fective toolbox that can overcome each challenge, enabling production people to smile along with their product’s consumers. THE BEAUTY OF COATINGS Ice cream coatings are typically thin layers manufactured from inexpensive fats such as coconut oil or hydrogenated palm kernel. Total fat content is often above 60% so as to achieve a sufficiently thin layer and short crystallization time. From stick ice creams to Eskimo bars, there are many products that can benefit from coating. A typical confectionery coating protects the filling, keeping it inside the praline and ensuring it won’t dry out. Those enjoying the product can hold it with a minimum of mess, and when eaten, a good coating gives a pleasurable and varied experience, both in terms of mouth-feel and flavour release. Much of the credit for this must be given to the special properties of confectionery fats such as cocoa butter, which is uniquely hard and brittle below 30 oC (86 oF), yet which melts in the mouth at 35 oC (95 oF). But there are more challenges, and the list centres around the interaction between filling and coating, with problems showing up, for the most part, not during production but in the days and months that follow: • The coating speed required is far faster than that of other, non-ice cream applications. Moisture will always migrate from the ice cream into the chocolate. Cracking may result if the chocolate is, for example, not sufficiently plastic. Fat can migrate from the filling to the chocolate coating, causing a greyish layer known as ‘bloom’. Alcohol content in the filling may cause instability or even leaking. Yield value (YV) defines the force needed to initiate a flow in a non-Newtonian fluid such as chocolate. The YV is typically important when working at low shear such as when moulding/ vibrating. Plastic Viscosity (PV) defines the force needed to maintain a constant flow in a chocolate. The PV is important when working at medium to high shear such as in the enrobing process. • • • rheology, the crystallization speed of the fat used, and the temperatures of the ice cream chocolate dictate this crucial parameter. To the uninitiated, it may seem that by gaining control of the rheology and ensuring the optimal temperatures of both chocolate and ice cream, all their production problems could be solved. Unfortunately, it’s not that simple. During a production run, the ice cream coating will change its rheology – and that changes the whole game. Imagine for a moment, that you expose an almost water-free chocolate (good chocolate makers do their best to squeeze more than 99% of the water out of their product) heated to 35 oC (95 oF) to an ice cream that is mostly comprised of water – and resting comfortably at around -15 oC (5 oF). What happens? Melted ice cream mix will migrate to the hot chocolate, gradually increasing the latter’s viscosity and Yield Value (YV). And if you’ve set your process parameters less than optimally – perhaps with overly warm chocolate or ice cream whose temperature has climbed just prior to dipping – this damaging effect happens much faster. Why should you care about the YV of the coating starting to increase? Because you’re likely to end up with a gradually thicker layer, the risk of ‘pinholes’ forming when melted and expanding ice cream • I’ll focus on the first three, most important issues for this article. READY, SET, DIP! THE DARK SIDE What makes working with coatings so difficult? For one thing, ice cream is best produced when it’s cold, while chocolate is easiest to work with when it’s warm. For another, chocolate has almost no water content while ice cream is mostly water. So bringing the two of them together is hardly a match made in heaven. In contrast to a traditional coating process, during which crystallization can build up over several minutes, the dipping/coating process required to marry flowing chocolate or chocolate compounds with cold ice cream needs to take place in a matter of seconds. The chocolate moves from a liquid to a solid state extremely rapidly, with no time for regulating the thickness of the resulting layer by blowing or vibration. Instead, the chocolate’s WATER MIGRATION As the YV of the coating starts to increase you may risk ending up with ‘pinholes’ or in extreme cases separation of the coating on the ice cream. 2
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