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Pizza, fondue or raclette would be unthinkable without gooey melted cheese, yet cheeses that don't melt or stretch well could ruin these dishes. Softening point is a key parameter to measure cheese melting properties and ensure a delicious outcome.
Softening point, or SP, is the temperature at which a substance softens and stretches under a defined weight and flows vertically down a defined distance (the flow distance). A ball is normally used as a weight to promote the flow of the substance; using this technique, both thermal values and rheological properties such as meltability, flow propensity and stretchiness (summarized in Table 1) can be studied [1].
Cheese is an increasingly common ingredient in prepared foods. As it becomes elastic at elevated temperatures, SP measurement is an effective means of characterizing its behavior, and food scientists increasingly employ SP to ensure flavorful results.
| Descriptor terms | Definition | Measurement |
|---|---|---|
| Meltability/melt | Tendency to soften upon heating | Softening Point |
| Viscosity/flow | Tendency to spread and flow when melted | Softening diagram |
| Stretchiness | Tendency to form strings when extended | Video |
Table 1: Textural properties of melted cheese.
Procedure
Here, we investigated three melted cheeses using METTLER TOLEDO's Excellence Dropping Point System. Cheddar, emmentaler and mozzarella were subjected to simultaneous duplicate experiments, with each sample measured three times (n=6). The Excellence instrument permits video observation during and after the measurement, as shown in Figure 1.
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Figure 1: View of a typical measurement: in this case, mozzarella samples at the softening point. The horizontal line indicates 19 mm distance. |
During the course of an SP experiment, the flow distance is monitored constantly. SP temperature can be determined at the moment when the sample has flowed a distance of 19 mm; an example of a distance diagram is sketched in Figure 2.
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Figure 2: Temperature diagram of flow distance for a single sample of each melted cheese. |
Because factors such as motion affect the flow of the sample from the cup, the overall force experienced by the flowing sample can be mathematically formulated as follows:
d = c0 + c1*T + c2*[exp(c3*T+ c4)]
(eq. 1)
where:
d is the vertical flow distance
T is the temperature
c0 and c1 are linear terms
c2, c3 and c4 are parameters of the exponential term
The most important parameter is c3, because it indicates how rapidly the exponential function decays – or in experimental terms, how quickly the cheese softens.
In the conventional signal processing field, c3 is known as the time constant (τ) and can be expressed as a reciprocal. Since we are considering temperature and not time dependence, we call this term the temperature constant τT. τT can be obtained after curve fitting and can be used to distinguish between SP samples.
Results
Table 2 summarizes the results of the three melted cheeses. They indicate that, for both SP and τT, there is a progression of results with increasing temperature, and τT from cheddar to emmentaler to mozzarella.
Mozzarella exhibits the highest SP of 72.5 °C – a full 10 °C higher than the other two. The SPs of cheddar and emmentaler are close: 60.1 °C and 62.7 °C, respectively. Should two different cheeses share a similar SP, τT values assist in distinguishing between them.
| Property | Cheddar | Emmental | Mozzarella |
|---|---|---|---|
| SP | 60.8 ± 1.0 | 62.7 ± 1.2 | 72.5 ± 1.6 |
| τT | 0.77 ± 0.18 | 1.48 ± 0.21 | 2.09 ± 0.13 |
Table 2: Softening point and temperature constant (τT) results. Uncertainties express standard deviations (n=6). SP results in °C.
Conclusions
Heating modifies the original microstructure of a cheese, and with it, its texture. SP data indicates the temperature at which this thermal change takes place, while τT indicates how quickly it occurs. Measuring the SP sheds light on the interplay among parameters such as meltability, viscosity and stretchiness in a phenomenological way, providing insight into a cheese's suitability for specific recipes.
[1] R.Kapoor, L.E. Metzger, CRFSFS (7), 2008:194-214.
