White wool fabric can take on a yellow tinge over time. Age is the most common cause, but improper care hastens the process and makes the yellow discoloration more intense. Exposure to sunlight and storing white wool clothing, bedding or linens in an airtight space can also cause yellowing. Harsh cleaning products cause yellow stains on white wool. You can remove yellow discolorations caused by age and damage from wool fabrics with a simple, gentle cleaning process.
Combine 2 tablespoons of white vinegar with 2 cups of water, and pour it into a spray bottle. It's best to use distilled or filtered water, which have no minerals or chemicals to discolor the wool.
Lay your wool piece out flat -- surfaces such as the sink counter or tub work well. Lay the fabric or garment out as flat as possible.
Use the spray bottle to saturate the yellowed areas with the vinegar and water solution. Completely saturate the fabric, and go past the edges of the yellow discolorations.
Allow the solution to remain on the fabric for 10 minutes, and then wash either by hand or on the gentle cycle in cool water. Hang, or lay flat to dry.
Once the fabric is dry, inspect the discolorations, and repeat the process if necessary. It may take several tries to completely remove the discolorations.