Remove the outer shell, stems and strings from the tamarind pods. Place tamarind pods in a small, non-reactive saucepan with water, bring to a boil. Allow to boil for two minutes, remove from the heat and allow to cool completely. Using the back of a spoon to release as much of the tamarind pulp as possible. Strain through a fine mesh sieve into the blender. Add sugar and lemon juice, blend until smooth. Place in fridge to chill until ready to serve. To make shandy pour ¼ cup tamarind lemonade into chilled glass and top with chilled Montejo cerveza.