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Other intermediate flavor and aroma compounds are creating during the fermentation process. For example, De Roos et al. (2018) reported the production of acetoin from week 3 to month 6 in lambic beers, and then a gradual decline after that. This corresponded with the growth of acetic acid bacteria (AAB), and the production of acetoin was attributed to the AAB oxidizing lactic acid. 2,3-Butanediol and 2,3-butanedione (diacetyl) were not found during the entire age of the lambics studied, so the full conversion of acetoin to these compounds never occurred. The decline of acetoin during the maturation phase was attributed to ''Brettanomyces'', which is known to occur when oxygen is limited. Malic acid was depleted as the lactic acid bacteria started to grow from month 6-9, and lactic acid increased (both D-lactic acid and L-lactic acid in nearly equal amounts at around 2.0 g/l), indicating malolactic fermentation occurred during this time. After the acidification phase and during the maturation phase where ''Brettanomyces'' and ''Pichia membranifaciens'' were dominant, small amounts of malic acid were produced, indicating that these yeasts are capable of producing small amounts of malic acid (less than 20 mg/l of malic acid was in the lambic beer at 24 months). Gluconic acid and citric acid, which were presumably introduced from the brewing process, were present at fairly stable levels during the entire fermentation process, with gluconic acid seeing a slight spike during the growth of acetic acid bacteria (~50 mg/l and ~220 mg/l in the final beers) <ref name="Roos_2018_2" />. As bottles of packaged beer age, they tend to increase in lactic acid and ethyl lactate concentrations as years pass, which also corresponds with a slow decrease in dextrins <ref name="Spitaels_2015_Bottles">[https://www.sciencedirect.com/science/article/pii/S0740002014002548 Microbiota and metabolites of aged bottled gueuze beers converge to the same composition. Freek Spitaels, Simon Van Kerrebroeck, Anneleen D. Wieme, Isabel Snauwaert, Maarten Aerts, Anita Van Landschoot, Luc De Vuyst, Peter Vandamme. 2015.]</ref>.
Below is a collection of data on spontaneously fermented beer sampled from bottles available in the market; see the data sources for standard deviations, methodology, etc.; a dash (-) means not reported or measured:
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Reported volatile compounds in mg/L; a dash (-) means not reported or measured:
{| class="wikitable sortable"
| Cantillon Gueuze; Bottled 2013, Bottle 2 || - || - || - || - || - || 11.8 || - || 44 || 163 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
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| Cantillon Gueuze; Bottled 2013, Bottle 3 || - || - || - || - || - || 11.3 || - || 195 || 130 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
|-
| Cantillon Gueuze; Bottled 2011, Bottle 1 || - || - || - || - || - || 3.3 || - || 166 || 170 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
|-
| Cantillon Gueuze; Bottled 2011, Bottle 2 || - || - || - || - || - || 8.7 || - || 175 || 252 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
|-
| Cantillon Gueuze; Bottled 2011, Bottle 3 || - || - || - || - || - || 7.5 || - || 162 || 292 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
|-
| Cantillon Gueuze; Bottled 2010, Bottle 1 || - || - || - || - || - || 2.9 || - || 249 || 203 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
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| Cantillon Gueuze; Bottled 2010, Bottle 2 || - || - || - || - || - || 8.2 || - || 295 || 283 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
|-
| Cantillon Gueuze; Bottled 2010, Bottle 3 || - || - || - || - || - || 6.5 || - || 332 || 285 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
|-
| Cantillon Gueuze; Bottled 2008, Bottle 1 || - || - || - || - || - || 2.2 || - || 371 || 125 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
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| Cantillon Gueuze; Bottled 2008, Bottle 2 || - || - || - || - || - || 5.7 || - || 413 || 319 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
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| Cantillon Gueuze; Bottled 2008, Bottle 3 || - || - || - || - || - || 5.6 || - || 415 || 246 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
|-
| Cantillon Gueuze; Bottled 2004, Bottle 1 || - || - || - || - || - || 2.0 || - || 630 || 140 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
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| Cantillon Gueuze; Bottled 2004, Bottle 2 || - || - || - || - || - || 3.4 || - || 592 || 197 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
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| Cantillon Gueuze; Bottled 2004, Bottle 3 || - || - || - || - || - || 2.7 || - || 464 || 178 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
|-
| Cantillon Gueuze; Bottled 1996, Bottle 1 || - || - || - || - || - || 1.8 || - || 526 || 89 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
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| Cantillon Gueuze; Bottled 1996, Bottle 2 || - || - || - || - || - || 3.9 || - || 778 || 150 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
|-
| Cantillon Gueuze; Bottled 1996, Bottle 3 || - || - || - || - || - || 2.5 || - || 556 || 169 || Spitaels et al. (2015) <ref name="Spitaels_2015_Bottles" />
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