The strong button on the Keurig is to allow for you to brew a more stronger and more concentrated cup of coffee.
When you press the strong button on your Keurig brewer it adjusts the brewing process to use a higher coffee to water ratio.
The higher coffee to water ratio, results in a bolder taste and essentially makes the coffee stronger by using more coffee grounds for the same amount of water.
Pressing the strong button on the Keruig activates the setting that increases the coffee strength.
when the strong button is pressed on the Keurig it extends the brewing time slightly and allows for more extraction of flavor from the coffee grounds.
To use the strong button on your Keurig, you simply press the strong button on the Keurig before you select the brew size to make a stronger and bolder cup of coffee.
Strong coffee is made by using a lower coffee-to-water ratio (more grounds, less water) and refers to the concentration of the beverage rather than the roast level.
Espresso coffee drinks by definition, are a strong drink since it's brewed as a very concentrated form of coffee.