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Dunk and Disorderly

Dunk and Disorderly

By Richard Temple and Jamie Dodger
Centre for Imbibing and Infusion Studies, University of Bristol, UK.


What could be better than a piping hot cup of tea and a nice biscuit? Very little, we think. The cuppa, and the baked goods we dip into it, are cornerstones of our society (Bonds 1989), without which many of the world’s finest ideas would never have been thought up or discussed. However, when the biscuit selection comes round, there is a potential minefield of problems and dunking the wrong biscuit for the incorrect amount of time can lead to a crumbly catastrophe. Here we present a study on seven well-known and popular teatime accompaniments, to find just how long they should be dunked, to avoid a contaminated cuppa.


Each biscuit was first tested for crumbleability by using the crumb index - Ci (Godard 1982). In this context, it is the force needed to reduce a biscuit structure from ‘whole’ to ‘bits’. Correction factors were required for biscuits containing chocolate (Cocoa correction - CoCo) and those containing grape-derived dried-fruit products (GDDF factor). Powdered cocoa used in the core of some biscuits such as Bourbons and Maryland cookies (double chocolate forms) did not need correction, as their cohesive properties were not affected. Bourbons and custard creams do, however, have a filling factor (ff) due to the creamy centre, as this can increase the bonding between layers. Such filling corrections are well understood (e.g. see Brody & Cochran 1976) and are adjusted for in this study.

A lot of tea (Camellia sinensis L.) was prepared. Experimental tea was always at the maximum infusion temperature (boiling +/- 10oC). Milk was added after the infusion and the biscuits were then tested.

Each biscuit was dunked for one second and then withdrawn for one second (Figure 1), with this pattern continued until the biscuit's internal structure became saturated, and subsequently failed. This is known as the ‘plop point’ (Pp) and is accompanied by the all-too-familiar disappearance of the wet half of the biscuit into the cup, with ensuing cursing and teaspoon dredging.

Time to internal failure (to reach Pp) was recorded for each biscuit and repeated for the entire packet. All dunk-times were recorded using an atomic clock. In  tact biscuit halves were kept for later snacking.


The HobNobs™ seemed to be least tea-friendly (Table 1), while Garibaldi biscuits were the most stable, although after correction for GDDFf they lost some of their appeal. The ginger nuts had the highest crumb index and required a lot of force to break up into pieces. Their subsequently high plop point was not surprising, really taking the biscuit. Bourbon and custard creams had similar properties and behaved alike in all tests. Digestives were dull, in colour, shape, texture, behaviour, etc...


Garibaldi’s and ginger nuts are tough cookies… Digestives and HobNobs™ are not, the latter seeming to be the most crumbly; the large number of oats causing unrest within the mix, leading to an oat-so unstable biscuit, a quantity problem that has been repeatedly questioned (Pendlebury 1982).

The cream filled biscuits (Bourbon and custard creams) and the Maryland cookies (with their cunning chocolate additions), behaved similarly. The creamy interior added cohesion to the biscuit exterior, like a rose between two thorns. Independent testers concurred that either a tasty interior stratum or chocolaty add-ins significantly improved the taste, but not the plop point time. Garibaldi’s, with their unique form and surface glaze lend themselves to the more astute tea drinker. Conversely, ginger nuts, with their unyielding temperament and constitution make fine dunkers, consistently performing to the highest level whilst always satisfying the dunkerer.

Figure 2 clearly shows that digestives cannot be trusted with hot beverages.

Although each biscuit behaved differently in tests, all possessed a liquefaction zone (Figure 3), a property that defines the Pp, and is the area of the biscuit that becomes tea-saturated. Moisture builds up in the centre zone, which becomes unstable, loses strength and acts as a liquid. A similar effect has been found during earthquakes (Ishihara 1993).

Why are digestives so popular?

Biscuits will always play a pivotal role in our elevenses. Throughout time they have been the cause of common-room conflicts, party politics, governmental wrangling and international deliberations. The Bourbon and the Garibaldi have been at the heart of this, causing disturbances wherever they are dunked, most notably in Italy where anti-biscuit feelings ran high in the 19th century (Calleri 1998, answered in Pacifici 1998), and in South America, where Garibaldi’s were, at one point, the biscuit of choice (McLean 1998).


We suggest you stick to a few favourite biscuits and remember their Pp times… that way you’ll never be caught short at an important meeting. Avoid oat-based cooked biscuits that fracture easily, leaving basal cup-sludge. Steer clear of digestives; they are only good for cheesecake bases. Eat more Maryland cookies.


Bonds, D. (1989). The ‘cup of tea’. Southern Humanities Review 23, 342.

Brody, H. and Cochran, W.M. (1976). Shortenings for bakery type cream icings and fillings. Journal of the American Oil Chemists Society 53. A460.

Calleri, S. (1998). The anti-Bourbon uprisings in Messina in 1847 and 1848 (comments on an article by Vincenzo Modica). Historica 51, 134-137.

Godard. H.P. (1982). The crumb index: A challenge. Materials Performance 21, 7.

Ishihara, K. (1993). Liquefaction and flow failure during earthquakes. Geotechnique 43, 351-415.

McLean, D. (1998). Garibaldi in Uruguay: A reputation reconsidered. English Historical Review 113, 351-366.

Pacifici, V.G. (1998). Pro-Bourbon reaction in Calabria-Ulteriore-2 (1860-1865) by Gallo RF. Rassegna Storica del Risorgimento 85, 77.

Pendlebury, M. (1982). Hob, nob, and hecate: The problem of quantifying out. Australasian Journal of Philosophy 60, 346-354.

Perry, J.A., Swanson, R.B., Lyon, B.G. and Savage, E.M. (2003). Instrumental and sensory assessment of oatmeal and chocolate chip cookies modified with sugar and fat replacers. Cereal Chemistry 80, 45-51.

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08 May 2011
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