The following is an excerpt from Cook’s Science: How to Unlock Flavor in 50 of Our Favorite Ingredients, by the editors at America’s Test Kitchen.

Apples, which belong to the genus Malus, a member of the rose family botanically named Rosaceae, have been grown for thousands of years. DNA mapping has shown them to originate from the wild apple, Malus sieversii, in a region of Central Asia that includes southern Kazakhstan and Kyrgyzstan. And they are more complicated than you’d think: Apples have the largest genome of any known plant, containing 57,000 genes. (Even the human genome contains only about 30,000 genes.) Today there are around 6,000 cultivars of apples (though only a dozen or so in the average supermarket). China is the world’s largest producer, with the United States ranking number two.

Over the years, apples have been bred for one of three purposes: eating, cooking, or juice production. This means that varieties that are best for eating are not the best for cooking, and vice versa. It all comes down to the texture, which depends on a few things: the structure and composition of the cell walls, the amount of air between the apple cells, and the amount of acid in the apple. Storage conditions are also important.

First, the cell walls of apples are made of cellulose and hemicellulose, held together with pectin. Pectin is a complex polysaccharide that holds the cells of many fruits and vegetables together, as well as forms part of the cell wall structure, providing strength. Pectin is strengthened by calcium ions that link its molecules together. Apples that are best for cooking tend to have pectin reinforced with more calcium than apples that are best for eating. In addition, about 25 percent of the volume of an apple is composed of air held in open spaces between the cells. These air pockets expand with steam during cooking and can result in rupture, collapse, and release of juice, especially in eating apples. And, finally, acid strengthens pectin and keeps it from dissolving so readily when heated. Naturally acidic apples, such as Granny Smiths, are more likely to hold their shape than other varieties. This is why we like to use Granny Smiths for baking.

Cook’s Science: How to Unlock Flavor in 50 of Our Favorite Ingredients

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Apples are a climacteric fruit, meaning they continue to ripen following harvest. Like most climacteric fruit, they are harvested before becoming fully ripe. At this stage apples still contain a lot of tart, sour-tasting malic acid and starch, which means they tend to be more sour than sweet. A few important things take place during ripening: First, apples use some of the acid for energy and metabolism; second, they convert much of their starch to sugars; finally, an enzyme known as polygalacturonase gradually breaks down some of the pectin.

When it comes to cooking, we stick to only a few types of apples—apples that are readily available in the supermarket, all year round, and apples that are better equipped to deal with heat. This means apples with more calcium-reinforced pectin, more acid, and less space between their cells. First place? Granny Smith. Here, we use them to make a double-layered French Apple Cake, in which the Granny Smiths remain intact with the help of a little precooking. We lightly caramelize whole, hollowed-out Granny Smiths, which stand up to the oven in our Best Baked Apples. Finally, for our French Apple Tart, we use Golden Delicious apples, which break down more readily, in two ways—reduced into a puree as the base of the tart, and in slightly precooked, still-intact slices arranged in a rosette—for a dessert that’s simple and fancy at the same time.

Test Kitchen Experiment

In the test kitchen we turn to Granny Smith apples again and again for baking applications. Their high acidity provides great balance in sweet applications, but often it’s their firm texture (and ability to retain that firmness during cooking) that makes them our top pick. We were curious how some of the lesser-known, less-available, or newer apples measured up. We set up the following experiment.

Experiment

We gathered 10 apple varieties and measured their initial firmness using a CT3 Texture Analyzer. We then cooked slices of each apple at 185 degrees (a temperature at which pectin quickly breaks down) until they registered the same soft texture. We tracked how long each variety took to reach the same endpoint and compared that to the initial firmness to look for a potential correlation. For a more visual (and real-world) representation, we also baked each type of apple whole, on a baking sheet in a 350-degree oven until they softened. We used the data for Granny Smith apples as a benchmark for comparison.

Results

We found a clear correlation between the initial firmness of a particular apple and how long that sample took to soften. Specifically, the firmer the raw apple, the longer it took to soften. When we organized the results by apple variety, we noticed clear trends that can help dictate best uses for a given variety.  

Takeaway

Based on our tests we were able to group the apple varieties into a few categories. McIntosh, Red Delicious, and Golden Delicious soften rapidly and are better suited to applesauce or apple butter where the end goal is a completely soft texture. At the other end of the spectrum we found that Pink Lady, Braeburn, and Honeycrisp perform similarly to our perennial pie favorite, Granny Smith. These apples start out firm and retain their texture well during extended cooking. In the middle of the pack we grouped Gala, Jonagold, and Empire apples together. Many factors contribute to apple texture when both raw and cooked. Chief among them is the strength of the pectin, which provides structure in the cell walls of the apple. Apples that are higher in calcium and acidity, which both reinforce pectin, generally hold up better to cooking. (Tart apples also tend to be firmer than sweet apples.)

Beyond texture, each type of apple varies in sweetness and acidity so that should be a consideration when choosing an apple for a particular application. While apple varieties performed relatively consistently from test to test, there were exceptions among individual apples within a variety. The bottom line? If you start with a mealy, soft apple it will turn to mush quickly, no matter the variety.

Excerpt from Cook’s Science: How to Unlock Flavor in 50 of Our Favorite Ingredients, by the Editors at America’s Test Kitchen. Text copyright © 2016 by the Editors at America’s Test Kitchen. Reprinted by permission of America’s Test Kitchen.