My lemon juice concentrate's use by date passed a few months ago. It was kept it in the fridge the whole time. Is it still safe to use it?
I also typically use bottled lemon juice, as my budget does not allow for fresh lemons.
Stilltasty says you should use the bottle within a week, but I've had success with keeping it much, much longer.
That said, this is one item that will not usually work well past its best-by date, I've found.
Maybe in the future, you could freeze it in cubes if you can't use it soon enough?
I just used lemon juice concentrate 1 1/2 years after the best-by date to cook with fish and it was fine. Citric acid is literally a preservative. Why not? What is supposed to preserve the preservatives?
With any food, when you are getting to months past the use by date, it would be wise to throw it out. Odds are that it is more an issue of the taste deteriorating, but why take any chances?
I wouldn't. I tend to be--at home, not at work!--of the "Eh, if it's not actually developing its own language, bung it in a pan and see what happens" school.
But months past the best-before is something even I won't mess with. Yes, best-before dates are incredibly conservative, and in many cases (e.g. honey) are irrelevant and used merely as a marketing technique. (Oh no, my X has expired, I need to buy more X.) But for one thing, flavour compounds in fruits (even pasteurised concentrates) break down over time, leaving a flat dull flavour. For another, it has almost certainly bounced around in temperature, possibly been contaminated by molds and yeasts living in your fridge (yes they do, and no it's not really something you need to worry about if there's turnover in your fridge and it's basically clean), and possible been cross-contaminated by other things. Sure, you're not going to dump raw meat in your bottle of lemon juice, but if you have been slightly careless (as we all are!) about putting the lid down on a contaminated cutting board...
Even if it is more acidic and concentrated... in the end it is a fruit juice, and fruit juices tend to spoil comparatively quick even in the fridge (very high water activity that anything that can deal with the acidity can take advantage of).