Does gin "bruise"?

According to some, aerating the gin by splashing it around alters the flavor, or "bruises" it; or more perceptibly, one would be likely to quickly notice the little bubbles disrupt its normal tongue/palate texture.

From Wikipedia, "Shaken, not stirred":

Some connoisseurs believe that shaking gin is a faux pas, supposedly because the shaking "bruises" the gin (a term referring to a slight bitter taste that can allegedly occur when gin is shaken). In Fleming's novel Casino Royale, it is stated that Bond "watched as the deep glass became frosted with the pale golden drink, slightly aerated by the bruising of the shaker," suggesting that Bond was requesting it shaken because of the vodka it contained. Prior to the 1960s, vodka was, for the most part, refined from potatoes (usually cheaper brands). This element made the vodka oily. To disperse the oil, Bond ordered his martinis shaken; thus, in the same scene where he orders the martini, he tells the barman about how vodka made from grain rather than potatoes makes his drink even better.

Better, from the Martini FAQ;

...while we should all defer to the inimitable Mr. Bond on matters such as high-tech spy gadgets, impromptu hand-to-hand combat, and retrograde seduction techniques, his reasoning on this matter is specious. To "bruise" a wine or spirit means to take some action that changes its taste. Agitating and therefore aerating a gin or vodka martini changes its taste: it makes it taste "sharper". It imparts a certain bite or zing. Given this, and given his dislike of a bruised spirit, Bond should insist that his drink be "Stirred, not shaken," since shaking "bruises" the gin more than stirring does.

...Here are the facts: Shaking cools a drink more quickly. Shaking is more likely to chip small shards off the ice, some of which will make their way into the drink, no matter how carefully one strains and pours. Which may be part of the reason why... Although the gin spends less time with the ice when the drink is shaken, shaking a drink actually dilutes it more than stirring does. Very rarely, shaking can produce a chill haze (the precipitation of very small solid particles) from the vermouth, giving the drink a cloudy appearance. Shaking creates tiny bubbles in the mix, which temporarily impart a cloudy appearance to the drink. Shaking causes a certain class of molecules in the liquor (aldehydes) to combine with oxygen more than stirring does. The oxidation of these molecules also slightly alters the flavor, making it "sharper" (Miller, Anistatia R. and Jared M. Brown. Shaken Not Stirred: A Celebration of the Martini. New York: HarperCollins, 1997).

Shaking gin releases oils found in the juniper berry and produces a little sharper or bruised taste

The concept of bruising gin is equal parts truth, and nonsense. Truth in that it does somewhat alter if not the taste per se, then at least how it rests on the palate. nonsense because really, of all the words we could use to describe this effect... aerating, berating, incloudulating... 'bruising' seems to be the tossiest.

There are certain cocktail which I feel benefit from a severely 'bruised' gin. A Last Word, for example, or indeed any of the so-called 'corpse revivers'. Those drinks I like cloudy, sharp, and punchy. A Martini, on the other hand, should be made thus:

Chilled to within an inch of sanity, by way of pre-chilling the gin (only necessary in hotter climes), pre-icing the class AND garnish, and of course stirring with ice. The resultant beverage should be so crystal (from lack of shaking and more importantly from lack of Vermouth), that one can clearly see through it - to the bartender - who is dutifully making your second round. And YOU, dear sir, should tip that bastard generously. He has a beard to feed.

"Don"t bruise the Gin" is a very old request. It is NOT caused by shaking but by stirring the Gin. Prior to stainless steel, bar spoons were made from iron, steel or silver. Both iron and steel spoons will rust if not cleaned and dried properly. If the bartender stirred your Gin with a spoon that had rust on it it would change the color and taste of the Gin which was referred to as bruising. Hence, shaken NOT stirred prevented bruising the Gin.

This is one of those things that everybody has an answer for, but nobody has any evidence.

Almost nobody. The website Proof66 decided they were uniquely qualified to provide some actual... evidence. They did a controlled, blind-tasted experiment with 4 different ways of beating up the Gin. Check it out.

The bottom line on the question "Can you bruise a gin?":

Nope, it's complete bullshit. The only difference is a little in the presentation and the potential dilution of ice.

Now let's note two interesting pieces of context from our other answers here, as it may well be that it was once possible to bruise gin, but is no longer:

1. If, once upon a time, gin tended to have material amounts of oil in it, you're now talking about a different animal, in both chemistry and texture. It could have had very different characteristics than today's gins. The experiment I've cited doesn't address that.

2. If people were once in the habit of dipping highly-reactive metals into a drink (particularly one packed with volatile oils) in order to stir it, then yes, that certainly could have changed the flavor as well.

So, to say that 'bruising' of gin is a non-operative concept today is not to say that it was never an operative concept, particularly all the way back when the first Bond books were written, which was a very, very different era in terms of food & beverage production. But unless someone has other actual evidence - from either chemical theory or from controlled experimentation - it seems to be non-operative in today's context. (At least with gins made in the style of Tanqueray, which is admittedly a very commercial, very mass-produced product.)

Further, to say that 'bruising' is a non-operative concept is not to say that a vigorously-shaken martini can't taste rather different than one that is gently stirred. But again, this seems to have everything to do with ice-crystals and dilution, for which it's possible to control, and little to do with 'tossy' concepts like 'bruising'.

Science.

https://talesofthecocktail.com/techniques/scientific-argument-never-shaking-your-gin

“Any complex mixture of odors is generally divided into three parts: top note (in perfumes this is also known as the head note), middle note (heart note) and base note or fixative,” Stewart said.

[...]

In gin, the most distinct and attractive notes are the lovely juniper and coriander. It’s what makes gin so enticing.

“This is the top note,” Stewart said. “And the quality of juniper actually doesn’t come from a single compound, but rather a mix of lightweight alcohols.”

So when you agitate gin — say by shaking it for a martini — you’re causing the top notes to dissipate. Those bits of pine and botanicals that you look forward to start breaking down and become dull. The end result: A cocktail that’s nowhere near as crisp as it should be.

“This is what we call bruising,” Stewart said. “Once you’ve shaken it, the rest of the drink only contains middle and base notes. Yuck.”

The earliest reference I can find to 'bruising the gin' is in Casino Royale, and that's Bond referring to the drink, made the way Bond wanted it. When I read the passage I don't see it as a negative.

Regarding oils, 90% of martini's end up with the oils from a zest on top of the drink so I hardly think the oils from the spirit are going to make a difference to mouth feel with this on top.