From the passage provided, extract the low end in Celsius of the optimal coffee extraction temperature range.

Context: Coffee beans must be ground and brewed to create a beverage. The criteria for choosing a method include flavor and economy. Almost all methods of preparing coffee require that the beans be ground and then mixed with hot water long enough to allow the flavor to emerge but not so long as to draw out bitter compounds. The liquid can be consumed after the spent grounds are removed. Brewing considerations include the fineness of the grind, how the water is used to extract the flavor, the ratio of coffee grounds to water, additional flavorings such as sugar, milk, and spices, and the technique to be used to separate spent grounds. Optimal coffee extraction occurs between 91 and 96 °C. Ideal holding temperatures range from 85 to 88 °C to as high as 93 °C and the ideal serving temperature is 68 to 79 °C.

Answer: The low end of the optimal coffee extraction temperature range is 91 °C.