a drier and cooler starter has less bacterial activity and more yeast growth, which results in the bacterial production of more acetic acid relative to lactic acid. conversely, a wetter and warmer starter has more bacterial activity and less yeast growth, with more lactic acid relative to acetic acid. the yeasts produce mainly co2 and ethanol. high amounts of lactic acid are desired in rye and mixed-rye fermentations, while relatively higher amounts of acetic acid are desired in wheat fermentations. a dry, cool starter produces a sourer loaf than a wet, warm one. firm starters (such as the flemish desem starter, which may be buried in a large container of flour to prevent drying out) tend to be more resource-intensive than wet ones.