Changes

''Megasphaera'' species produce large amounts of ''butyric acid'', as well as some acetic, isovaleric, valeric, and caproic acids. They are considered a true beer spoilage organism in beer. ''M. cerevisiae'' is a common species found in spoiled beer, and is a Gram-negative bacteria. They are obligate anaerobes, and die in the presence of oxygen. Growth occurs at a temperature range between 59°-98.6°F (15°-37°C), with an optimal growth rate at 82.4°F (28°C) <ref>[https://books.google.com/books?id=6JHxBwAAQBAJ&pg=PA238&lpg=PA238&dq=butyric+acid+bacteria+beer&source=bl&ots=knKFqJFgmA&sig=VmO6rhgzmwlqt_WXAlgm8I4Zgmg&hl=en&sa=X&ei=O8-FVcGQOYeggwTt9oPgAg&ved=0CDcQ6AEwAw#v=onepage&q=butyric%20acid%20bacteria%20beer&f=false Brewing Microbiology. Fergus Priest, Iain Campbell. Springer Science & Business Media, Jun 27, 2011.]</ref>. Growth of ''M. cerevisiae'' cannot occur above 5.3% abv, and slow slows significantly at 2.66% abv. Growth also stops at a pH of 4.0 <ref>[https://books.google.com/books?id=O0idBAAAQBAJ&pg=PA211&dq=Megasphaera+cerevisiae+ph&hl=en&sa=X&ei=CReGVf63PIunNt-Zo7gN&ved=0CB0Q6AEwAA#v=onepage&q=Megasphaera%20cerevisiae%20ph&f=false Brewing Microbiology: Managing Microbes, Ensuring Quality and Valorising Waste. Hill, Annie. Woodhead Publishing, May 26, 2015.]</ref>.