Hi everyone 
How long can I use a top cropping yeast? In “Yeast” by Chris White there’s written (about a top or bottom cropping yeast): “After four weeks, the yeast viability is usually 50 percent or less. Ideally, you do not want to pitch yeast that has dropped below 90 percent viability.”
But in other web sites there’s il written that top cropping yeast loses 20% of his vitality every month, and so I can use a top cropping yeast until 5 or 6 month.
What’s your experience?
Thanks 