tougher to carve? Would an orange pumpkin make a better pie? Could rheology help explain what happens when pumpkins are heated in the oven?

Let’s find out.

To investigate, I compared both orange and white pumpkins, looking separately at the skin and the flesh.

The pumpkin skin was tested in two different ways:

• Shear rheology using an 8 mm parallel plate geometry on a Discovery HR 30 rheometer
• Linear rheology using a 10 mm Three-point bending clamp on a Discovery DMA 850

The smaller geometries helped minimize the effect of the natural curvature of the pumpkin skin, enabling more reliable mechanical measurements. Roughened 8 mm parallel plates were used to reduce sample slippage during testing. While shear rheological measurements are typically performed at a fixed gap, pumpkin skin thickness is not perfectly uniform. Therefore, a controlled axial force was applied to maintain consistent contact between the sample and the plates, ensuring accurate and reproducible measurements.

The white pumpkin consistently showed a higher modulus than the orange pumpkin. In simple terms, modulus is a measure of stiffness, so the white pumpkin skin resisted deformation more than the orange pumpkin skin (Figure 1).

The modulus measured in shear was lower than the modulus measured in bending for both pumpkins. That’s not unusual, since materials often resist bending differently than they resist shear deformation (Figure 2).

So while they may look similar sitting on your front porch, mechanically they are not identical.

Suddenly, those rheology results became very relatable.

Imagine carving a pumpkin on a chilly October evening.

A stiffer pumpkin skin can mean:

• More resistance when pushing a carving knife through the surface
• Cleaner cuts
• Better shape retention around detailed carvings

The softer orange pumpkin, on the other hand, may be slightly easier to penetrate but can flex a little more during carving.

So if you’ve ever felt that one pumpkin seemed to “fight back” while carving, rheology may have been the reason.

Before we declare a carving champion, however, there are two important caveats:

First, the modulus values for the two pumpkins were actually close. While the white pumpkin consistently came out slightly stiffer, the differences were not dramatic. Most pumpkin artists would probably do just fine with either variety.

Second, this study included two pumpkins from one local patch, so we should be careful not to overgeneralize. Factors such as soil composition, rainfall, sunlight, and growing conditions can all affect a pumpkin’s properties. While our white pumpkin won this particular stiffness contest, that doesn’t necessarily mean all white pumpkins are stiffer than all orange pumpkins.

Still, it’s fun to know that your pumpkin carving experience may have a scientific explanation.

Of course, pumpkins aren’t just for decoration. Eventually they find their way into soups, pies, breads, muffins, and nearly every autumn menu imaginable. So, I had to investigate the pumpkin flesh as well.

Using a DMA 850 equipped with a 15 mm compression clamp, I first identified the linear viscoelastic region (LVR) – the range where the flesh can be gently deformed without permanently changing its structure. Once that region was established, I performed an oscillatory temperature sweep within LVR to track how the pumpkin’s mechanical properties changed as it was heated, effectively giving the pumpkin a miniature “baking” experiment.

Based on the skin measurements, I expected the white pumpkin to be the stiffer of the two.

At lower temperatures, it was.

But as the temperature increased, the pumpkins had a surprise in store.

The orange pumpkin appeared to contain more available moisture (more watery) and showed a noticeable increase in stiffness as it approached 100°C.

That seems backwards. Shouldn’t heating make things softer?

Not always.

As moisture evaporates, the remaining structure becomes more concentrated, much like a simmering sauce that thickens as water cooks away. In other words, the watery pumpkin briefly gets tougher before it starts to break down.

As heating continued, a different process took over. Around 160°C, the orange pumpkin lost much of its original cellular structure, resulting in a dramatic drop in modulus.

The white pumpkin behaved quite differently. It showed neither the temporary stiffening near 100°C nor the sharp softening at higher temperatures, suggesting lower moisture content and better structural stability during heating.

If the orange pumpkin is the watery one, the white pumpkin may be the one that keeps its composure in the oven.

Perhaps these rheological differences help explain why some pumpkin varieties produce a denser, creamier texture after cooking, while others are better suited for carving than baking.

The answer is both yes and no.

The white pumpkin’s skin consistently showed a slightly higher modulus in both shear and bending, suggesting a somewhat stiffer outer structure. However, the differences were relatively small, meaning most pumpkin carvers would probably be happy with either variety.

The flesh revealed the more interesting distinction. The orange pumpkin appeared more moisture-rich, briefly stiffening as water was lost before softening dramatically at higher temperatures. The white pumpkin responded much more steadily, maintaining its structure over a wider temperature range.

In the end, these pumpkins simply told different rheological stories.

And that’s the fun part of rheology: even an ordinary pumpkin can reveal a surprising amount of science.

So, the next time you’re carving a jack-o’-lantern, roasting pumpkin for dinner, or wandering through a pumpkin patch in search of the perfect specimen, remember:

Behind every pumpkin is a little bit of rheology.

And sometimes the scariest thing about Halloween is discovering that your pumpkin has a higher modulus than expected.