The Last Word has long been dedicated to discovering the science of , so maybe you can help. I’ve read in many places that when the vodka and vermouth that make up the martini are being stirred with ice you should always use a proper long, thin bar spoon, or failing that a table knife. This makes for a much colder drink than stirring with a normal, wide-bowl spoon. I tested this, stirring two identical martinis for 30 seconds, and found the martini stirred with the knife was an average 2.5 °C while that with a tablespoon was 3.9 °C. I repeated the experiment five times (on different nights, honestly). So why?
• As Q might say: “The effect of the stirring device on the final temperature of the martini depends on how much heat the stirrer adds (or removes) from the mix. Oh, do pay attention 007.”
A stirrer with a large mass will have a bigger potential effect than a small one. This may be one reason why “proper” bar spoons are long and thin, although I suspect it may also be to reach the bottom of tall glasses or cocktail shakers. A tablespoon would certainly have a bigger warming effect than a knife, assuming both implements initially were at the same temperature and warmer than the drink.
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The rate of heat transfer from stirring implement to drink depends on the thermal conductivity of the implement. Thermal conductivity varies quite widely between metals; a solid silver spoon would conduct heat about 16 times as fast as a stainless steel spoon. Heat would be conducted from the mass of spoon immersed in the drink, but it would also flow from the shaft and thus from the barman’s hand. This effect would be smaller the thinner and longer the shaft, which may be another reason for the shape of bar spoons.
The amount of heat available for transfer from the spoon to the liquid depends on how much warmer the spoon is than the liquid and on the specific heat capacity of the spoon. For metals, specific heat capacity does not vary quite as much as thermal conductivity – it’s about twice as high for stainless steel as for silver. It also depends on the shape of the implement, but since the business ends of both spoons and knives are essentially thin plates they would not differ much in this respect.
Q’s recommendation, were he to bother with such trivia, would be to use a wooden spoon, ideally one of the long thin paddles sometimes provided with takeaway hot drinks. Wood generally has a specific heat capacity of the same order as metal, but a very much lower thermal conductivity. Softwoods generally have lower thermal conductivities and capacities than hardwoods. Q might also recommend cooling the spoon and wearing gloves. He would certainly advise against employing a gold finger.
“Q’s recommendation, were he to bother with such trivia, would be to use a wooden spoon”
John Gee, Aberystwyth, Dyfed, UK
• A normal spoon’s wider bowl moves more of the martini against the inner surface of the cocktail shaker. Accordingly heat from the air is conducted more efficiently via the shaker to the drink. Stirring with a spoon is also likely to result in more of the liquid riding high up the inner surface of the glass’s cone-shaped bowl.
Still, the case is not closed. Attention to scientific detail demands that the phenomenon be subject to further investigation and any speculation eliminated. You could try repeating with plastic cutlery or wearing heatproof gloves. Good luck.
Len Winokur, Leeds, UK
• I can think of at least five ways that stirring a martini with a wide-bowl spoon could result in a higher temperature drink than using a long, thin bar spoon. First there is the question of simple calorimetry. Assuming the spoon is at room temperature, it will contain a certain amount of heat: a function of its mass, temperature and specific heat capacity, which is quite high for metals, compared with plastic or wood. It will contain more heat than a lighter, metal bar spoon.
Second, because it has a larger surface area it will conduct this heat more quickly into the drink and third – for the same reason – more heat will also be conducted from the warm hand via the wide-bowl spoon compared with the bar spoon.
“Because a normal spoon has a larger surface area it will conduct heat more quickly than a bar spoon”
The fourth factor is the shear applied by the larger wide-bowl spoon during mixing, which will also add more heat to the system.
Finally, the more turbulent flow caused by stirring with the wide-bowl spoon will tend to draw more warm air into the drink, further increasing the temperature. If you don’t have a bar spoon handy when making that martini, try stirring with a pencil, which has less surface area, less mass, a lower specific heat and will, therefore, conduct less heat from the hand.
Mark Wareing, Halkyn, Flintshire, UK