The Eureka variety is available year-round, while the Lisbon is generally available only during the winter months. Firm, heavier, bright yellow lemons are best and should be a little tender to the touch. While fresh lemons are very firm, extreme hardness indicates that the lemon is very old. Lemons with paler skin are more acidic; however, lemons with green patches also tend to be more acidic, too. A rough skin surface usually means less juice content. Smooth-skinned lemons tend to be juicier.