First I was very surprised to see that the term ‘drinkability’ seems to have been coined by a Brazilian PhD student, Rubens Mattos, as recently as 2004. Apparently it caused a lot of excitement in the brewing industry and lead to the symposium. In the introduction to Mattos's paper on drinkability he said:
He was at the symposium in 2006 where he defined drinkability as:“a beer that has good drinkability is one that invites the drinker to another glass.”
“a measure of how enjoyable and attractive a beer is in order to be consumed in large quantities”.
The large quantities part is important, and many a beer nerds seems to confuse ‘drinkability’ with enjoyability, and consider any beer they like to be drinkable. Mattos considers drinkability to be:
“ a characteristic that prevents consumers from being satiated even when large volumes have been consumed.”
In more detail (he was doing a PhD after all) Mattos considers drinkability to be composed of four factors: sensory and cognitive effects, and post-ingestive and post-absorptive responses.
The next up at the symposium was, David Thompson, who spoke on the psychology of drinking. He equated drinkability with sessionability (it would seem the term ‘sessionability’ was in use already). Sessionability was defined as:
“asking the barman, ‘same again, please’”
Again, the consumption of volume is clearly important so those of you that say Imperial Russian Stouts have great drinkability, or that you can session Double IPAs, you're wrong.
Keith Greenhoff from a market research company also equated drinkability with sessionability when he spoke and his definition was:
“an absence of characteristics limiting consumption in volume, making it easy to drink.”
These characteristics included high carbonation, increasing bitterness and excessive sweetness. A definite point there for those that say cask beer has the greatest drinkability, with high carbonation being a negative factor.
A more positive drinkability definition was given by another student Katrin Mathmann as:
“drinkability means the drink agrees with the consumer and encourages the consumer to keep on drinking.”
There's perhaps not a dictionary definition from the symposium. But I think the key points are covered, and it's clear that serving beer as god intented, without extraneous carbon dioxide, gives the best drinkability.