Look at the fresh color of lemon. It's very bright, bright yellow, and the color will be very uniform. It won't be yellow and green. The skin is bright. The knot on the top is green, which is the place originally connected with the tree. After picking it, it usually leaves a small green top, just like the thing like a knot on the top of an orange, If it's brown, it means the lemon is not fresh. 2. Try to feel stronger, harder is more acid, and softer will not be so acid, but do not buy soft, soft is not fresh. 3. The overall round shape is less sour, but more juice; The sharper will be more sour, but the juice will be less.