"stuck" fermentation

CAUSES IN WORT
pH above 5.7
temperature too close to low end of yeast's fermentation range
inadequate aeration (empty bottle/stuck regulator)
insufficient nutrients (especially zinc)
contamination

CAUSES IN YEAST SLURRY
too warm storage conditions (over 34°F/1°C)
too long storage time (greater than 48 hours if unfed)
poor viability (less than 95%)
contamination

GUIDELINES
warm slurry to upper end of yeast's fermentation range
aerate if specific gravity has dropped less than 30% of expected total
add zinc to wort
add fresh, healthy yeast