Changes

While most beer styles are fermented using a monoculture of ''Saccharomyces cerevisiae'' or ''S. pastorianus'', Flanders Red Ales are fermented with a [[Mixed Fermentation|mixed culture fermentation]]. At one brewery (presumed to be Rodenbach) studied by Martens et al.(1997) and then later by Dusart et al. (2022), two beers were produced using mixed fermentation and blended together. The first "light beer" was 11°P and was less acidic, while the second "heavy beer" was 13°P and served aged unblended as an Old Ale. Both beers were inoculated with an acid washed yeast slurry that was harvested from a previous fermentation of the "light beer". The yeast slurry contained about 5% lactic acid bacteria after the acid wash. The fermentation of these beers had three stages<ref name="Martens">[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1997.tb00939.x/abstract MICROBIOLOGICAL ASPECTS OF A MIXED YEAST—BACTERIAL FERMENTATION IN THE PRODUCTION OF A SPECIAL BELGIAN ACIDIC ALE. H. Martens, D. Iserentant andH. Verachtert. 1997.]</ref><ref name="Dusart_2022" />: # A seven day ethanol fermentation at 21°C dominated by ''Saccharomyces''(also present was lactic acid bacteria which was kept to a minimal population due to the acid washing process). After this seven day fermentation, the yeast is harvested and washed for the next brew <ref name="Dusart_2022" />. # A four to five week lactic acid fermentation at 15–21 °C in epoxy-covered tanks dominated by ''Lactobacilli''<ref name="Dusart_2022" />. # The 11°P "light beer" is then blended with aged Old Ale and packaged (1/3 young "light beer" to 2/3 Old Ale), while the 13°P "heavy beer" is transferred to large wooden vats (foeders). # A The "heavy beer", which becomes Old Ale, is then aged for a twenty to twenty-four month period of time. During this time, the beer undergoes a long and slow fermentation that is dominated by ''Brettanomyces'', ''Lactobacilli'', ''Pediococcus'', and acetic acid bacteria (''Acetobacter''). Most of the aged Old Ale is blended with fresh "light beer", but a small amount is packaged unblended as "Rodenbach Vintage" <ref name="Dusart_2022" />.

The development of the third stage with ''Brettanomyces'' and ''Pediococcus'' was similar to the development of these microbes in [[Lambic]] fermentation. The "light beer" was never allowed to go through the third phase of fermentation, and was instead chilled to 0°C and then used to blend with previous batches of the "heavy beer" and then pasteurized during packaging for stability <ref name="Martens">[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1997.tb00939.x/abstract MICROBIOLOGICAL ASPECTS OF A MIXED YEAST—BACTERIAL FERMENTATION IN THE PRODUCTION OF A SPECIAL BELGIAN ACIDIC ALE. H. Martens, D. Iserentant andH. Verachtert. 1997.]</ref>.