Well, 100% pure means made only of one natural product, not adulterated, no preservatives and no carriers of any kind. Do you believed that instant coffee powders are made of nothing but coffee only? It is up to you to decide and do some deeper research.
Based on the mini magazine “The Ultimate Guide to Philippine Coffee”, the invention of instant coffee powder was triggered by the oversupply of Brazilian coffee in 1930s. It came to the point when some produce need to be destroyed to prevent its price drop. The help of coffee companies were asked to help expand its consumption and solve the oversupply problem.
The brand Nescafe was born after eight years of research and development. Instant coffee powder made of brewed Robusta coffee. No carriers and other ingredients were mentioned in the process.
Instant coffee has the advantage of easy preparation, easy and light transport and very long shelf life if contained in a good package. Has inferior in taste though.
There are other coffee brands that were developed earlier but not mentioned by the mag.
Green beans are roasted then extracted by percolation at temperature of 155 to 180°C. This contradicts the normal brewing process which only requires about 90°C. The high temperature extraction plus the additional heat of spray/free drying might have a great deal on flavor loss.