Microbiology and Biochemistry: Difference between revisions
| Line 64: | Line 64: | ||
While oxidation can occur rapidly due to a break in the fidelity of the seal at the cork, oxidation can still occur without the passage of oxygen through the cork or significant oxygen gas in the headspace due to the transfer of oxygen from an oxygen-containing compound like ____ or ____ in the wort to others. The act of losing an oxygen, or more generally, of losing electrons, is called reduction. Reduction of ____ by ____ to (E)-2-nonenal (as well as other linear aldehydes) has been implicated as being of primary importance to the long-term oxidation of flavor compounds in beer,<ref name=Jamieson > A. M. Jamieson, E. C. Chen, and J. E. A. Van Gheluwe, A study of the cardboard flavour in beer by gas chromatography, [http://www.asbcnet.org/publications/journal/Pages/default.aspx | Proceedings of the American Society of Brewing Chemists], 1969</ref> which leads to a characteristic flavor of oxidized beer, commonly described as being of "wet cardboard". However, many other processes and compounds are important to the ageing of beer as well. | While oxidation can occur rapidly due to a break in the fidelity of the seal at the cork, oxidation can still occur without the passage of oxygen through the cork or significant oxygen gas in the headspace due to the transfer of oxygen from an oxygen-containing compound like ____ or ____ in the wort to others. The act of losing an oxygen, or more generally, of losing electrons, is called reduction. Reduction of ____ by ____ to (E)-2-nonenal (as well as other linear aldehydes) has been implicated as being of primary importance to the long-term oxidation of flavor compounds in beer,<ref name=Jamieson > A. M. Jamieson, E. C. Chen, and J. E. A. Van Gheluwe, A study of the cardboard flavour in beer by gas chromatography, [http://www.asbcnet.org/publications/journal/Pages/default.aspx | Proceedings of the American Society of Brewing Chemists], 1969</ref> which leads to a characteristic flavor of oxidized beer, commonly described as being of "wet cardboard". However, many other processes and compounds are important to the ageing of beer as well. | ||
The Mailard reaction, also responsible for the browning of toast and steak among many other things, | The Mailard reaction, also responsible for the browning of toast and steak among many other things, occurs in the unfermented reducing sugars left in the beer during extended ageing, leading to a darker brown color as well as a slight "burnt toast" flavor.<ref name=Vanderhaegen1> B. Vanderhaegen, H. Neven, H. Verachtert, G. Derdelinckx [http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCAQFjAA&url=http%3A%2F%2Fwww.researchgate.net%2Fprofile%2FGuy_Derdelinckx%2Fpublication%2F222839054_The_chemistry_of_beer_aging__a_critical_review%2Flinks%2F0c960523339c4b25a6000000.pdf&ei=Tq3IVKmfFcGyogSs_YLQCA&usg=AFQjCNFaBrvqDGjqEV2I9uQ73dYh_ParXg&sig2=Z8dY4iDHozbT1eb9JeAdrw&bvm=bv.84607526,d.cGU| The chemistry of beer aging – a critical review], 2006</ref> | ||
Many other reactions occur as Lambic ages that are not elaborated upon here in the interests of brevity. | |||
=Sources of the microbes in Lambic= | =Sources of the microbes in Lambic= | ||