▁vol atile ▁fat ty ▁ac ids ▁( VF As ), ▁such ▁as ▁ac etic , ▁prop ionic , ▁la ctic , ▁and ▁but y ric ▁ac ids . ▁By ▁lower ing ▁p H , ▁these ▁create ▁a ▁host ile ▁environment ▁for ▁compet ing ▁b acter ia ▁that ▁might ▁cause ▁spo il age . ▁The ▁V F As ▁thus ▁act ▁as ▁natural ▁pres erv atives , ▁in ▁the ▁same ▁way ▁that ▁the ▁la ctic ▁acid ▁in ▁y og urt ▁and ▁che ese ▁increases ▁the ▁pres erv ability ▁of ▁what ▁began ▁as ▁milk , ▁or ▁vin eg ar ▁( d il ute ▁ac etic ▁acid ) ▁pres erves ▁pick led ▁veget ables . ▁This ▁pres erv ative ▁action ▁is ▁particularly ▁important ▁during ▁winter ▁in ▁temper ate ▁regions , ▁when ▁green ▁for age ▁is ▁un available . ▁When ▁sil age ▁is ▁prepared ▁under ▁optimal ▁conditions , ▁the ▁mod est ▁acid ity ▁also ▁has ▁the ▁effect ▁of ▁impro ving ▁pal at ability ▁and ▁provides ▁a ▁di et ary ▁contrast ▁for ▁the ▁animal . ▁( However , ▁excess ive ▁production ▁of ▁ac etic ▁and ▁but y ric ▁ac ids ▁can ▁reduce ▁pal at ability : ▁the ▁mix ▁of ▁b acter ia ▁is ▁ide ally ▁chosen ▁so ▁as ▁to ▁maxim ize ▁la ctic ▁acid ▁production .) ▁Several ▁of ▁the ▁fer ment ing ▁organ isms ▁produce ▁vit am ins : ▁for ▁example , ▁la ct ob ac ill us ▁species ▁produce ▁fol ic ▁acid ▁and ▁vit amin ▁B 1 2 . ▁The ▁fer ment ation ▁process ▁that ▁produces ▁V FA