Does Racking to a secondary slow or stop fermentation

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If yeast are still alive and active in your beer, moving them into a second container isn't going to stop them. Racking beer off the yeast cake could slow things down a bit, but it won't stop it.

The better question is: Why would you rack to secondary before fermentation is done? The whole point is that your primary carboy ferments the beer, your secondary (if you choose to use one, many don't) is for after fermentation is complete to allow the beer to clean and clear up.
Generally speaking, yes, it can stall or severely slow fermentation. If the krausen has just dropped, and you rack to secondary, you probably will not drop another point. I made this mistake on my first batch. I racked after 4 days and it ended up sweet (FG 1.020). That is stupidly high for Nottingham.
Using a secondary can be misleading when it comes to fermentation activity. In a secondary you can actually observe what is going on. In a primary such as a plastic bucket, you have no indication of fermentation progress beyond the airlock or overflow.

Using a primary (plastic bucket) and transfering after a week or two, I have noticed the airlock bubbling well, when no activity was seen prior to racking.
This included additional krausen production. In the process of racking, you do aerate the beer and thereby provide additional O2 for the yeast to continue their work consuming whatever is still available. This is of course if you are simply racking to a carboy which has not been purged with CO2 or you use a vacuum pump to keep O2 from being introduced.

Just my observations and my $0.02 worth. I am by no means an expert on the matter.

Salute! :mug: