Today’s test subject is the Dutch pepernoot, a typical holiday-time cookie enjoyed mainly around the Saint Nicolas (or Sinterklaas) celebrations in early December. They’re made from different spices, like cinnamon, nutmeg, cloves and ginger.

To see what makes a pepernoot good, Bruker, an American companyknown for high-resolution 3D X-ray imaging, ran the cookie through X-ray microscopy (XRM). The point isn’t to ruin the Christmas magic, but to quantify it: the measurements are used to sharpen the recipe and keep quality consistent from batch one to batch one hundred.

Here’s how it works. The X-ray first produces 2D radiographs of the cookie. Lighter parts of the radiograph show elements like contaminants, and the darker parts are the air bubbles. The dense parts show up lighter, the less dense parts darker. Imagine a process similar to medical CT scans, just used in food science instead of bodies.

A software then combines these 2D scans from multiple angles until it magically becomes a 3D model.

We can then map different properties of our cookie: the gaps between grains, the thickness of the crust versus inside, the consistency of the coating, and even the size and distribution of air bubbles.

“For cookies, crunchiness is an important parameter,” Petra Först, an associate professor of food process engineering at the Technical University of Munich, told The European Correspondent.

Crunch, she explains, depends on the 3D structure – the air bubbles and the skeleton of baked dough, as well as how hard that skeleton is.

Structure also affects how we perceive flavour: liquid and warm forms of food tend to taste stronger than solid and cold forms. Creaminess can enhance sweetness; crunch can make the flavour more intense. When combined, you get a perfect chocolate-covered pepernoot cookie.

The big advantage of XRM, Först adds, is that it delivers the 3D information without destroying the sample, unlike many other microscopic techniques.

Photo credit: Bruker.com

What you’re seeing here is the impact ofbaking. Smaller air bubbles sit closer to the pepernoot’s chocolate coating, whereas bigger bubbles gather closer to the centre. The colours indicate the size of air bubbles. No cracks and no larger air bubbles usually mean that the bake went right.

And what about the baking process itself? Cookies are only a start. A 2023 studycompared different bread-making methods (microwave, a traditional oven, and combined heating), focusing on pore size distribution rather than crunch.

“This is especially important when developing new recipes, like cookies or bread for people with gluten intolerance, where wheat has to be replaced by other cereals,” Först explained.

In practice, this means we can make better recipes for gluten-free breads, maybe even some that don’t feel like you’re eating cardboard. XRM can also indicate which part of the baking process needs improvement, whether the goal is better crumb, more energy-efficient baking, or a longer shelf life of the end product.

The future of food design

XRM goes well beyond examining your holiday cookies. Researchers also use it on fruits, dairy and meat products. A study from the University of Copenhagen, for instance,points to its potential for designing foods that would be broken down by the body to maximise the nutrient intake.

Similar tools are also used tostudy how milk proteins behave in different sustainable processing methods, and how to recreate the same characteristics people love in cow milk in more sustainable alternatives. In theory, scientists can imitate the “original” feeling by using the plant-based ingredients, but in practice, more research is needed.

University labs will continuedeveloping even more sophisticated ways of analysing food, down to cells and molecules.

At the Technical University of Munich, for example, scientists useatomic force microscopy to see how food molecules interact with receptors in our mouths. The focus then shifts from what’s in a cookie to why certain foods taste and feel better when we take a bite.

Imperfect perfection

I will leave it to you to decide whether the special taste of Christmas cookies comes from nostalgia or the geometry of air bubbles. The recipe can be perfected to the maximum, but either way, their roots are very human: sugar, spice and celebration.

In Europe, Christmas baking partially morphed out ofmedieval trade routes. Sugar spread during the 8th century during the Muslim conquest of Spain, and later, spices arrived. But spices were expensive, and people saved these ingredients for special occasions, and wintertime had plenty of those: Christmas and the winter solstice.

And those cookies were easy to make, they would last a long time, and were easy to share among a lot of people. Et voilà, a staple of many Christmas tables was born.