Tuesday 23 February 2010

Flavour compound of the Week - Iso amyl ethanoate

Iso amyl ethanoate, also known as isopentyl acetate, banana oil, isopentyl ethanoate, pear essence, 3-methylbutyl acetate and 3-methylbutyl ethanoate is a bit confusing really. It’s known in brewing as both the pear drop ester and a banana ester. How can it be both? Well that depends on what else is going on flavour-wise and the concentration of the ester. In confectionary it is used to make both pear drops and banana sweets.

Iso amyl ethanoate (pronounced eye so A mile ee fan oh 8) is produced in fermentation by yeast metabolism. The mechanism of ester production and control is very complicated and linked to yeast growth. I won’t try to explain because I haven’t got time to get my text books out and it would make tedious reading. Strong worts and warm fermentations tend to lead to higher levels of esters in the beer. Again yeast strain is important. Yeast used in Belgian beers tend to be much more ‘estery’ than UK beers. Lager type yeast produce very low levels of esters when compared to ale strains.

Iso amyl ethanoate is also a bee hormone. It is secreted by the sting of a bee when it is deployed to encourage other bees to get stinging. Not therefore a good choice for a fragrance for lip balm or hemorrhoid cream.


Kieran Haslett-Moore said...

"Lager type yeast strains produce very low levels of esters"

Except when they are opperated in high gravity continuous fermentation systems as we see here with DB.

Stuart Howe said...

Thanks Kieran,

The sentence I used is "Lager type yeast produce very low levels of esters when compared to ale strains." This relationship will be the same regardless of style of fermentation. An ale type yeast would produce more esters than a lager type in the same type of continuous fermentation.

As ester production is linked to yeast growth continuous fermentations will give more esters because yeast growth is inevitable in that system.

Most yeast used in modern (high gravity/high hydrostatic head/continuous)style fermentations are either hybrids or are modified in some way to enable them to survive the extreme conditions in fast-rate high-volume fermentations.

What DB us is probably not a classic lager or ale strain.

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