Tannin, the same substance that makes wine stains such a chore to clean up, can also pose problems for concrete outside. Concrete is a porous material and, due to that fact, can easily become discolored from natural environmental factors. Tannin from surrounding acorns and trees can cause brown stains on concrete. If you only employ soap and water, you won't have a great deal of success removing the stains. A few special ingredients can make the task far easier and you don't even need to be exact in your measurements
Place a few teaspoons each of tea tree oil and glycerin in a bucket.
Add a few quarts of hot water to the bucket.
Brush the solution on your stains. Allow to sit for 20 to 30 minutes.
Scrub the stains again.
Rinse with fresh water.