Perforated biscuits

When dunking circular biscuits (and please note that I am using the word "biscuit" in the English way, as a brittle baked item which is usually, though not necessarily, sweet), it often happens that the diameter of the biscuit is greater than that of the mug.

Advanced amateur dunkers, as well as professionals, tend to get around this problem by first breaking the biscuit in half. The ideal - as judged by the Greater London and Regional Biscuit Dunking Advisory Panel - is for the biscuit to break diametrically into two identical halves. Each half can then be dunked to the officially mandated 35% level.

However, snapping brittle items such as biscuits is never straightforward. Homogeneous, fine-grained biscuits such as digestives will generally (though not always) fracture satisfactorily. But coarse-grained biscuits such as the HobNob may have their fracture line diverted - or even branched - by local structural elements at the meso-scale. The result can be an unevenly fractured biscuit, where one part is still too large to dunk, and the other is too small for convenient dunkage. Worse yet, the biscuit may undergo catastrophic failure by breaking into three or more pieces, one of which will inevitably end up either in the beverage (a so-called "floating dunk", which leads to all sorts of problems) or on the floor.

A simple remedy to this serious problem exists. Biscuits which are both circular and large should be baked with a set of perforations across their diameter. To a limited extent, these will act as stress concentrators; but the inhomogeneity of the biscuit means that stress concentration cannot be depended on for reliable crack propagation. It will therefore be necessary to ensure that the perforations are sufficiently close-spaced, relative to their dimensions, to cause appreciable local weakening of the biscuit material. For safety, MaxCo. engineers recommend a perforation spacing of no more than 1.5x the hole diameter.