I am interested in the caffeine content in various coffees.
Will day-old coffee have much less caffeine? I am refering to espresso drinks such as the Starbucks Americano or the drip coffees also available there. Does refrigeration make much difference to the half-life? What about re-heating?
How about instant? I have seen charts comparing caffeine content in various fresh coffees but not instant. What is the typical caffeine content of instant coffee? What is the half-life of caffeine in instant coffee on the shelf as a room temperature solid?