What is the recommended shelf life for a keg once tapped at a bar? Assuming it's not a whale but a standard beer, couple of weeks, longer? I don't have much knowledge on that aspect so any info would be great!
Forty days is what sticks out in my mind from what brewers have told me. Ideally, a bar with fewer than twenty tap lines should take less than two weeks to sell-through a keg, but yeah, Micromatic gives the 45 to 60 days estimate: http://www.micromatic.com/beer-questions/how-long-keg-beer-remain-fresh-aid-44.html
Does this vary by style? I'd think with it being under pressure and being cold it would keep longer. Have been tossing around the idea of a kegerator (I'm sure we all have) but don't think we'd finish anything in a month.
I've had something in the kegerator before for near 3 months and didn't notice any drop off. If it's that long it's a half keg of something like Sierra Nevada Pale Ale and it's just fine for that long. Typically I get sixtels though and they're usually gone within a month so it's never been a problem for me. Just like some people won't drink an IPA that's more than ___ days old I'm sure some would say a 3 months is too long but I didn't notice any difference in the couple beers that I've had hang around that long.
I've got a neighbor that keeps a locally brewed blond ale tapped in his kegerator for up to a few months at a time. It's cold and on CO2 the whole time. It is still fine up to 90 days after being tapped. I don't think the same would hold true for a hop forward brew.
My concern wouldn't necessarily be for the beer in the keg but in the lines. If something is plugged in and moving so slowly, there is some gross beer in those lines, unless they are keeping up with maintenance (my assumption would be a place that can't move a keg in two months isn't). This is why I'll take a well curated 10-20 line beer program over "House of 1,000 Brews!" type quantity over quality places any time. The exception to the rule is Max's Taphouse in Baltimore. They manage to keep 100+ lines in excellent condition.
I'd say about 6 weeks. We have been open for 3 years and only had about 3 kegs go bad. We have a brewery now and have fewer taps than we used to, but used to carry 23 taps. We go through practically all of our beers in one to three weeks, but once in awhile you'll get a dog that won't sell. It'll get oxidized or DMS tasting by about six weeks. As an owner you can manage kegs going bad by getting slims of the slower selling stuff, and you eventually get a good feel as to what will and won't sell in your particular demographic region. There are factors that will slightly lengthen or shorten the shelf life a little like style, abv, and brewer's level of sophistication, but once tapped you can't do much about oxygen seeping in to the point that it eventually harms the beer.
