1. Discussion with David Nepov: Shawn writes

On June 3rd, 2016 - Shawn wrote:

Hi David, 

I want to make sure I'm not teaching the wrong thing, and I'd like your help - whenever it may become convenient.  I've been teaching that the “reason for shaking citrus” is due to the need to “integrate acidity”. Why? Background:

  1. Cooking Issues 2009 article Science of Shaking inspired me. 
    1. With friends from UC Berkeley's chemistry lab, I took the concept of reaching Thermal Equilibrium (Dave Arnold, Cooking Issues), and cross-referenced it with Citrus Juice (weak acid carboxylic) reactions in ethanol.
    2. My UCB chemistry students, used “temperature vs. dilution” data from Cooking Issues­­. They acknowledge although acidy à ethanol “carboxylic reactions” generally need a catalyst (like a strong acid), and/or heat/time - a small amount (several parts per million in esters) should be produced from shaking the acid. And furthermore they said the reaction may not not occur if the cocktail has already gotten too cold/dilute – I.e. thermal equilibrium as already been reached.
  2. Still, the UCB graduates had trouble believing these small amounts of esters were discernible by human taste. So I consulted with my mother in law, who is a sensory scientist. She indicated the small differences in the ester in question, Trethyl Citrate, formed from shaking acidity are well within the range of discernible taste sensitivities. I then attempted to confirm this through my own research.
  3. In 2010, feeling confident in my findings, I started, and have been, teaching this very thing for the past 6 years: Hydrogen Donation and Esterification as the main reason one would shake acidity (i.e. citrus juice). In other words, the need to integrate acidity before it gets too cold and dilute – which is thought to reduce the energy needed for the small amount of esterification to occur. 

Since then, having been mired in the world of opening and running businesses, I've not kept up with newer research. However, having opened a new bartending school, I've found it necessary to update my knowledge.  Needless to say, I was quite surprised to find Shaking vs. Stirring research has gone a different direction. The general consensus now from such bodies as the MIT, Royal Society of Chemistry, and several other notable universities, seems to point to things like Oxidation of Aldehydes, reduction of Hydrogen Peroxide, and a general difference in texture as the main reasons you shake. 

Indeed, there's not even 1 article I can find, scientific or otherwise, which even mentions esterification. Hence, my contacting you to get your opinion. Am I completely off the mark here, or has the industry not considered the possibility of Acidity as a hydrogen donator? If oxidation is the main culprit, then would it not be easy to simply chill & dilute a citrus cocktail, only to dry shake before serving? Would it not also be equally okay to add the forgotten lime juice to an already shaken drink and re-shake? Is it confirmation bias, which inform me these processes fall short of producing the ideal drink? 

Looking at the trend, the following seems possible to me:

1.    Cooking Issues people acknowledge that although Thermal Equilibrium is reached in 12 seconds regardless of ice type and shake vigorosity, there my very well be differences in texture. This controversy about differences in texture as a follow up to the original experiment became a hot topic, and led to the subsequent 2010 experiment from Cooking Issues. This follow up, which tested textural difference as a function of aeration - caused by shaking - began with a-priori assumption that this could be the only other difference in people’s preference for shaking citrus cocktails. I think it’s possible esterification was not even considered. It appears since the follow up Cooking Issues article, this assumption about texture and aeration has become the standard in considering the reasons for shaking vs. stirring.

Any feedback would be appreciated. Or, if you can point me to someone who can help, I would very much appreciate it, as would all my future students. 

Thank you

Shawn RefouaComment