Frozen mugs have been quite popular for quite some time. They have also caused many quality issues at many establishments all across the country.
The main problem is the process of cleaning the glass. Wash, rinse and then disinfect. The issue is the glass is placed in the freezer prior to giving the dissenfectant a chance to dry. This is how it works - dry time. Now there is frozen disinfectant on the glass which never has a chance to do it's job of killing bugs.
The water rinse works well for reducing foam but may not rinse all of the disinfectant out of the glass. Now the beer may have an off taste.
As to the coldest beer in town. Be careful - you may be serving beer with more gas locked in the beer then you desire. You may be filling up your customers with gas to the point you may not be getting the additional sale. That first one may taste great due to being so cold, but then the belching begins!
Scott Zuhse, Instructor
Micro Matic Dispense Institute