White wool products, such as clothing or yarn, have a tendency to get yellow over time due to sunlight, moisture or natural oils in the fabric. While using bleach may seem like an obvious solution to this problem, it is not recommended. Bleach can weaken wool fabrics and can dissolve them. White vinegar, on the other hand, is a safe product you can use to restore yellowed wool back to its original white tone.
Pour two cups of water into a bucket. Add one tablespoon of white vinegar and mix the solution.
Saturate a sponge with the mixture and use it to blot your yellowed wool until it is completely covered with the solution. Work over a sink to avoid mess.
Hand wash your wool, or machine wash it according to its label.
Air dry your wool, then inspect it to make sure it is uniformly white. If you would like it to be whiter, repeat these steps.