Is it ok to use 5-6yrs old yeast in cooking?

No, it's not advisable to use 5-6-year-old yeast in cooking. While yeast can have a long shelf life, over time, it can lose potency, accumulate bacteria, and produce off-flavors. This could compromise the quality and safety of your food. Yeast is a living microorganism, and its viability decreases with age, affecting its ability to ferment and leaven dough. To ensure optimal performance, it's recommended to use fresh or within the expiration date yeast for best results. Discard old yeast and purchase a fresh packet or jar before starting your baking or cooking project.