A general rule with regard to brittleness is that a brittle product breaks at very little deformation.  Brittleness is typically a packaging and shipping concern.  Users concerned with brittleness typically measure the distance at which a product breaks.  The firmness at which a product breaks is important with regard to differentiating between products which break at similar distances.

Crispiness is typically a high profile textural parameter for snack foods, baked products, and other foods, such as french fries.  A general rule is that a crispy product's initial resistance to the probe (or teeth) builds faster than non-crispy products.  The initial slope of a texture plot is thus a good measure of crispiness.

Practical solutions, however, are not that simple.  For example, should a manufacturer with a product breakage problem make the product softer or harder?  Common practice might be to make the product harder to withstand greater forces, but a softer product might be more pliable, and thus less susceptible to breakage caused by shocks during production runs.

In the following sets of graphs, choose which is the most brittle and which is the most crisp.  Think about whether these graphs illustrate attributes which your own products exhibit.  Complicating the graphs are instances where the products exhibit early fractures, in thick the products are hard but not brittle.

Graph Set 1 This set is relatively easy since they all break around 700 grams, and yet they do so at very different distances.  Graph A is clearly more brittle than B which is more brittle than C, which is more brittle than D.  Their crispiness rankings are identical since the slope for Graph A is greater than for Graph B, which is greater than Graph C, which is greater than Graph D.

Graph Set 2 This set is also simple since the graphs all break at a similar deformation. It is clear that Graph A is clearly more crisp than B which is more crisp than C, which is more crisp than D.  Graph G breaks at a lesser force, than F, E, and DD, so Graph G would likely be judged by sensory panels as the most brittle.  Graph DD would be the least brittle.

Graph Set 3  This set shows how brittleness and crispiness rankings are more difficult to ascertain.  Graph K is the most brittle since it breaks at the least deformation.  Graph H clearly deflects much more before it breaks and would be the least brittle.  If you measure crispiness as either (i) the initial rate/slope, or (ii) the slope until the break/fracture, then all of the products are identical with regard to their crispness.  As a practical matter a sensory panel would likely judge that H would be more crisp than the others since, the slopes being equal, it is much harder.

Graph Set 4  The rankings for this set are identical to Set 3, with the exception that Graph N is more brittle than M and L since it partially fractured at a lesser deformation.  The fact that N was cohesive enough not to completely break and that it eventually broke at the same force as M does not affect the rankings.

Graph Set 5  Graphs R and P are more brittle and more crisp than Q and S since they break at lesser deformations and the graphs are also more crisp since their initial slopes are much higher than those for Q and S.  Graph P is likely to be more crisp than R, and R is more brittle than P.

Graph Set 6  Graph X is the most brittle and the most crisp, and Z is the least brittle and least crisp.  Graph U is the second-most brittle (since it breaks the 2nd lowest deformation distance) and would likely be judged by a sensory panel as the second-most crisp (since other than T and V it has the second highest slope). Graph W is less crisp and brittle than Graph U. Graphs T and V (and to a lesser extent Y) are firm, but the roundness of their curves suggests that they are more pliable than brittle and perhaps more firm than crisp.  A Tootsie Roll for example would exhibit a firm rounded curve like Graph V.  Graph T's high initial resistance is followed by a relatively flat rolling curve suggesting that it might be a product like a thick french fry which offers structural resistance due to a crisp shell or by its geometry.  Once the product compresses its crispness passes and it is relatively pliable before it finally breaks. A well instructed sensory panel might determine that Graph T's initial resistance makes it the second-most crisp, but that same panel might understand that the product's eventual pliability detracts from its high crispness.