Rumoured to have been created centuries ago in Jamaica, chocolate milk may first have seen the light of day as the shavings of freshly harvested cacao, boiled with milk and cinnamon by locals and consumed as a hot beverage. Later, the drink was introduced to England by a Irish botanist where it was primarily used for medicinal purposes.
Of course, cacao has been known in Europe since 1502, when Columbus returned with samples from the Americas. And we can be quite sure that the pioneers of chocolate milk also noted the simple fact that the drink’s particles, if left undisturbed, gradually ‘settle out’ as sedimentation in the bottom of their cups, bowls or whatever else they were using at the time.
Sedimentation was most likely a problem for chocolate milk over 500 years ago, and it’s still a problem now – only these days, the problem has reached an industrial scale, and it applies to many more milk drink and particle types than chocolate alone.
Shake before use
Consumer ideas of what constitutes a desirable chocolate or enriched milk drink can differ widely. For example, some expect it to be highly viscous – others prefer a more plain, milk-like viscosity. Sedimentation, too, while considered by the vast majority of manufacturers to be a problem, may even be treasured by some consumers as a core brand attribute, as is the case, for example, for the traditionally glass-bottled Cocio brand of chocolate milk in Scandinavia.
In that same Scandinavian market, however, and in other markets around the globe, sedimentation is an undeniable problem, particularly in cartoned packaging, as consumers often forget to vigorously shake the carton before consumption, resulting in a drinking experience that varies almost with every sip. Further, labels saying “shake well before use” or the more physically demanding “shake vigorously before use” may be perceived negatively, perhaps because they call attention to the presence of added substances. But such labels are having to be applied to a growing variety of chocolate and enriched drinks, as we shall see.
From chocolate milk to everything-else-milk
Dairy manufacturers have been quick to jump onto the healthy living bandwagon, developing new products with added vitamins, iron, oat fibres, calcium, conjugated linoleic acids (CLA), magnesium and more. The same issue, however, raises its ugly head: adding most things to milk will destabilise the product and endanger both on-the-shelf appeal (for bottled products) and consumer enjoyment (for both bottled and carton products). Even coffee milk, while not widely considered a health-driven product, suffers from the same effect. And a related problem, in long shelf-life products, is the phenomenon known as ‘creaming’.
Sedimentation begins the moment the drink has been produced. But, of course, it really starts to work its dark magic once on the shelf. At worst, two distinct layers can appear. In chocolate milks, the bottom one is an (appropriately) dark chocolate colour, while the one just above it has been described as having a “white-livered” appearance by at least one source*.
In assessing the sedimentation aspect of such drinks, sensory evaluations tend to focus upon:
• The amount of sedimentation
• The fineness of the sediment
• The ease or resistance with which it remixes with the milk when shaken
While some particle-containing drink manufacturers have managed to work out how to achieve a consistent and strong suspension, many others, however, have not. For this latter group, there is much to be gained by deploying up-to-date techniques to combat the problem.
Four networks acting in concert
Essentially, any drink containing insoluble particles is prone to sedimentation. Their resistance to sedimentation, if it is to be effective throughout the shelf-life of the product, first requires manufacturers to consider the choice of milk and particle type.
To reduce the likelihood of sedimentation, state-of-the-art recipes for chocolate drinks based on fresh milk can make the most of four distinct, yet interacting networks that together enable an extremely robust suspension, keeping cocoa particles in their place while ensuring emulsion stability, creaminess and other benefits.
Four of the five networks we’ll discuss in this article are physical effects enabled by:
- Emulsifiers, which increased flocculation of fat globules to form a three-dimensional network
- Stabilisers, forming the essential carrageenan network
- Microcrystalline cellulose (MCC), whose effect on the formation of hydrogen bonds forms yet another network
- In chocolate milks and other enriched milk drinks that may contain cocoa powder, the tannin component in the powder bonds proteins to add further strength to the drink’s suspension
If all four of these networks are present, as they may be in a sophisticated product, the combined result will hold the cocoa particles – or other particles contained in enriched drinks – tightly in suspension, preventing them from migrating to the bottom of the container. It’s a ‘thixotropic’ network, referring to the fact that if shear is introduced to the suspension, for example by stirring, the network will be broken down, but will tend to revert to its pre-shear state again once the disturbance stops.
Of course, gravity means the network is also subject to subsidence under its own weight, but this is countered by adherence to the inside of the container. And at the same time, the stabilised network improves the drink’s mouth-feel.
Network No. 1: Carrageenan
Extracted from seaweed, carrageenan is by far the most commonly used stabiliser in chocolate milk. In Europe, carrageenans are divided into two distinct groups: Refined carrageenan (E-407); and semi-refined carrageenan (E-407a), both of which can be used in chocolate milk. And it’s a sub-group of these, namely Kappa carrageenan, whose chemical composition has proved useful in chocolate milk because of the way it reacts with milk proteins to form a three-dimensional network.
Essentially, the carrageenan forms a helix with negatively charged sulphate groups turning outwards. This helix interacts with the positively charged casein micelle. When carrageenan is used as a stabiliser, and in order for the network to be formed, the chocolate milk must be cooled to below 25°C before filling, or below 25°C during constant rotation if in-can or in-bottle sterilisation is used. It’s important to store the product at temperatures below 30°C, as the network will start to break down in the heat.
Figure 1 shows how this network is formed in a carrageenan-stabilised chocolate milk.
Dosaging carrageenan is somewhat like walking a tightrope. And it’s a fine line indeed: A dosage that’s just a little too low will quickly produce undesirable levels of sedimentation. Slightly overdo the dosage, on the other hand, and the product is likely to acquire a heavy, gelated body.
So the margin between the two states is narrow. Unless, that is, the stabiliser is accompanied by mono- and diglycerides. This increases the dosage margin, and has the useful effect, due to the creation of a network between fat globules and whey proteins, of reducing the amount of carrageenan required to form a stable product. But more on that in a moment.
Another factor to be taken into account, of course, in determining the right dosage of carrageenan, is the variation that may occur in the composition of the milk, depending on the season. But there’s more still to the dosage decision. It also depends, for example, on:
• The milk’s fat content, as more fat requires less stabilising
• The cocoa content, because more cocoa demands less stabiliser
• The choice of heat treatment (Sterilisation requires less stabiliser than UHT, which in turn requires less than a pasteurised product)
Network 2: The MCC/CMC complex
To consumers, it may seem surprising that refined wood pulp has a contribution to make to keeping milk drink particles in their place. But microcrystalline cellulose (MCC), as it is officially known, or rather a MCC/CMC complex, is often used in combination with carrageenan.
MCC is derived from plant fibres from which the crystalline part of the cellulose is extracted. In a dispersion, MCC forms hydrogen bonds, creating the second of our three-dimensional networks. As an added bonus, MCC-based products can also lend more body and creaminess to the drink.
At temperatures below 80°C, MCC’s functional properties are largely unaffected by fluctuations, so cooling and storage temperatures become less critical. That makes MCC-based products a good choice where cooling below 25°C isn’t an option – or if the storage is likely to be at more than 30°C, as is often the case in South East Asia or the Middle East, for example.
Figure 2 illustrates the network formation brought about by MCC/CMC, in which particles are suspended.
Because MCC doesn’t react with the milk proteins in the same way as carrageenan, the risk of separation due to overdosing is less. That said, overdosing will result in heavy body and high viscosity.
Network No. 3: The effect of carefully selected emulsifiers
The emulsifiers used in enriched milk drinks are typically mono- and diglycerides produced by the reaction of edible vegetable fats or oils when combined with glycerol. The resulting molecule (Figure 3) is composed of a hydrophilic and a lipophilic part, positioned at the interface between fat and protein on the one hand, and water on the other. These molecules are formed during homogenisation and ageing of the product.
The mono and diglycerides form a complex with the whey proteins, making the fat globule membrane more resistant to coalescence, and reducing fat separation in the product at the same time. But that’s not all – these emulsifiers lower the net charge of the membrane, creating a three-dimensional network that acts to increase the creaminess of the milk – and the consumer’s sensory perception of a thick, luxurious product. Importantly, and perhaps somewhat counter-intuitively, the emulsifiers also guard against creaming in the finished product.
Network No. 4: Cocoa particles
For chocolate milk drinks, the work performed by carregeenan, the MCC/CMC complex and emulsifiers to create a robust suspension is further assisted by the cocoa particles themselves. A typical recipe contains around 1-2% cocoa powder – meaning there’s no shortage of particles to distribute and hold in position.
From the moment the milk and cocoa powder are mixed, casein is almost immediately adsorbed to the particles. The strength of this particular network-building effect depends on the degree of alkalisation of the cocoa powder. That’s because cocoa powder contains polyhydroxyphenols, which polymerise during alkalisation into tannins, known for their protein-binding properties.
In general, the heat stability of chocolate milk is lower than that of milk, however, the closer the pH of the cocoa powder is to the pH of the milk the less impact it has on the suspension’s stability. It is important, too, to consider the particle size of the cocoa powder, as the network simply can’t support particles that are too heavy. In fact, Palsgaard recommends that less than 0.5% of the particles are larger than 75 micrometers.
Of course, the advantages of this fourth network are lost on enriched milk products that don’t contain cocoa powder. Calcium-fortified, non-chocolate milks, for example, which face the task of suspending particles of calcium instead of cocoa, are similarly subject to unattractive settling, but lack the networking effect of their cocoa cousins. Yet the suspension challenge is no less important to address. For example, where sedimentation has occurred, the consumer may lose the fortifying benefits of the drink – and, at worst, ends up with a mouthful of solids and a distinctly chalky taste.
The creation of a durable suspension in this type of milk drink can largely be achieved, for example, by combining a small-particle-size, solid-precipitated calcium source with the networks built by the combination of carregeenan, the MCC/CMC complex and gellan gum, together with the right choice of emulsifier. Gellan gum is a polysaccharide produced by fermentation that creates a gel structure in solutions, keeping the calcium particles in suspension. The gellan network is formed independently of the proteins in the drink and has only limited influence on viscosity, making it well-suited for a plain milk product.
As with cocoa-based milk products, there is, however, one more network that can make a significant difference, and which can only be created with many years of experience.
The Fifth Network: Global know-how
Working with the four preceding networks isn’t something one can expect to get right first time. In fact, it takes in-depth experience and a lengthy track record of varied recipes and testing before it is possible to quickly determine the right balance of ingredients and effects. So, in fact, there’s a fifth network that plays an important role in achieving the best results: Palsgaard’s own, global knowledge network.
After many years of supplying the dairy industry with emulsifiers and stabilisers, we’ve managed to build up a significant knowledge bank that supports our customers in arriving at the right recipe, equipment and process parameters in far less time than might otherwise be expected. It’s the result of countless trials conducted in well-equipped application labs around the world. In Denmark, Singapore, Mexico and China, for example, application specialists spend days on end to create blends that take key factors such as milk quality, recipe, process conditions and sensory preferences into consideration. The labs are able to perform systematic trials with pasteurised, UHT or sterilised products, making shelf-life studies that cover the entire shelf-life of chocolate or enriched milks.