Learn the science behind:
A common snack for breakfast, or in between meals, in the Netherlands is a product called ‘ontbijtkoek’, ‘kruidkoek’ or ‘peperkoek’*. It’s best translated as a soft gingerbread cake. It’s soft, and moist, and contains a mix of spices. It’s so common here that I never realized an important curiosity: you can store this ‘cake’ at room temperatures for several weeks, without it spoiling!
Try to store an apple cake, or a pound cake, on the counter for a couple of days, and you’ll be left with a cake full of hairy molds. This is not the case for this gingerbread style cake. It’s soft and moist, but still stays good for long.
It’s a great example of the power of sugar as a preservative at work, so about time we dig into the science of this ontbijtkoek!
*Literal translations of these Dutch terms into English would be: ontbijtkoek = breakfast cookie ; kruidkoek = spiced cookie ; peperkoek = pepper cookie.
Ontbijtkoek, or kruidkoek, has been around for centuries. Armies used to take products like it with them since they could be kept for long periods of time and contain a lot of energy. Initially these cakes would be made with honey. However, with the increased supply of sugar and sugar syrups, honey was replaced by cane and beet sugars over time.
An important component of these cakes have always been their spice mixes. Spices were very expensive in western Europe in the middle Ages and as such, ontbijtkoek was a true luxury product. At times, the blend of spices was regulated in parts of the Netherlands, to prevent manufacturers from misleading their customers. With spices becoming cheaper and more widely available, products such as ontbijtkoek grew in use among poorer parts of the population in western Europe.
Different regions in the Netherlands each developed their own preferred types of ontbijtkoek. Some are more heavy on the aniseed, others are more strongly spiced overall.
Ingredients of ontbijtkoek
Ontbijtkoek is made of just a few ingredients: sugars (incl. sugar syrups), rye flour, some water, salt, baking powder and a spice blend. The baking powder is added to improve the airiness of the ontbijtkoek and the salt adds a little flavor. The spices give the ontbijtkoek its characteristic deep flavor profile. They are quite common in cakes, instead, we’ll focus the rest of our attention on the sugars, rye flour, and the absence of fat.
To start with the last ingredient in our list: fats. Notice in the recipe below that ontbijtkoek does not contain any added fats in the form of oils or butter/margarine. Whereas a cake would turn dry without any fats, that’s not the case for ontbijtkoek. The high amount of sugars helps keep the ontbijtkoek nice and moist.
One of the core ingredients of a good ontbijtkoek, Dutch gingerbread cake, is rye flour. Rye flour tastes and behaves different from ‘regular’ wheat flour. First of all, rye flour does not contain gluten proteins. When making bread this is a disadvantage since gluten help create a network within a bread dough that can hold on to air. However, when making ontbijtkoek we don’t need this network. Not having the gluten is even a slight advantage since you won’t overmix the dough as easily.
Secondly, rye flour can hold onto water a lot better than wheat flour can. Rye flour contains large molecules (polysaccharides, specifically pentosans) that can absorb and hold on to a lot of water. It is also why products made with rye flour need more water and also become sticky and tricky to handle (as is also the case for ontbijtkoek).
These pentosans are what give ontbijtkoek its characteristic texture and they also help keep the ontbijtkoek fresh for longer! Breads and cake turn old and stale because of the retrogradation of starch. Pentosans slow this process down.
The main structure of the ontbijtkoek is formed by rye flour and sugar syrups. More specifically, sugar syrups made from cane or beet sugar such as “candy syrup”. These syrups are brown, thick and viscous. They contain a mix of sugar molecules (not just sucrose, your ‘regular’ sugar) as well as some molasses.
The water from the sugar syrups is bound by the rye flour, helping creating that soft texture. The sugars themselves are dispersed all throughout the product. They make the product sweet, but also provide a hint of bitterness and sourness.
Why does ontbijtkoek keep so well?
That brings us to our earlier observation: ontbijtkoek can be stored at room temperature for weeks without spoiling. It might turn a little drier over time, but it won’t actually spoil easily.
In order to understand why that is the case we have to look at when and how microorganisms grow. Microorganisms are tiny (micro) organisms that live all around us. Bacteria, yeasts and molds are all common examples of types of microorganisms that can occur on our food.
Most microorganisms are quite sensitive to heat so when you’re baking ontbijtkoek, a lot of the microorganisms in and on the cake will be killed. Once the cake is out of the oven though, microorganisms from the air will again sit on the cake.
For microorganisms to grow on the cake (and spoil it) they need to have access to sufficient food (nutrients, e.g. sugars) and water. Also, the temperature should and the pH-value (measure for acidity) shouldn’t be too low.
Water activity of ontbijtkoek
In the case of our ontbijtkoek, there are plenty of sugars for the microorganisms to grow and enjoy. Also, with it being stored at room temperature, the temperature is great for growth of a lot of microorganisms that could spoil the cake.
However, where it gets tricky for the microorganisms is the available water. The amount of available water in our food is given in a value for the water activity. A value of 1 means all water is ‘available’, a value of 0 means there is no available water at all. Most microorganisms need a water activity value >0,8. Only a select few can grow at values lower than that.
A common way to lower the water activity is by adding sugar to a product. The sugar binds the water and as a result, it can’t be used anymore by the microorganisms. This is what happens when making ontbijtkoek, a lot of the moisture is bound by sugar! As a result, a common water activity for ontbijtkoek is 0,8, sometimes lower, which prevents growth of a lot of microorganisms!
pH-value of ontbijtkoek
Preserving food always goes best when several measures are taken simultaneously. This is often referred to as the hurdle approach.
In the case of ontbijtkoek the other hurdle that’s been put in place is the pH-value. Sugar syrups as well as honey tend to be on the acidic side of the spectrum. It is common for them to not be higher than 5. As a result, the ontbijtkoek is slightly sour. Combine this with the lower value for water activity and growth of microorganisms is slowed down quite a bit.
One more hurdle: spices
The last hurdle that can be thrown up against microorganisms in ontbijtkoek is the presence of spices. It has been shown that various spices, e.g. cinnamon, delay growth of microorganisms. Since this cake contains a good amount of spices, it is likely that they also help in keeping the ontbijtkoek good for long!
J. Kramer, Lebensmittelmikrobiologie, Ulmer, 5. Auflage
Nathan Myrvold, Francisco Migoya, Modernist Bread, 2 – Ingredients, 2017, p. 2-254 – 2-257
NBC, Bederfelijke producten, link
Clemson, pH Values of Common Foods and Ingredients, link