Changes

"Mushrooming" is the actual or perception of the compression of the top part of the cork that protrudes out of the bottle, and is often preferred for the aesthetics. The practical benefits of mushrooming are debatable. Some people believe that this compression is due to high carbonation in the bottle pushing the cork out of the bottle, which is held in by the cage. However, in many cases the cork may not actually be compresseddue to carbonation, but just appears to be compressed by the cage due to the much thinner "leg" of the cork which is compressed by the lip of the bottle (see [http://www.notcot.com/images/2009/09/gatinoismain.jpg this image] for an example). A more likely explanation is that the lip of the bottle compresses the "leg" of the cork, making the top portion look like a mushroom, but this top portion of the cork may not actually be compressed at all. Some people claim that manual mushrooming makes removing the cork easierand allowing for more "pop" noise, while others say that mushrooming does not serve any functional purpose and is not necessary. See [https://www.facebook.com/groups/MilkTheFunk/permalink/1920123874682484/ this MTF thread] for more informationopinions from various brewers.

This Actual mushrooming of the cork can be accomplished manually by hand, though be aware that flaws in the bottle may cause the neck to break, which would be a very dangerous situation if you are applying the downward force by your hand. It can more easily and safely be applied with a bench capper. Put the cage on the cork and compress both with a bench capper. Hold the bench capper arm in place with your shoulder/armpit, leaving both hands free to orient and twist the cage. Special cage twisting tools are available, though pens such as sharpies or some interchangeable screwdrivers are about the right size. You could also use twist lock pliers if you have them around.