Making beer with grain generates trub and hop debris etc. That has all been dealt with in kit brewing, before the kit is packaged and sent out to the shops. We deal with that by filtering as well as possible, and paint strainers are a good method, I might even try one myself. And by being patient, and allowing nature and gravity to have their say, by completing the fermentation process and dropping out all the solids, so we can rack the beer off it all and package clear beer.
It is common practice in the USA to rack from the primary after the main fermentation has died down to get the beer off the dead yeast and trub, and allow fermentation to continue its last quiet phase and then settle and condition before packaging. They generally use glass for the second phase. And they tend to dry hop in the second FV. But I have found that leaving the beer in the primary for three weeks allows all this to take place with no apparent ill effects. I may give it another go though, the yanks claim that leaving the beer on the dead yeast is not good, as the live yeast can start to devour the dead yeast and produce off flavours. I did a secondary using a steel stockpot once, and the beer was very very good. 16 days primary, 11 days secondary. Hmm....
John Palmer says, though, in the old online version of How to Brew:
"There has been a lot of controversy within the homebrewing community on the value of racking beers, particularly ales, to secondary fermentors. Many seasoned homebrewers have declared that there is no real taste benefit and that the dangers of contamination and the cost in additional time are not worth what little benefit there may be. While I will agree that for a new brewer's first, low gravity, pale beer that the risks probably outweigh the benefits; I have always argued that through careful transfer, secondary fermentation is beneficial to nearly all beer styles. But for now, I will advise new brewers to only use a single fermentor until they have gained some experience with racking and sanitation.
Leaving an ale beer in the primary fermentor for a total of 2-3 weeks (instead of just the one week most canned kits recommend), will provide time for the conditioning reactions and improve the beer. This extra time will also let more sediment settle out before bottling, resulting in a clearer beer and easier pouring. And, three weeks in the primary fermentor is usually not enough time for off-flavors to occur."
Which has caused me to generally do 3 weeks primary fermentation and then bottle, for most of my brewing career. I actually think the difference is likely to be negligible, and it's mostly about avoiding infection and oxidation and allowing enough time for the beer to ferment out fully and clear before you bottle or keg.
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