The Rabbit Whole

This essay was a submission (against the advice of my peers) toward my physics undergrad in 2008. It was written at a time when I was feeling particularly frustrated with the lack of creativity on the course. Accordingly, the recipe was one part a testament to my love of tea, to two parts absolute mockery of the scientific establishment. It was a sort of litmus test of the physics department’s sense of humor, knowing full well that the outcome was going to be one of two extremes. Fortunately, it was well received, commended and posted on the IC website for some years. I’ve always had the sense that my academic tutors finally understood me that day…


Jamie Perrelet
Imperial College London

“Fancy a cuppa?” the infamous calling sound of that notorious British trait whereby one drops everything to indulge in a hearty cup of tea. As a nation we consume more tea per capita than any other country, necking 60.2 billion brews annually, the average Brit will work their way through 74,802 cups of tea in a lifetime. For many of us, tea is an intrinsic quality of our daily being. From serving us at the most desperate of times to being a casual icebreaker at an awkward moment; tea has it all. In the words of four times Prime Minister, William Gladstone:

If you are cold, tea will warm you. If you are too heated, it will cool you. If you are depressed, it will cheer you. If you are excited, it will calm you.” (1865)

Saying this, it is tea’s famed accomplice, the biscuit, under the spotlight today. With a collection of manufacturers in the industry combining to make an assortment of biscuits in the hundreds, there is clearly no shortage of cookie lovers in the UK. Biscuits are not, however, a newfangled creation of recent times, early records show that in Rome there were biscuits as far back as the second century. Also, the word ‘biscuit’ is a derivation of the Latin phrase ‘bis coctum’, which translates ‘twice baked’. Biscuits of the era are described as being unleavened, tough and dry; the lack of moisture extending the shelf-life of the food. This isn’t the most mouth watering description of our beloved biscuit, but there is hope. According to historians the oldest cookie recipe dates back to seventh century Persia (Iran), one of the first countries to cultivate sugar.

Slam Dunk – Quick Start Dunking Guide

That heavenly moment, when biscuit first collides with tea and tea accepts the gathering explicitly, a momentary union, followed by a passionate amalgamation and alike two lovers, the tea and the biscuit have become one.

selection3Step 1: Selecting your biscuit

First of all you need to find your perfect dunking partner; you may require a few moments to think this through. When you are ready, brace your companion firmly using your index and middle fingers on one side and your thumb on the other to form a clamp around the top of the biscuit.

dunk3Step 2: The dunk

Now send your biscuit plummeting into the tanniny depths of your cuppa, a swift motion, with biscuit perpendicular to tea is recommended as this minimises turbulence, thus avoiding structural fractures on entry. Ensure that the biscuit is submerged to its full capacity, leaving only millimetres between your fingertips and the surface of the tea, unless of course you are of the double-dunker variety. Next, the most challenging moment of all, just how long do you drown your sugary treat for?

An impatient or less adventurous dunker will find themselves with a disappointing half-soaked sort of muddle if they don’t honour their biscuit with enough down time, in the trade we call this ‘undercooking’ the biscuit. On the other hand, less careful or over ambitious dunkers may overcook their biscuits and find themselves in a catastrophic situation, whereby the structural integrity of the biscuit fails and debris fall into the tea. Neither of these events is desirable.

eatStep 3: Exit and consumption

If one manages to avoid both rushing and neglecting the biscuit, carefully remove it from the abyss, being cautious of postdunk breakup and contentedly devour, maintaining a broad smile.

In the Laboratory

Of course any investigation requires a laboratory and it was decided that the most apt setting would be the lounge, being the location of peak tea consumption in the house. The apparatus: 1 kettle, 6 cups, 1 full fat milk, 1 skimmed milk, 8 varieties of biscuit, 240 teabags, 1 tap, a little sugar and 5 friends.

Dip, Dip, Dip Test:

In this experiment the dunker is asked to periodically dip a selected biscuit into their tea, the assessor is reminded to count the number of dunks as they go along. The dunking ends the moment the integrity of the biscuit is no longer complete and the number of dips is recorded.

The dip, dip, dip test is designed to identify the ability of the biscuit to survive the harsh and abrupt conditions associated with dunking.

Straw Test:

In this experiment the examiner attempts to use the biscuit as a straw, sucking the tea up through the biscuit until the tea reaches the assessors mouth. The time taken to achieve this is noted.

The straw test is designed to illustrate the porosity and absorption capabilities of the biscuit.

The Contenders

With apparatus in place and dunking fingers at the ready, it’s time to introduce the stars of the show. In the ring today we have ginger nuts, chocolate digestives, custard creams, bourbon creams, jaffa cakes, chocolate chip cookies, jammie dodgers and last but by no means least chocolate hobnobs.

Ginger Nuts:

Her Majesty of the biscuit world, don’t let the ginger nut’s apparently bland appearance fool you. The moment you unlock the flavours from her golden core you’ll find she’s as feisty as Angelina Jolie on steroids. After a dunk or two though, one quickly realises that the risk factors are minimal; with a high uniform density across its basic circular structure, the ginger nut is a firm and secure biscuit. This makes the ginger nut a fine choice for the novice dunker, with a relatively large window open to get it right.

Chocolate Digestives

The next generation of one of Britain’s most infamous biscuits; the chocolate digestive has evolved from its primitive counterpart into one of the key players of the day. A strong chocolaty exoskeleton provides the biscuit with all the support it requires for multiple dunkage, making it a wonderfully fun treat in the collection. Be warned, however, there is a darker side to the chocolate digestive. While one playfully dunks away, they may not be aware of the appending doom that awaits them; the chocolate armour that is so vital to the biscuits success is slowly melting. If melting is allowed to spiral beyond critical levels, a totally unforeseen structural collapse of cataclysmic proportions will ruin your cup of tea.

cream-of-the-year2Custard Creams:

Voted Britain’s biscuit of the year by 9 out of 10 in a survey of 7,000 people (2007), on top of withstanding over a hundred years of service in the consumer world, the custard cream certainly has a lot to say for itself. Like oxo is to instant stock, the custard cream is the classic sandwich biscuit of the biscuit world. I am sure you will be able to recall many a time spent developing the intricate techniques required to pry apart the biscuity layers from the creamy treasure that lay locked inside. The dunking experience suddenly brings the biscuits name roaring into perspective; the biscuity layers reach saturation in lightning time, revealing the creamy warm heart as it crosses your lips.

Bourbon Creams:

An elongated chocolaty mutation of the custard cream, 2010 will mark bourbon creams one hundredth year in the trade. Like a sort of no-nonsense snack, the bourbon cream doesn’t bother with a custard-cream-like ornate exterior; instead they are minimally branded with ‘BOURBON’, in the same fashion that you would label a case of dynamite. The dunking of bourbon creams can definitely be compared to that of custard creams, only naughtier and the whole experience is all a little more melt-in-the-mouth. It’s important to remember the extended length of the biscuit in comparison to custard creams, while this can prove useful in a cup-half-empty situation; the extra weight can take its toll faster than expected on those deeper dunks.

Jaffa Cakes:

Half cake, half biscuit, the jaffa cake is truly in a world of its own. From the moment that one of these peculiar creatures comes into contact with a cup of tea, the dry sponge-like base erupts into a soaking up frenzy that can only be compared to a camel at a waterhole. No matter how short the duration of the dunk, upon lifting the jaffa cake, a significant portion of your cup of tea will have disappeared. The saturated treat will literally disintegrate in the subject’s mouth, leaving an alien jelly nucleus, half liberated from its shell. Since jaffa cakes have adopted the chocolate digestive chocolate backbone system (CBS), dunkers should observe the warnings above before use.

Chocolate Chip Cookies:

The backpacker biscuit, a true traveller, the cookies journey began with the Muslim conquest of Spain from its origins in the Middle East and by the fourteenth century cookies had spread throughout Europe, across all levels of society. By the 1600s cookies had achieved a comparable feat among British and Dutch settlements in North America. The moment a choc-chip cookie breaks through the surface of a hot tea, the chocolaty nuggets explode into an erratic meltdown, bleeding their goodness deep into the biscuit’s core. Since postdunk breakup is common among cookies, the dunker should bring the biscuit to the mouth without hesitation; the dunker should now take a moment to appreciate a delicacy, 1,400 years in the making.

Jammie Dodgers:

Cue the clown, the jammie dodger has been a vital pillar in children’s parties for decades. With a basic sandwich construction, characterised by a heart shaped window that allows one to peer directly into the sensitive guts of this beauty, the jammie dodger is a wonderfully affectionate biscuit. Saying this, no amount of wiggling or nibbling will prise this monster apart; it is simply impossible to separate a jammie dodger into its constituent sandwich elements. The gluey jam adhesive is far too overpowering for the brittle shortcake counterparts and any attempt to separate the two, will certainly result in a crumby mess. A confident dunking of a jammie dodger quickly eases the bonding tension, however the shortcake composition has difficulties absorbing the tea, leaving the dunker with an undercooked biscuit and attempts to prolong the dunking will most definitely result in structural breakup.

Chocolate HobNobs:

In the words of Peter Kay, “the Steven Seagal of the biscuit world”, the chocolate hobnob is nothing short of a dunking God. Being a digestive/ flapjack hybrid, hobnobs have all of the absorbent qualities one could ask for in a digestive whilst being supported by an oaty skeletal lattice, guaranteeing a structurally sound make-up. If this isn’t enough McVitie’s pulled out the stops in 1987 and gave hobnobs a chocolate backbone; the chocolate hobnob was born. To dunk this divine creature is to be instantly transported into a new world of biscuit dunking; words won’t do, you must dunk yourself a path to higher knowledge.

The Physics

Biscuits can be described at the microscopic level as dry grains of starch held together by sugar, with a complex network of hollow channels branching throughout the biscuit. When the biscuit meets a hot liquid, such as tea, the starch molecules begin to swell and soften, in addition the tea begins to dissolve the sugar and hence the biscuit loses its structural integrity. The biscuit’s channels make it porous, giving it that great absorbing nature, which through capillary action, allows tea to be soaked throughout the biccie.

Washburn’s equation was written in 1921 and is used to describe capillary flow in porous materials. According to Dr Len Fisher, physicist at the University of Bristol, Washburn’s equation can be used to model biscuits to a high degree of accuracy.

The symbols γ and η are properties of the liquid and since we are always discussing the same liquid, tea, we needn’t worry about these. t is the time taken for the liquid to penetrate our biscuit a distance L, who has an average pore diameter D. Effectively, it is possible characterise a biscuit by its average pore diameter, the larger the pores, the faster it sucks.

By conducting the straw test it made it possible to calculate the pore size for each of the biscuits in the selection. Ranked in order from smallest pores to greatest, they are as follows: jammie dodgers, chocolate digestives, hobnobs, bourbon creams, custard creams, choc-chip cookies, ginger nuts and finally our thirsty friends, the jaffa cakes. From here Washburn’s equation is applied to each biscuit to determine the time required for the biscuit to become completely quenched.

Results of the dip, dip, dip test.

Next, the dip, dip, dip test. The red bars on the chart represent the average number of dunks required to cause a breakup, whilst the blue bars are an illustration of the unpredictability in the value of the blue bars, acting as a percentage danger factor. The higher the blue value, the more defiant the biscuit is to the extreme conditions found in a good brew. The higher the red value, the greater the stakes and the less time the dunker is given for error.

The Table of Dunkage

With all that dipping, dunking and sucking analysed, it’s finally time to unveil the all important table of dunkage.

Recommended dunking time (sec) Error margin (sec)
Ginger Nut 3 1.1
Choc Digestive 8 1.9
Custard Cream 4 0.5
Bourbon Cream 4 0.8
Jaffa Cake 2 0.3
Choc-Chip Cookie 3 1.7
Jammie Dodger 11 2.3
Choc HobNob 8 2.1
Final Thoughts

Eight varieties of biscuit and numerous cups of tea later, I can safely say I am an experienced dunker. The investigations have led me through layer after layer of bottom of the cup biscuit sludge, onto the euphoria of a perfectly soaked biccie; all this accompanied by a good dosage of laughing. Like a box of toy soldiers, each biscuit has its own character and an emotion, for instance, you don’t often find a jammie dodger sitting next to your morning tea. This all makes it very hard to judge these splendid treats and whilst some of you may disagree with my views, here are the highs and lows.

The chocolate hobnob, need I say anymore? Just how on earth such an unbelievable biscuit came into existence is baffling; the inventors are true geniuses. This bad-boy is so dedicated to the job that the gloop left behind in a breakup is nearly as tasty as the biscuit itself. Then there’s the mighty chocolate digestive, the sweet custard/bourbon creams, the jolly jammie dodgers, the delicate ginger nuts and the yummy cookies. In fact, they are all worthy dunkers, except for that is, the lonely jaffa cake, who has no friends. Whist I cannot criticise the ingenuity and architecture of these space invaders, like a city-pigeon, they are definitely not dunkers.

There may, however, be a reason for the jaffa cakes apparent loneliness, let’s take a trip back to 1991. Back then McVitie’s were challenged by Her Majesty’s Customs and Excise over a tax dispute on jaffa cakes and the case ended up before the courts. Under UK law, no VAT is charged on biscuits and cakes, although the tax is applied to biscuits of the chocolate covered variety. McVitie’s maintained that jaffa cakes were indeed cakes and so the court was soon asking exactly what criteria should separate biscuit from cake. McVitie’s argued that whilst biscuits go soft when stale, cakes should go hard and a giant jaffa cake was shown to the court to demonstrate that jaffa cakes are simply miniature cakes. Next, McVitie’s showed the Tribunal that jaffa cakes go hard when stale and with other factors in mind, McVitie’s won the case and VAT is not paid on jaffa cakes. Wrongly categorised, I owe the jaffa cake an apology.

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