i think that you would find the amount of caffine in green tea quite negligible when you compare the small amount of leaves used to make your tea versus the content of coffee beans. I also am an avid green tea drinker - I have no other caffine other than the ‘useful’ caffine that comes from the tea leaves and I find that it does me no harm and actually benefits my practice by aiding the elimination process.
whilst the intention is always to be pure - sometimes we have to remember that while there may be many rounds on the reincarnation wheel according to some - we only get one shot at this life. And part of the process is to actually enjoy it.
Enjoy your tea - and your wine - if that is the worst that you do then I think your doing pretty well! 
