The Aroma Files #004: Pineapple
Pineapple is one of the most intriguing beer aromas. Even more fascinating is that while fresh, canned, and dried pineapple all have different and progressive aromas, so do the pineapple aromas in beer. Lets first explore the varying components making up the pineapple aromas in the fruit and its derivatives.
Fresh pineapple can be described as bright, tropical, and lightly sulfuric. The key component here is ethyl butyrate, which is the classic pineapple ester. Another ester, methyl hexanoate, adds some fruity top notes while two volatile sulfur compounds, methyl mercaptan and ethyl sulphide add that light sulfury tropical character.
In canned pineapple, the packaging process triggers some changes in composition. The heating produces some light maillard products like foraneol and a few caramelizations, giving a kind of cooked fruit quality. 5-Hydroxymethylfurfural from the dehydration of the sugars adds a bit more caramel, and the breakdown of certain lipids results in γ- and δ-lactones which lend a faint coconut aroma. The process also hydrolyzes certain esters. Specifically, the breakdown of ethyl butyrate and methyl hexanoate reduces those bright pineapple notes. On top of it all, some diacetyl can make its way in there adding a touch of butteryness to the whole picture.
Dried pineapple results in the further concentration of sugars and acids, but a lot of the esters and thiols are oxidized and destroyed along the way, reducing the fruity and tropical notes. Similar to canned pineapple, foraneol and 5-Hydroxymethylfurfural come into play, as does γ-decalactone. More interesting though, is the development of certain aldehydes. Hexanal and (E)-2-Hexanal from lipid oxidation add a slight fatty perception, while benzaldehyde from maillard reactions adds an almond like flavour, and phenylacetaldehyde from amino acid degradation adds honey notes.
Moving over to the beer, the pineapple flavour and aroma is a function of multiple components, including certain esters, terpenes, thiols, and lactones.
The Esters
The textbook pineapple ester is ethyl butyrate, and in beer it is manufactured by the yeast via the esterification of butyric acid and ethanol. This ester is abundant in pineapple juice and is also used to flavour pineapple candy. Ethyl Hexanoate has a kind of pineapple/apple sweet fruit aroma, and ethyl acetate, although quite solventy at higher levels, can add a fruityness to the bouquet. Isoamyl acetate tends to sneak its way in as well. That’s the signature banana ester common in weissbiers, but in combination and at lower levels it really just boosts the fruit percetption. In situations involving warmer ferments, and especially in NEIPAs, the ester ethyl-2-methylbutyrate can add extremely potent pineapple and tropical notes.
The Terpenes
The terpenes play more of a supportive role than a starring role. Linalool and citronellol can have some tropical notes, and both β-pinene and limonene can enhance the pineapple character.
Lactones
While both very nuanced, γ-decalactone and δ-decalactone, from heat treated malt, or from aging, can add a slight pineapple quality.
Thiols
Thiols need to be present in the hops in a bound form to then be released by the yeasts, and so the presence in the finished product is two-fold. This process is dependent on the yeast being thiol positive, that is coded for the production of certain enzymes that break off the sulfhydryl group. The thiol 3-mercaptohexanol (3MH) is the pineapple-passionfruit aroma, and 3-mercaptohexyl acetate (3MHA) the esterified version of 3MH is even more aggressive.
Warmer fermentation conditions, and higher ester yeast strains will push up the pineapple character, as will lower oxygen and/or high available fatty acids. Yeast that are thiol positive, of course, can unlock some thiols from various hop compounds via dry hopping.
The super pineapple aroma combo is ethyl butyrate, linalool and citronellol, and 3MHA.
And Now the Exciting part
The real fun though, is that the pineapple aroma can not only differ in various beers, but can even shift down the flavour gradient in the same beer. Now to be clear, this is not entirely desired, so we are viewing this from the perspective of the beer student rather than the disappointed patron.
When the beer is at its freshest, the esters, thiols and terpenes remain intact, but after a few months the esters and thiols begin to break down via hydrolysis. Ethyl butyrate and ethyl hexanoate for example, begin to slowly revert back to alcohols and acids. 3MHA hydrolyzes back to 3MH losing some of its pungency. Linalool and citronellol oxidize, and while most of their aroma profile remains intact, the sensory threshold increases, reducing overall perceived contribution.
On top of all this, the general oxidation of the beer can push the perception of canned vs fresh fruit.
As time continues, most of the esters have degraded, some alcohols have oxidized to aldehydes and acids, and the complete degradation of thiols results in a total loss of the juicy, tropical edge. Now we have beer that reminds us more of dried pineapple, than the bright juicy fresh fruit.
While our focus was on the why of pineapple aromas, remember to keep and drink your beer fresh!
To further hone your aroma identification skills, Master Cicerone® Jen Blair’ ‘s Aroma: Explore The Wheel offers 100 common beer aromas! https://underthejenfluence.beer/
Four down, four-hundred to go!