Brettanomyces will make your beer taste phenolic. Lactic Acid Bacteria will sour it (Lactobacillus and Pediococcus are two common contaminants).
Oxygenation will gradually make the beer taste like cardboard.
Hop aromatics degrade rapidly, heavily hopped beers are best within a month of brewing.
Very few beers get better over time (generally sours and stouts), most are beginning to degrade immediately and fall off a cliff within a year.
Also as you probably already know brett, lacto and pedio are desirable sometimes.
Brettanomyces will make your beer taste phenolic. Lactic Acid Bacteria will sour it (Lactobacillus and Pediococcus are two common contaminants).
Oxygenation will gradually make the beer taste like cardboard.
Hop aromatics degrade rapidly, heavily hopped beers are best within a month of brewing.
Very few beers get better over time (generally sours and stouts), most are beginning to degrade immediately and fall off a cliff within a year.