As summer heats up, there are lots of great ways to cool down, but there’s nothing cooler than lemonade. Get just the right blend of sweet and tart; then sit back and chill.

“Lemonade is a comfort drink as opposed to comfort food,” said Fred Thompson, author of “Lemonade: 50 Cool Recipes for Classic, Flavored and Hard Lemonades and Sparklers” (Harvard Common Press, $10.95).

Raspberry lemonade is one variation of the popular summer cooler. See this recipe and others on page 2D.

The secret to lemonade is the balancing act between its three essential ingredients: lemons, water and sugar.

“It should be sweet at the beginning, and tart as it leaves the mouth,” Thompson said. “Compared to wine, which might be a bit of a stretch, the tartness can be compared to the tannins in red wine.”

Lemonade is a year-round drink, but nothing beats its sweet, tart and oh-so-cool refreshment on a hot summer day.

While some insist that lemonade is best made with a simple syrup sugar dissolved in boiling water Thompson said it works just fine to stir the sugar into the water until it melts. Then add the lemon juice.

“Simple syrup is an easy way to do it, though, and it makes it easy to adjust the sweetness,” he said. “Everyone has their own flavor profile.”

The 50 recipes in Thompson’s book range from simple and traditional to sophisticated drinks with new twists such as herb-infused, sparkling or spiked versions of lemonade.

“Lemonade blends really well with summer fruits strawberries, blueberries, watermelon, peaches, about anything you want to mix it with,” he said.

He even includes a ginger lemonade and a thyme-infused version.

Still not convinced that making lemonade from scratch is worth the effort?

“There’s a big, big difference,” Thompson said. “But sometimes you have to punt.”

If that’s the case, use store-bought refrigerated lemonade or frozen concentrate. Do not use powdered mixes, which Thompson calls “belly wash,” and under no circumstances should you use reconstituted lemon juice.

“I’d go to belly wash before reconstituted lemon juice,” he said. “It’s very acidic. It has a bitter taste.”

In his book, Thompson says that frozen lemonade concentrates work just fine in flavored lemonades. They provide quick, intense flavor.

He also includes tips for improving the flavor of mixes or concentrates by adding small amounts of fresh lemon juice, lemon rind and sugar.

But since from-scratch lemonade is so simple to prepare and the flavor is much superior to commercial versions, Thompson says you should never have to ask the question: “To squeeze or not to squeeze?”