Final answer:
Salsa fresca gets its spiciness from the capsaicin found in chilies like jalapeños, serranos, or habaneros. The seeds and membranes of these peppers contain higher concentrations of capsaicin, which can be adjusted for desired heat levels.
Step-by-step explanation:
The spicy taste in salsa fresca is primarily due to the presence of capsaicin in chilies that are used as one of the ingredients. Capsaicin is a chemical compound that stimulates the heat receptors in the mouth, creating a spicy sensation. Salsa fresca may contain a variety of chilies such as jalapeños, serranos, or habaneros, each contributing varying levels of heat. Additionally, the seeds and membranes of the peppers contain higher concentrations of capsaicin, and including them in the salsa can increase its spiciness. The level of spiciness in salsa fresca can be adjusted according to personal preference by varying the type and amount of chilies used.