Charles Perry > wrote in message >...
> Ivan McDonagh wrote:
>
> > As the subject indicates, I'm a bit concerned about the smell of my
> > starter.
>
> Don't worry about it. It is a natural thing that happens. It is only unusual
> in the sense that you report the smell from starter that you are using more
> often. I have only noticed that smell in starter that seriously needed to be
> fed. I am thinking about a covered jar of starter that had been pushed to the
> back of the refrigerator and forgotten for a time.
>
> I think of a starch, to sugar, to alcohol, to vinegar progression as the basic
> chemistry in the yeast culture. However, acetone and aromatic esters are, or
> can be produced as well. In a very active culture, the areation caused by the
> CO2 bubbling should disapate the minor areomatics before they can accumulate in
> noticable quanities.
>
Paint thinner smell ?
It is likely the ester, ethyl acetate , the esterification reaction of
the alcohol formed by the yeast and the acetic acid formed by the
lactobacteria
CH3CH2OH + CH3COOH = CH3CH2COOCH3 + H2O

It is volatile substance and that material is the predominating smell
of ripe banana flavor so its not toxic at such very small quantities.
Roy