[ Equipment: digital convection oven, cookie sheet, 8-1/2 x 4-1/2 x 2-1/2 (inch) loaf pan, 8 inch square cake pan. For more information about the terminology in this recipe, see Low Temperature Baking: A Journey of 3 Paths ].
Until now, all the slow-baked pastries I've made have been 7 inches or less in diameter, the maximum size that will fit in my temperature-controlled slow-cooker oven. When I resolved to try making them in standard size pans (8 inch or larger rounds and squares), I ordered a digital convection toaster oven (a Cuisinart CTO-395 with Exact Heat sensor) for these bigger jobs. The CTO-395's 0.6cu capacity sits somewhere between a regular toaster oven and a full-size counter-top oven.
The circulating heat and top/bottom heating elements not only bake food faster but also more consistently, even at 250°F/121°C. General LTB recipe guidelines still apply, however, and the convection feature does reduce baking time. The CTO-395 dehydrates foods very quickly too. With a second baking rack, I'd be able to dry two trays of food at once. Cuisinart sells extra racks for $14 each.
The digital thermostat keeps the temperature fairly stable (no more fidgeting with the heat dial), but I continue to monitor it with a thermometer. Since this toaster oven consumes around 1800 watts, it's not even close to matching a slow cooker for energy efficiency. For large scale LTB baking (entertaining) and recipe testing, it's my appliance of choice. Prices for digital counter-top ovens have fallen drastically. many going for less than $100 US. I've seen the Cuisinart CTO-395 on sale for less than the price of a high-end plain bread toaster.
Below are the results of some of my tests baking and dehydrating with the convection oven. With the exception of the banana chips, the tests were run with prepared mixes and doughs from my local market, so I could get some idea of how well convection ovens bake at low temperature. All required some modification to the instructions or to the mix for good turnouts.
First up is Jiffy Blueberry Muffin Mix, which I made into a cake in an 8-inch square pan, following instructions on the box.
The picture above shows slices from two Jiffy cakes, one baked at 375°F/190°C on the left and the other at 250°F/121°C. The high temperature one rose higher and fluffier, but was dry, virtually tasteless, almost like eating cotton. The Jiffy mix contains artificial blueberries, which apparently lose their aroma and flavor when baked at high temperature. The 250°F cake retained the blueberry flavor, had a moist, dense texture, and I could also taste the eggs.
To boost the LTB cake's height, I added 1/2 teaspoon of baking powder to the mix. That cake rose higher in the oven, but collapsed, because the center didn't heat up fast enough. In the picture above, I covered the pan with aluminum foil and cut out a 4-inch hole so that the batter in the center would bake faster.
This picture compares two Jiffy cakes baked at 250°F/121°C for 35 minutes (about 60% more time than at 375°F/190°C). The top one is the plain mix, baked in an uncovered pan. The second one contains the extra baking powder and was baked in the foil-covered pan as described in the preceding paragraph. It rose to the same height as the high temperature cake with similar browning on the edges.
The texture of the second cake is as fluffy as the high temperature but with stronger blueberry and egg flavor.
Next trial was Nestle Toll House prepared cookie dough. Out of the package, the dough is scored into 12 chunks for 12 "big" cookies.
The instructions said to break off pieces of the dough and place them on the baking sheet. To help the cookies bake faster, I flattened the chunks into 2-inch disks.
The recommended oven temperature was 325°F/163°C for about 10-15 minutes. I baked them at 250°F/121°C for about 15-20 minutes until the edges were a light golden color.
In the pictures, I only made a batch of 3 cookies, but the baking sheet (a 10-inch sheet from Wilton) could accommodate 4 of them, and up to 6 cookies with careful placement. Each chunk of dough spread out into a 3-1/4 inch cookie. LTB Toll House cookies fresh from the oven: such intense chocolate, milk and molasses flavors that one cookie satisfies like a whole box of the regular kind.
The oven can fit a 8.5 x 4.5 x 2.5 inch loaf pan, so I made a chocolate banana loaf cake from a Betty Crocker chocolate cake (devil's food) mix. For the one in these pictures, I measured out half of the mix by weight (approximately 9.5 oz). Then I added 1 egg, 1 teaspoon baking powder, 1/3 cup mashed banana and about 1/2 cup water. The batter was a little thicker than as prepared by the box instructions. The baking powder helped boost the rise, and the reduction in overall hydration balanced texture vs. baking time.
Because the center of a loaf cake heats up slowly, I covered the pan with foil and cut out a hole leaving about a 1-inch foil border around the edge. The foil border is meant to mediate over-baking at the edges of the cake, while exposing the center to maximum heat and vapor dispersion.
Baked at 250°F/121°C for about 1 hour, the cake more than doubled in height. In the future, I might try 1/2 teaspoon of baking powder instead, because the center sank a little, which sometimes happens when there is too much leavening.
Although it it contains just 1/3 cup of mashed banana pulp, the banana flavor really stands out in the moist chocolate cake.
Because convection ovens circulate hot air with a fan, I expected them to be very effective food dehydrators. For the the last test, I made banana chips on the 2-piece broiling pan that came with the oven. Perforations in the top section of the pan let air circulate around the food, and the bottom section (drip pan) holds the top up to avoid scorching from the heating elements.
So that the banana chips don't stick to the pan, I greased the perforated section with vegetable oil. I laid out 1/4-inch thick slices on the pan, positioning every slice over 1 or more holes. I didn't treat the slices with any preservative. They turned brown a little as they dried.
The lowest settable temperature in my Cuisinart oven is 150°F/65°C, too high for drying fruits and vegetables without damaging beneficial enzymes. I propped the oven door open with a crumpled piece of foil, just enough to keep the temperature steady around 110-120°F/43-49°C.
About 5 hours later, the slices had deflated into chips. They were still soft. I peeled them off the pan, loosening them by sliding the blade of a plastic knife underneath, and dropped them into bowl lined with a paper towel. A few more hours of air-drying hardened the chips.
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