Originally Posted by Coastarine

The way I see it, if I leave a beer in primary 3 weeks and someone else makes the same beer but puts it in the primary for 1 week and secondary for 2 weeks, there is no reason why his should be any clearer. I primary in a ported better bottle so I can rack carefully. So I guess "time spent" is the key.

Anything negatively buoyant in the beer will fall out given time. Doesn't matter if the yeast cake is there or not. If you get into extended periods of time, then I can see using a secondary.

Originally Posted by Texlaw

Oh, boy. Here comes this fun again. There are a few reasons why "secondary fermenter" is not a misnomer. For many brewers, some fermentation does occur in the secondary.

First, fermentation does not always complete in the primary. Racking beer to the secodnary rouses the yeast and often results in further attenuation. Getting those last few points out can be very important if you are bottling. Most bottle bombs are not the result of overpriming, in a sense, but of failing to reach full attentuation before priming. Even if you are kegging and want the clearest beer you can get, that little bit of fermentation in the secondary will help you along.

Second, some beer styles (or recipes) call for a second fermentation by adding more fermentables. In those cases, the brewer usually wants to rack off the old trub before adding those fermentables.

Finally, the practice of an extended primary fermentation, followed by immediate packaging, has only recently become common. Back before a homebrewer could reliably get excellent quality yeast, you wanted to get your beer off the inital trub as soon as possible or risk nasty consequences (e.g., autolysis). Often, that meant racking after fermentation had slowed but not completed, usually within the first several days after pitching. Fermentation clearly continued and completed in the secondary. Because many brewers who have been around for a good while don't like to fix things that ain't broke, they still follow that practice.

I still advise and use a secondary, even though I have high confidence in today's yeasts. I find [racking to a secondary] makes my brewing more consistant and, frankly, better. I also leave beer in the primary for at least 10 days after visible yeast activity begins, so that there is plenty of time for the yeast to both have its party and clean up, afterwards. I've tried a couple batches where I just leave the beer in the primary for three to four weeks and then kegging straight out, and I was slightly less happy with the results, both in the beer and in the perceived convenience (i.e., I did not see any extra convenience, as it was a greater hassle keeping trub out of the keg). On the other hand, I know many brewers who go straight from the primary to the package (or bottling bucket) with great results. Do what suits you.

Just as an aside, there is virtually no risk of introducing contamination when racking to the secondary, so long as you practice proper sanitation. You have a finished beer, there, still with quite a bit of yeast suspended within it. That is not a happy place for intruders to find refuge. You do, however, need to consider oxidation, but that also is not a problem with proper practice (e.g., avoid splashing, use a properly sized vessel). If you can purge your secondary with CO2, do that. If not, the CO2 that comes out of solution when you rack should provide plenty of protection.

As another aside, comparing homebrewing to industry brewing is a poor analogy, unless you have analgous equipment and practices. For those homebrewers with conical fermenters and who very quickly repitch slurry, the secondary might be a true bright tank. For the rest of us, not so much.