Learn Spanish (Latin America): El jugo está agrio.

In Spanish, we use estar (here as está) to talk about how food or drink tastes right now, or its current condition. Using está implies that this specific juice tastes sour at this moment. If you used es, it would mean being sour is a permanent, defining characteristic of all juice.

Does agrio change if we are talking about a feminine noun?

Yes! Adjectives must match the gender of the noun they describe. Because el jugo is masculine, we use agrio. If we were talking about a feminine noun, like a grapefruit (la toronja), we would change the ending and say la toronja está agria.

I have seen the word zumo for juice. Is jugo different?

They mean the exact same thing, but jugo is the standard word for juice in Latin America. Zumo is primarily used in Spain.

Why is there an accent mark on está?

The accent mark shows that the spoken stress falls on the last syllable. It also importantly separates it from esta (without an accent), which means 'this' as in esta bebida (this drink).