Digital Television -- Analog Tomatoes

Television channels converted to all digital transmission on June 12, 2009. In Puerto Rico the public reaction was similar to the coming of hurricanes: buy everything in your local electronic shop (even if it is not applicable to your problem). Even though the digital conversion had been announced for over 24 months, delayed since February, and published in every newspaper, the month of June entered with no converter boxes or antennas on the island.

Wanting to see the new world of digital television, the option was to go to Home Depot and build a quick Koch fractal antenna. It is amazing what you can do with 6 feet of 0.25" aluminum rod, an 11x14 sheet of Lexan, and some nuts. The Koch antenna is tuned to channel 26 (526 MHz), near the geometric mean of the channels available in San Juan

Bending and building the fractal

15 channels for ~$10

Analog Tomatoes

The harvest from Siembra Tres Vidas was composed of mainly beautiful tomatoes: beefsteak, Roma, and heirloom. Since eating 3 kg of tomatoes a week is a challenge, the goal was to create dried tomatoes that could be used in the place of sun dried.

In the analog world, tomatoes are dried on racks, mainly in Turkey, China, Brazil and the Central Valley of California. Drying tomatoes in the tropics is a little more difficult, mostly due to the high environmental humidity. Vegetables usually begin to mold before they dry.

A solution is hot air drying. However, high temperatures can affect color. Since we do not have a dehydrator in Puerto Rico, the next best option is a convection oven set to its lowest temperature, in our case 80C. Since large amounts of water can be trapped inside the tomato cell structure, salting the tomatoes can bring this water to the surface where it can be evaporated.

Start by rinsing the tomatoes and removing stems.

Beautiful mountain grown tomatoes

Cleaned and stemmed

Following washing, the tomatoes are sliced into eighths and spread on pizza racks of varying diameter. Salt was sprinkled on the cut tomatoes to extract water. It was assumed that the osmosis would continuously replenish the water lost to evaporation. The remaining salt would serve as seasoning and a preservative. Based on area, the tomatoes were salted to about 6mg salt per cm2.


Types of pizza racks used for drying; area exposed, and salt used.
Tray 1 will be a 'try rack' to test for weight loss during drying.

Tray	Diameter (cm)	Area (sq cm)	Salt (gm)	Screen Weight (gm)	Salt mg/cm2
1	19	283.53		52
2	30	706.86
3	35	962.11	6		6.24
4	40	1256.64	8		6.37
5	45	1590.43	10		6.29

Part of the recipe was to test how long and how quickly the tomatoes lost weight during drying. To test the weight loss (assumed to be water loss), a small pizza rack was designated a 'try plate'. This small 'try plate' could be removed at regular intervals and weighed. As discussed above, the try rack weighed 52 grams.

The small plate at right is the test rack

...and it weighs 342 grams at the start of drying

3.6 kg of tomatoes were cut, placed on racks, salted, then placed in the oven set to 80C convection baking. The oven door interlock was bypassed to allow hot air and water vapor to escape

Loaded racks--the 'try rack' is on the middle rack, right side

Water evaporates slowly at 80C; however, the color of the fruit is maintained. Drying to 89% weight loss took approximately 7 hours:

Time	Weight	Net Tomatoes	% reduction
00:00	342	290	0%
01:48	247	195	33%
	176	124	57%
04:13	145	93	68%
05:28	111	59	80%
06:28	93	41	86%
07:18	83	31	89%

After 4 hours, tomatoes are shrinking

After 6, the water around the seeds is also evaporating

After 7 hours, the 3.6 kg of tomatoes was down to about 400 grams. Color was excellent, and the light salt gave the tomatoes an excellent taste. (Further note: dipping the tomatoes in flavored salt or smoke would be even more interesting. The liquid smoke extract can also act as a bacteriostat, due to the phenolic compounds in the smoke.)

Summary:

• Starting weight of tomatoes: 3600 grams
• Ending weight : 396 grams
• Water evaporated: 3204 gram (3.2 kg)
• Energy required to evaporate at 2.26kJ/kg = 7068 kJ = 1.96 kWH
• Electricity used in convection oven at 50% cycle for 7 hours= 9 kW
• Overall efficiency = 1.96/9 = 22%

Digital Drying