Possible Clues:

• The reason behind why one has to limit the amount of beer
• Reasons to keep drink under control
• The logical basis of some thing or action
• The theory behind this is to allow only so much beer, it seems
• Allowed only so much beer, perhaps, and with reason
• Helping porter within reason
• The reasoning behind this is only to allow so much beer
• Limit the consumption of beer?
• That's the reason for the 10 across of a northern beer
• Reasoned exposition