I have some old bacon that has developed alkaline tasting crystals. Is it safe? It's been kept in the fridge, and it's perhaps 2 or 3 weeks old.
Still Tasty recommends no more than one week refrigerated for what is in the US is called Canadian bacon, and may be called back bacon elsewhere, if that is the product you are referring to.
Similarly, they recommend no more than 8-10 days refrigerated for an open package of what in the US is simply called bacon, but elsewhere may be known as streaky bacon.
In either case, depending on what you are referring to, I would consider the product suspect, and suggest you discard it. I cannot conceive of any circumstance in which an alkaline taste in a meat product is a good thing.
The bottom line, however is what ElendilTheTall said: when in doubt, throw it out. Use your good judgement. He really did answer the heart of your question.