Make two litres at a time, steep on the counter for about eighteen hours, keep the concentrate in a jar in the fridge. Usually fine. This batch has gone boozy and slightly winey by day four, and there is a faint fizz on the tongue.
It has been warm in the kitchen. No mould or film that I can see. Is this the coffee fermenting, and is the fizzy part a reason to pour the lot away?
That is fermentation and the fizz settles it. Brewed coffee has dissolved sugars and other compounds that wild yeast and bacteria will happily work on given time and warmth, and you gave them both: eighteen hours on a warm counter and then four days in a jar.
Move the steep into the fridge. It takes a little longer and it is far less likely to go anywhere. Boozy, sour, fizzy or off, or anything with mould, film or cloudiness in it, pour away.
How long should concentrate actually last in the fridge? I have been assuming weeks.
A week or two is the usual guidance for concentrate, and the honest answer is make smaller batches rather than trying to find the edge. Two litres that you finish in five days never gets the chance to do this.
Worth checking the bag too. Some natural process coffees genuinely taste winey and it is on purpose.
To separate the two things in that last comment, because they are easy to confuse. An intentionally winey coffee tastes winey from the first cup and matches the tasting notes on the bag. A fermenting batch tasted normal on day one and has changed since, which is yours.
Filter properly as well. Fine sediment left in the concentrate gives the microbes more to work with, so get all the grounds out rather than most of them.
@gasket_was_filthy · last wk.
Check your kit before the next batch and be unreasonable about it. Coffee oils and residue in the jar, the mesh, the filter and especially the gaskets harbour microbes, and that carries stale and fermented flavours straight into the following brew.
Mine went off repeatedly until I took the silicone seal off the cold brew maker and found out what was living under it. Strip it down, hot water, every time.
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