Stirring honey – an extended view
Author und Editor: Dr. Andreas Kokott (About the Author)
After the honey harvest, the beekeeper has to take care of the honey. The source of the nectar varies depending on the harvest time and the honey solidifies more or less quickly. This is due to the proportions of the various sugars (e.g. glucose or fructose content) in the honey, which vary depending on the time of harvest. Different sugar contents result in different crystal sizes and different crystallization speeds. A high content of triple sugars, e.g. in melicose honey, ensures that the honey crystallizes in the combs and can no longer be extracted.
If the crystals exceed a certain size, they can be felt on the tongue like grains of sand. Unfortunately, customers consider the crystal formation, which is sometimes accompanied by discoloration, to be a defect.
After the honey harvest, the beekeeper has to take care of the honey. The source of the nectar varies depending on the harvest time and the honey solidifies more or less quickly. This is due to the proportions of the various sugars (e.g. glucose or fructose content) in the honey, which vary depending on the time of harvest. Different sugar contents result in different crystal sizes and different crystallization speeds. A high content of triple sugars, e.g. in melicose honey, ensures that the honey crystallizes in the combs and can no longer be extracted.
If the crystals exceed a certain size, they can be felt on the tongue like grains of sand. Unfortunately, customers consider the crystal formation, which is sometimes accompanied by discoloration, to be a defect.
There are various ways to prevent the honey from crystallizing before bottling or at the customer’s premises:
A) The onset of crystallization, which is noticeable through cloudiness, is adjusted and the honey is then stirred for several days in succession. This produces a creamy honey without the annoying large crystals. To ensure that you don’t miss the time of clouding, you can also fill a jar of honey from the storage container and observe it. This means that the storage jar does not need to be opened regularly.
B) Crystallization is induced by inoculating the honey with another honey that already contains crystal nuclei. This starts the crystallization process.
There is already a lot of information on the subject of stirring on the Internet, in specialist journals or books. But what happens during stirring and where do mistakes lurk?
The stirring process
Stirring is the process of distributing “substances” in a liquid. Such “substances” can be liquids (e.g. juice and water), solids (sugar in coffee) or even gases. Mixing takes place due to the flow forces. These depend on the shape of the stirrer, the viscosity of the liquid, the stirring speed, the flow rate (how much is moved per unit of time) and also the ratio of the size of the stirrer to the container or the distance from the stirrer to the base or outer wall.
As agitation is frequently used in industry, it has been extensively studied. The industry wants stirring times to be as short as possible. As stirring represents an input of energy, the temperature can increase during the stirring process and sensitive products can be altered or destroyed in the process.
The aim of stirring is to achieve the same distribution of components at every point in the container. There are extensive studies and corresponding tables that deal with the relevant parameters. In such studies, the stirrers are permanently installed in the container. Therefore, the data cannot be transferred to manually stirred systems. Another complicating factor is that the counting liquid (the parameter is viscosity, measured in millipascals/second, or mPa/s for short) changes considerably with temperature. For viscous products such as honey, the counting liquid (viscosity) at 20 °C (room temperature) can be five times higher than for honey from the heating cabinet at approx. 36 °C.
Crystallization:
We know a simple experiment on crystallization from our school days. Salt is dissolved in water until a sediment forms. The saturated solution is then filtered off and left to stand without being shaken. Over time, salt crystals form.
It’s the same with honey. We have a highly concentrated solution of various sugars in water. The less water content, the more the honey tends to crystallize.
There are two different processes involved in crystallization: nucleation and nucleation growth.
Nucleation:
So-called crystallization nuclei are required to start crystallization when the concentration of sugar is sufficiently high. These can be exogenous and/or endogenous nuclei.
Exogenous nuclei include everything that is not present in the solution, i.e. comes from outside. Crystallization nuclei can form on scratches in the vessel wall, on impurities (dust) or on foreign surfaces (air bubbles).
Endogenous nucleation occurs when the ingredients trigger nucleation. This can happen, for example, when sugar molecules collide or attach to each other.
The first step, nucleation, is very complex. Tiny nuclei are formed. Some of these also dissolve again. Only when the germ reaches a certain size does it begin to grow.
This balance between germ formation and germ dissolution depends on the temperature. The higher the temperature, the more the crystal nuclei dissolve again. This means that you can dissolve more sugar or salt in a warm liquid (e.g. coffee, soup) than in a cold liquid. Theoretically, at low temperatures (e.g. between 0-5 degrees), most of the crystal nuclei would then form in honey, as they are more difficult to dissolve again. However, the viscosity increases dramatically as the temperature drops.
This means that at lower temperatures, it is much more difficult for the particles that assemble to form a germ or that cause germ growth to move through the liquid. This inhibits the growth of the germs.
Nucleus growth:
From a crystal size of around 30 μm (0.03 millimeters), you can feel the crystals between your fingers or on your tongue. In principle, the crystals in honey are a sign of quality. Unfortunately, only a few customers like the “tangible” crystals on the tongue. A special effect occurs during germ growth. Smaller crystals dissolve into smaller crystals so that the larger crystals can grow. This effect is known as Ostwald ripening.
We can now make various statements:
A) Honey storage in the refrigerator or freezer: Stronger tendency to form crystallization nuclei due to the low temperature. However, crystal growth is inhibited because the sugar molecules cannot move towards each other easily due to the higher viscosity.
B) Honey storage at room temperature: Crystallization nuclei form and the crystals grow, as the sugar molecules can move better than at lower temperatures.
C) Honey storage in a heating cabinet: Lower viscosity. Formed crystallization nuclei dissolve again. Larger crystals can dissolve, larger crystals usually remain.
Seeding:
The addition of seed crystals starts the crystallization process. This process is also used in industry. For example, inoculation solutions are used to precipitate crystallized sugar from thickened sugar beet juice. Fine crystals are formed without inoculation. Some of these dissolve again, allowing another part to grow (Ostwald ripening). This results in unevenly sized crystals. Inoculated honey is added to honey. The following factors are important:
The crystal size in the inoculated honey: If the crystals in the inoculated honey are too large, they will grow. You get few, but large crystals. You should therefore inoculate with a very fine crystalline honey. This is either liquid for a very long time (has many nuclei) or is very fine-creamy (has many small crystals). If the number of crystallization nuclei or small crystals is very low, they can only grow a little before growth stops.
The amount of inoculated honey:
If too little inoculated honey is added, there are not enough germs in the honey for rapid growth. You get fewer crystals, but they are larger. Between 5 – 10 % inoculated honey is added, whereby more should be added rather than less.
The inoculated honey must be thoroughly stirred so that it can start crystallizing everywhere in the honey. Inoculating with finely crystalline honey ensures faster and more even crystallization. The germs do not have to form first. You simply add them. This produces a creamy and therefore viscous honey. The viscosity inhibits the growth of crystals.
After inoculation and thorough stirring, the honey should quickly become finely crystalline. As the mobility of the sugar molecules and thus the crystal growth depend on the temperature, the honey should be stored at room temperature of approx. 18-20 degrees, i.e. not too cool.
Stirring honey
Stirring is an important step in the processing of honey. We stir the honey in two cases:
A) At the onset of cloudiness, so that we obtain very fine crystals throughout the honey as a result of homogenization.
B) When inoculated honey is added in order to distribute the crystallization nuclei very finely.
When it comes to stirring, there is a wide variety of “wisdom” based on experience. Unfortunately, false information also persists.
Examples
The crystals are crushed with the right stirrer. Slow stirring is better than fast stirring – or vice versa.
Anyone who has taken an interest in making chocolate knows that granulated sugar is added to the chocolate mixture. The sugar crystals have to be broken up so that you can feel the chocolate “melting gently” in your mouth. The smaller the sugar crystals, the more pleasant the “melting” of the chocolate in the mouth feels. To break up the crystals, the chocolate mass is allowed to run for “many hours” between large rollers that are only a gap wide apart. The crystals are crushed in this narrow gap. The finer the crystals, the more complex the process. Chocolate is like honey. You have to crush the crystals to less than 0.03 millimetres so that you don’t feel a grainy taste in your mouth.
A few minutes of honey stirring (regardless of the stirrer and stirring speed) is no substitute for hours of grinding in a fine roller mill, as is the case with chocolate production). Alternatively, there are also colloid mills, but only for small quantities. These are therefore used in the laboratory.
In such mills, rotors are turned at extremely high speeds at small distances from a shell surface so that the crystals are crushed in a very small gap between the agitator shell and the rotator. As these examples show, it is not possible to simply crush crystals in liquids and it is certainly not possible with a honey stirrer.
Honey stirring only leads to an even distribution throughout the honey. This is achieved by currents. Now there are different types of stirrers. These differ in the flow. It should also be noted that, depending on the type of stirrer, the circulation of the entire contents takes different lengths of time.
If you only stir in the middle and do not bring the honey at the edge and bottom into the flow, large crystals can form at these points. The flow speed at the walls is extremely slow compared to the center of the container. More precisely, there is a layer of honey on the walls and bottom of the jar that is difficult to remove and mix with the honey mass inside the jar. Everyone is familiar with this effect. You can fill the honey well, but a layer stubbornly sticks to the wall of the jar, which you then remove with a scraper.
We have selected two of the many different stirrers as examples:
With a spiral stirrer (helix stirrer), you do not get the edge area circulated if you only hold it in the middle of the vessel. The generated flow is too low. However, you can operate this stirrer at high speeds and move it along the edge without damaging the container.
With a paddle stirrer, it is better to keep a greater distance from the edge of the vessel, as the stirrer can otherwise damage (scratch) the walls. In the worst-case scenario, particles, e.g. from plastic buckets, end up in the honey. Good mixing takes place even at low speeds. If the paddle stirrer is only used in the middle, the mixing depends on the diameter of the stirrer and the diameter of the container.
Axial flow (upper picture)
Radial/tangential flow
Figure 1: Different flow types depending on the agitator type
While paddle stirrers (propeller stirrers) transport the honey from top to bottom or from bottom to top depending on the direction of rotation (axial flow), plate stirrers or grid stirrers push the honey from the center to the outer wall (radial or tangential flow). You can imagine how different the flows and transported quantities are due to the choice of stirrer (Fig. 1)
As shown in Figure 1, you can see that axial stirrers (right) mix the bottom area of the jar better and radial/tangential flows (left) better incorporate the honey layer on the jar wall into the flow.
Due to the various factors involved in stirring (stirrer type, stirring speed, distance to the wall or base, stirring time), different and often contradictory experiences arise. It is therefore impossible to say which is the better stirrer. Even a hand tamper, which mixes the honey by moving it up and down, can successfully produce creamy honey. The most important thing you can say about stirring is to stir thoroughly.
Honey and marketing
Customers are familiar with liquid or creamed honey. It would make sense to use a jar of crystallized honey to show customers that the formation of crystals and the associated discoloration is a normal process that takes place during the storage of honey and is not a sign of inferior quality. With crops and fruit from organic or farm stores, customers also accept that not all cucumbers, potatoes and apples are the same size, the same shape and have a perfect surface. Why shouldn’t honey be the same? An informative discussion provides customers with knowledge, increases acceptance of the natural product and thus also increases customer loyalty.