In response to Tiffany's experience with cold brewing I have two methods to try that I have found will resolve the problem of bitter tea.
The first is the most environmentally, and economically, friendly just reuse leaves that you have already enjoyed in a hot infusion earlier in the day.
Toss the used leaves into a glass pitcher, add water and let it sit. I prefer using an oolong or black tea for the most pronounced flavor with this method.
Time is less important than if you are using dry leaf so 4 hours, overnight, a couple days whenever you get back to it the tea will be perfect. Note the viscosity, or mouth feel, of the liquor when cold brewing like this. It makes for a nice cup and there is literally no waste. Re-infuse 2-3 times depending on your personal taste or strength preference.
The other way to avoid a bitter cup is to wash the leaf before you cold brew. In essence you are doing the same thing as above just not enjoying that first hot cup. Instead steep the leaves for up to 10 min., let them cool and continue as illustrated above.
My preferred method is the first one. I just leave the cold brewed leaves in the pitcher for weeks and every time I pour myself a glass or two I replenish the water in the pitcher and start all over again. At that point I start to add about 1/8 dry leaf to whatever is in the pitcher already. Then once again I let it sit. Unfortunately Astringency can be more pronounced in some teas, so my suggestion here is more of a guideline than a hard and fast “rule.” They way I was taught in Taiwan is not to use a tremendous amount of leaf, believe it or not the tea still delivers a nice character.
Tiffany, thanks for the question, and good luck.