hi all, new to brewing, iv been using 2 litre pop bottles with my first brew attempt and seemed to work fine, though they got really hard and i was afraid they would burst!! they were fine, my question is, can i re use these old pop bottles or will they be weaker now they have been used once by companies for lilt and dr pepper and then by me once for beer!!! will they last again and again?? any advice will be helpful!!!