Nuts may seem like an ingredient you can just throw in the pantry without fear of spoilage, but using old pecans leaves your pie with a sour note. The high fat content in the nuts is responsible for their buttery taste, but it also makes them prone to going bad quickly. If stored incorrectly, the pecans may experience oxidation quickly, leading to a rancid taste. To elevate your homemade pecan pie, keep the nuts in a cool, dark place, like the fridge. For a longer lifespan, opt for shelled pecans - the covering protects the nuts from oxygen and moisture.