Mile-High Lemon Meringue Tarts

From Women's Day, February 1, 2001, page 124 as posted by Dr. Patti Christie on: http://ocw.mit.edu/courses/special-programs/sp-287-kitchen-chemistry-spring-2009/readings/MITSP_287s09_read07_meringue.pdf

Ingredients:

Lemon filling

• 2/3 cup white sugar
• 2 tbps cornstarch
• 2/3 cup water
• yolks from 2 large eggs (reserve whites for meringue)
• 1/3 cup fresh lemon juice (from 1-2 lemons)
• 1 tbsp grated lemon peel (from 1 lemon)
• 1 tbsp butter
• 1 pkg (4 oz) ready-to-serve graham cracker crusts (6/pkg)

Meringue

• Egg whites from 4 large eggs
• 1/2 tsp Cider vinegar
• 1/2 tsp vanilla extract
• 1/2 cup sugar

Method:

Lemon filling

1. Whisk sugar and cornstarch in the top bowl of a double boiler to mix.
2. Whisk in water, egg yolks and lemon juice until smooth.
3. Place bowl over double boiler, stirring often with the whisk.
4. Boil, stirring constantly, 1 minute or until filling is translucent and thick.
5. Remove from heat. Add lemon peel and butter; stir until butter melts.
6. Pour 1/2 cup into each cracker crust and place on a rimmed baking sheet

Meringue

1. Heat oven to 350 degrees F.
2. Beat egg whites, vinegar and vanilla in a medium metal or copper bowl with a whisk until soft peaks form when whisk is lifted.
3. Gradually beat in sugar, 1 tbsp. at a time, increasing whisking speed and beating well after each addition until sugar dissolves.
4. Beat 2 minutes longer or until stiff peaks form when beaters are lifted.
5. Mound Meringue high on each tart, spread to edge of crust , then swirl with back of a teaspoon.
6. Bake 20 minutes or until meringue is browned an instant-read thermometer inserted in center of meringue registers 160 degrees F.
7. Cool completely on a wire rack, then refrigerate at least 2 hours or up to 8.
8. If you wish to share one, use a small sharp knife dipped in cold water to cut through the meringue smoothly.

Troubleshooting meringues

Meringues have a reputation for being troublesome. Keep in mind the following things:

• Under- or overbeaten foams leak syrup into unsightly beads and puddles.
• Undissolved sugar is undercooked syrup that has come to room temperature. If the sugar has not been completely dissolved, residual crystals attract water and create pockets of concentrated syrup (beads).  These meringues have a gritty texture.
• Too high an oven temperature squeezes wter from the coagulating proteins faster than it evaporates, producing syrup beads. It can also cause the foam to rise and crack, and turn its surface yellow.
• Weeping of syrup is caused by either undercooking a foam bottom in a hot oven and cold base, or overcooking the foam bottom in a moderate oven and hot base. To prevent weeping, cover the pie base with a layer of crumbs before adding the meringue topping and include starch or gelatin in the foam to help it retain moisture.
• Humidity is bad for meringues. Their sugary surface absorbs moisture from the air and gets sticky. Transfer dried meringues directly from the oven to an airtight container and serve immediately after removing from container.

Meringues

A meringue is a sweetened egg foam that generally stands on its own. Meringues obtain their stiffness and stability from sugar and heat. They are often baked slowly at low oven temperatures of 200 degrees F/93 degrees C. When browned in a hot oven or under a broiler, the surface gets crisp while the interior remains moist.

Meringues have a lot of sugar. The proportion of sugar to egg white ranges from 1:1 to 2:1. The higher, a 67% sugar content, is typical of jams. At this concentration, sugar reaches its water solubility at room temperature. Granulated sugar does not dissolve completely in a hard meringue. It leaves a gritty texture and weeping syrup drops. Confectioner's sugar or premade syrup are better suited for meringue use.

There are two main categories of meringues: uncooked and cooked.

Uncooked meringues are the simplest and most common. They vary in purpose and firmness based on the timing of the cook's addition of sugar. The lightest meringues are obtained by folding in the sugar only after the foam is formed. The sugar dissolves into the bubble walls and adds bulk and cohesiveness. These meringues are suitable for a spread pie topping or folding into a mousse or chiffon mix. If the sugar is beaten into the foam as it forms, it noticeably tightens the foam texture. These meringues get stiffer and can be shaped. Some cooks reverse the technique by beating the eggs gradually into the sugar. This process takes longer but a cook can form a foam in autopilot as it demans little attention. The resulting meringues are denser and less brittle. Therefore, the earlier the sugar is added, the firmer and finer the meringue.

Cooked meringues are more complex and are generally more dense. Heat incorporates the sugar better in the meringue and stabilizes the protein network into a solid structure. There are two basic cooked meringues:

• The Italian meringue is a syrup-cooked meringue. Sugar is made into a syrup first by heating sugar and water to 240 degrees F/115 degrees C. The whites are whipped to stiff peaks and then the syrup is streamed into the foam and beaten. The result is a fluffy, fine-textured, stiff foam. It can be used to decorate pastries or blend into batters and creams. Note: The heat from the hot syrup is not enough to kill salmonella as much of its heat gets lost to the bowl, whisk, and air.
• The Swiss meringue (similar to the French meringue cuite) is prepared by heating eggs, acid, and sugar in a hot bath and then beaten into a stiff foam. This preparation pausterizes the egg whites before forming the foam. This meringue can be refrigerated for several days and is usually pipped into decorative shapes.