More important than its geological origin is the type of coffee being used. The two main types are Arabica and Robusta, with Robusta having TWICE the caffeine content as the higher quality Arabica.
From what I understand from the freeze dried process, used to create instant coffee, is that there is a loss of caffeine after processing. This is one of the reasons why the Robusta variety is used (the other reason being its a lot cheaper to use Robusta).
For a higher quality coffee experience, try buying fresh roasted 100% Arabica and grind and brew yourself. You will be amazed by the difference and likely never again drink instant coffee.
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