Lady Tasting Tea

A statistician, a biochemist, and a phycologist walk into a teahouse…

This setup sounds like the start of a science joke. Instead, it’s a real-life scenario that showcased a potential superpower (using the term lightly) and set the stage for modern statistics.

In the early 1920s, a phycologist – someone who studies algae – named Muriel Bristol worked at the Rothamsted Experimental Station in England. Her beau and future husband, William Roach, the biochemist, and Ronald Fisher, the statistician, joined her for tea at Rothamsted.

Fisher poured a cup of tea from an urn and offered it to Bristol. Muriel eyed the cup and politely declined. She loved tea and would indeed enjoy a cupful presently, but she had spotted a problem: Fisher had added milk to the cup after the tea. Bristol stated she preferred the taste better when milk hit the porcelain first.

The statistician found this claim to be absurd. How could anyone tell the difference between the two methods of preparation? Surely, the chemical output would be the same?

Instead of romantically backing Bristol, Roach immediately exclaimed, “Let’s test her!”

And so began one of the most famous experiments in quantatative science history, known now as lady tasting tea and described in Fisher’s revolutionary 1935 book The Design of Experiments.

With Roach’s help, Fisher prepared eight cups of tea, four of each milk-tea ordering. They presented the cups to Bristol, telling her to identify which cups had been prepared which way.

This simple examination altered the course of statistics and scientific rigor in studies. Fisher approached the test with the belief in the null hypothesis, namely that he felt Bristol was up to her eyes in milk. He wondered about several key aspects that are now commonplace in such studies. How could they present the tea randomly to prevent any possible foreknowledge to Bristol, other than her supposed ability to taste the difference? And how many cups would be needed to display with confidence that she had not simply guessed correctly by chance?

With eight cups, as it turns out, the chance of randomly nailing the right answers is 1 in 70 or about 1.4%. To Fisher, only a result of eight for eight would reject the null hypothesis. Importantly, if Bristol aced the test, it would not necessarily prove her claim but it would render the lucky guess to a low probability.

To everyone’s astonishment, Bristol separated the cups into perfect groups.

Though Fisher had possibly just interacted with a human with super abilities, he focused on the implications of the statistics.

From this seed, he developed Fisher’s exact test, which helped formalize and popularize contingency tables and statistical significance. Further, the influence on blind or randomized testing was profound. What variables should a proper test use to minimize the potential for guessing or, worse, the mechanations of a charlatan? In the instance of tea, should the tester vary temperatures or sweetness? How could the quality and strength of the tea be maintained across cups? How many cups would be needed for the exercise to be statistically significant? In what order should the cups be presented to the subject? Even further, supposing the subject did have the stated ability, how could the tester incorporate a potential mistake from falilble humans?

After Fisher’s book, in which he recounted this performance by Bristol, these practices, calculations, and thought processes became the scientific norm. Quite a consequential round of tea!

As fascinating as this impact on statistics and testing is, has history buried the real wonder of lady tasting tea?

How could Muriel Bristol know which cup was poured with tea or milk first?

Studies have suggested – and likely under the influence of Fisher! – that wine tasters, for example, cannot distinguish things they claim to taste. Did Bristol just get lucky?

The English regard their tea very seriously. Debates have raged for centuries on the proper ordering of milk and the brewed fineries. In 1946, George Orwell published “A Nice Cup of Tea” in which he laid out eleven rules he considered “golden.” Some historical research suggests milk was origianlly added to china first because the drinkware could not withstand repeated exposure to boiling water. Then, at some point, the higher classes began switching the timing, signaling that they could afford to lose their porcelain cups. Weird flex!

Either way, can the taste possibly be different?

Unfortunately, no definitive scientific answer currently exists. A few studies claim two possibilities. The first relates to tannins in tea, the chemical compounds that impart bitter taste. The amount and intensity of tannins might vary with the temerpature curve of the drink. Boiling tea hitting a cup does not cool at the same rate as boiling tea hitting a cooler liquid. A discerning palette might be able to distinguish the difference in tannin levels. The second hypothesis revolves around the denaturation of proteins in milk. When boiling water hits these proteins, they break down. If hot tea hits a chaucer with milk, it affects the milk as a whole. However, often, milk is added in drops when done the other way. These little blubs of milk encounter scalding water and become denatured more easily. Could the method of adding milk in a stream cause the flavor to change through denaturation?

The tea-time jury is out.

A fun hypothetical poses potential superpowers that seem underwhelming or have only minor consequences on the world. Being able to distinguish the order in which tea and milk were added to a cup seems to fit. A tongue that can detect subtle alterations in milk proteins or tannins might not be able to save the planet, but it can be a nice party trick.

Only Muriel Bristol’s magic trick doesn’t seem to have been hypothetical at all!

BONUS: Though Muriel Bristol is now known for her tea-tasting prowess, she is also immortalized through her work with algae. The species Chlamydomonas muriella bears her name!