The shelf life of tea is really a big topic and it cannot simply be answered like green tea for one year, black much longer etc, since various varieties have their own properties, some do not store well, some do, even within the same category of tea. Even under a generic label such as Darjeeling. Some black tea are better aged than fresh, some aren’t.
You are absolutely correct that the storage condition affects tremendously too. The possibilities of modern technology also allow much better shelf life than in the past, but some markets are adapting quicker than others. I think this really should be a separate article in the Tea Guardian site to cover. I’ll see if we can push this into the long waiting list.
Meanwhile, pls refer to these articles where we discuss storage conditions and containers:
