By Jørgen Holdgaard, Confectionery Application Manager, Confectionery and Bakery Group, Palsgaard A/S. Keeping rheology simple and accessible can cause problems in the daily production of chocolate due to lack of information. Moving beyond single-speed chocolate viscosity measuring to flow-curve or three-step viscosity measuring, allows for a better understanding of practical production situations such as moulding and enrobing as well as the true savings of optimal emulsifier usage. The overall idea of rheological chocolate measurements is to give information of any chocolate or compound’s workability in moulding, enrobing, panning, spinning, shell moulding etc. In order to obtain this, a more informative way of measuring rheology is needed. Historically, the confectionery industry has been working with relatively simple instruments to obtain information of chocolate and compound textures. The Ford-cup beaker, the Mac Michael viscometer and single-speed viscosity measurements are still being used to measure the flow properties of chocolate and compounds. However, the art of measuring chocolate flow properties can and should be evaluated, as the results obtained is only indicative and does not include vital information. In the factory, semi liquid chocolate is a mixture of solid particles - sugar, cocoa and milk - floating in a surrounding continuous liquid fat phase. Because of this, chocolate (and similar confectionery systems) is a non Newtonian substance, see Table 1. Newtonian substances, such as liquids, see Table 2, have constant viscosity (texture); independent of shear rates (speeds), while non Newtonian substances have different viscosities at different shear rates. Table 1: Viscosities of a 30% TF milk chocolate at 40ºC (104ºF) (Non-Newtonian substance). Shear rate Viscosity 100 rpm 6000 Cp 50 rpm 6400 Cp 25 rpm 7000 Cp 10 rpm 8000 CP 5 rpm 12000 Cp 2 rpm 40000 Cp Internationally it has been defined to measure chocolate rheology slightly above the cocoa butter melting point, at 40ºC (104ºF). Table 2: Viscosity of milk at 25ºC (77ºF) (Newtonian substance). Shear rate Viscosity 100 rpm 120 Cp 50 rpm 120 Cp 25 rpm 120 Cp 10 rpm 120 Cp 5 rpm 120 Cp 2 rpm 120 Cp If two different people measure the viscosity of the same chocolate and they uncritically just measure the viscosity at 40ºC (104ºF), they will come up with two different chocolate viscosity values, depending on their chosen shear rates. Milk, or other liquids, would have come back with identical viscosity results. Hence, measuring single shear rate viscosity in chocolate does not provide sufficient information. Single-speed measurements Many producers have used an elderly method when evaluating chocolate flow properties for a long time. This single-speed evaluation method was originally created so that everyone with even a simple viscometer could use it. However, there is a relation between production type and chocolate flow, hence more shear rates are needed to describe the link between chocolate shear rate and the measured viscosity. During chocolate moulding, the chocolate speed is low (0.1-5 [1/S]) while the chocolate moves relative fast at the blowing stage of enrobing (>25 -30[1/S]). Simple instruments and measuring methods all look at limited numbers of shear rates, often only one. Using the single-speed method, it is possible to obtain good pumping information of the chocolate but it doesn’t give any indication of moulding performance, enrobing layer thickness or feet forming. There is no proper viscosity overview when relating measurements to practical production situations such as moulding, shell moulding and enrobing. Moulding evaluation Out of the depositing and vibration aspects of chocolate moulding, vibration has the most crucial impact on the final product. During depositing, the chocolate moves relatively fast, while vibration makes the chocolate move quite slowly and spread out into all impressions of the mould. To properly evaluate a moulding chocolate you need to Palsgaard Technical Paper - January 2012 The importance of expanded rheology information and emulsifier functionality in chocolate production 2
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