## 4 Discussion
### Gc-Ms
Medium-chain fatty acid ethyl esters, such as ethyl octanoate (caprylate), and ethyl decanoate (caprate), are traditionally found in lambic and gueuze beers. These ethyl esters are normally absent in lagers and present in only small concentrations in ales [26; 38]. Both ethyl caprylate and ethyl caprate are considered to be typical aroma and flavor compounds of lambic and gueuze beer. Ethyl octanoate as well as ethyl decanoate were identified in all of the aging lambic beer samples using GC-MS but they were not identified by the panelists via GC-O. Individually, these compounds could be present below the threshold level; however, when combined, these compounds could both be perceived. This was unexpected since ethyl hexanoate, ethyl octanoate, and ethyl decanoate give lambic and gueuze beer its wine and fruity flavor [13; 39]. The secondary byproducts produced by the wild yeast strain _Brettanomyces_ play a greater role in the aroma and flavor profile of lambic beer than traditional brewer's yeast, _Saccharomyces_. The main chemical compounds produced by _Brettanomyces_ are the esters, ethyl acetate and ethyl lactate. Ethyl acetate and ethyl lactate can be formed enzymatically or chemically. Esterase is the enzyme used in the chemical reaction between ethanol and an organic acid to produce these esters. _Brettanomyces_ displays a higher esterase activity than other yeasts (_Saccharomyces_ or _Hanseniispora_) [33]. _Brettanomyces_ has been linked to the synthesis of ethylphenols (4-ethylphenol and 4-ethylguaiacol) and vinylphenols [40]. Brett is currently the only known microorganism linked to the development of ethylphenols. Some species of lactic acid have been known to produce ethylphenols in media but not in actual beverage systems [41]. _Brettanomyces_ is a key player in the sensory profile of lambic and gueuze beer [2; 42]. The \"bretty\" character is associated with a number of different aromas and flavors, such as mineral, tobacco, barnyard, leather, pharmaceutical and smoky [20; 24]. Compounds produced by _Brettanomyces_ have the ability to suppress a number of the desirable fruity ester aromas [43; 44]. The horsey aroma can vary from slight to very strong. The strength of the horsey aroma is dependent upon the fermentation conditions; tetrahydropropylidines are the compounds associated with the horsy smell. Tetrahydropyidines are produced from ethanol and the amino acid lysine from the wort [14; 45]. Although 4-ethylphenol was found in all of the samples using GC-MS, it was not detectable by the panelists until the six-month sample. This is not surprising since _Brettanomyces_, although present in the beer early on, does not typically start producing detectable by-products (4-ethylphenol and 4-ethylguaiacol) until after the primary fermentation (_Saccharomyces_) has been completed [1]. Alcohols are produced as a byproduct of yeast metabolism. The concentrations of higher alcohols in lambic beers and other styles of beer are similar. Ethanol is just one of several alcohols that can be found in lambic along with higher alcohols (fusel alcohols), which are considered important by products of fermentation. Similar to ethanol and fusel alcohols, other alcohols are also produced during the main fermentation stage [21]. Based upon a study by [PERSON], it was determined that a number of different alcohols can contribute to the flavor of beer: iso-amyl, phenethyl, propyl, and iso-amyl alcohol (2-methylbutanol) [46]. The higher alcohols identified do play an important role not only in the flavor of the beer, but also in the production of ester compounds as well. Lambic and gueuze are well known for their high levels of acidity. It has been reported that gueuze has a lactic acid concentration of 1500-3400 ppm and acetic acid had a concentration of approximately 700-1200 ppm [1]. [PERSON] et al. has found similar results based off of the commercial samples that where analyzed [7]. Ales and lagers have much lower acetic and lactic acid concentrations than gueuze beer.