We've had Sake chilling in our fridge for about a year now. It has been opened. Is this still safe to drink or is it time to throw it out?
Unless contaminated by, say, drinking straight out of the bottle, it will likely be safe to consume, but it will probably have deteriorated in quality.
Sake which is no longer appealing to drink may be suitable for use in cooking; if you're not accustomed to cooking with sake, consider something simple, like potatoes simmered with a modest amount of water, sake, salt & pepper, soy sauce and butter.
Low-alcohol beverages, whether fermented or slightly fortified, tend to deteriorate in quality over time, although they will become stale less slowly if their containers are sealed airtight and chilled. Port, marsala, sherry, vermouth, wine and sake all typically best consumed within a short time after opening, although the specific chemistry may vary.
Some folks consider a sake that's been open, unrefrigerated, for more than a few weeks undrinkable. I don't know if I'm that rigid, but it's a good benchmark. I've seen certain sakes do ok for a few months in the refrigerator.
It will keep until it doesn't. Eventually it will spoil, but because sake is considerably above the magic number for alcohol concentration to be self preserving when sealed (>12.3% alcohol by volume), so long as you don't let any alcohol tolerant microbes into the bottle, then it will be fine.
Smell it first,'if it smells earthy, throw it out, if it smells vinegary, you can use it but it's not rally sake anymore, it's rice wine vinegar.
If you want, and if it's say half full, water it down and add a touch of cider vinegar to it. Cider vinegar isn't pasteurized so it will have live acetobacters in it and you can make your own vinegar. You need to cut the sake to half strength though otherwise it's too strong for the acetobacter to grow.