We traditionally associate the plum and pear shaped tomato varieties with Paste tomatoes. While this is true to a large extent - not all oval tomatoes are good paste tomatoes and not all paste tomatoes are the oval plum and pear shapes we would expect.
Some Tomato varieties, that in appearance seem to be slicers make for an awesome tomato paste. Appearance alone does not make a paste tomato. Paste tomato characteristics require that they have a low seed to pulp ratio, a higher level of pectin and elevated amounts of sugars and acids. Tomatoes that meet these requirements will also generally have a lower water content.
The lower water content of paste tomatoes makes the juice thicker and creamier which is a quality prized by chefs and Italian grandmothers.
The qualities of a good paste tomato are largely genetically acquired, however these traits can be enhanced by the gardener using optimal growing conditions. Full sun, rich composted soil and warm temperatures, not blazing heat - just warm are some of the conditions which make for the best paste tomato.
Fertilizer - Excessive nitrogen is conducive to excessive lush foliage at the expense of the tomatoes. A little fish emulsion up till their pre-ripening stage is fine so long as you started with fertile soil to begin with.
Best Practices for Best Quality Paste Tomatoes
To enhance the quality of your soil add a modest amount of high phosphorous starter fertilizer at planting time. Crushed eggshells will also help supply needed calcium to your tomato plants adding a handful to each hole when planting outdoors won't hurt. Fish emulsion twice a season shortly after the first blossoms pop up, and again when the plants are laden with green tomatoes. Make sure to dilute liquid fertilizer as most are heavily concentrated and will burn your plants if applied too heavily. Do not fertilize once the fruits have begun to ripen. which is when they've started to turn from green to orange and red.
Up till their pre ripening stage, water them generously. A little mulch can go a long way to retaning moisture and preventing large fluctuations in the soils moisture content. Moisture fluctuations interfere with the plants uptake of calcium which can easily lead to blossom end rot.
As your tomatoes approach maturity, once they have turned a pre-ripe yellow orange color stop feeding them and cut back on watering.
Temperature and Light can also have either adverse or beneficial effects on your tomato plants. There's not much you can do about the temperature, mother nature provides. She won't turn up the thermostat for your tomatoes - it is what it is. You can improve the heat and light available to your plants somewhat with heat absorbing and reflective mulches.
Mulching conserves water in the soil and warms it by insulating the soil. Mulching promotes a healthier root system, and reduces the risk of soil borne diseases. It also increases the soil temperature which is advantageous in cooler sub optimal weather.
Red plastic mulch for tomatoes has some added benefits, USDA and Clemson University researchers discovered that it increased yields up to 20%. Technically, its not really mulch, but it's increasingly used as mulch. Red plastic mulch's success lies is in its ability to reflect red shades of light back to the plant, accelerating fruit production and producing better yields.
Light is something the gardener can have some effect on - a location with full sun is essential to producing the best Paste Tomatoes. At the very least 6 hours daily, preferably more. Using the red plastic mulch described above will help to optimize your plants ability to take full advantage of available light and produce the best paste tomatoes.
Popular Varieties of Paste Tomatoes
San Marzano Tomatoes are true Italian paste tomatoes. In Italy they are grown in rich volcanic soil of Mount Vesuvius. They are the only tomatoes that can be used for Vera Pizza Napoletana - True Neapolitan Pizza. San Remo Paste tomato is a similar variety.
Roma Heirloom Tomatoes are bred for high solids and low seed content, making them firmer. This firmness and low seed count lends itself to canning, sauces and tomato pastes more readily. They are sometimes considered determinate because they bear an initial flush of ripe fruit early, however in many varieties this is commonly followed by indeterminate fruit, which classifies them as an indeterminate.
Japanese Black Trifele is a Russian Heirloom. It has a pleasant rich taste, spicy richness, not an overly sweet flavor. The tomatoes are pear shaped and are a mottled purple color with green streaked shoulders, it darkens to a burnt chocolate color and culminates in an almost completely black base.
Costoluto Genovese Tomato is a ribbed deep red old Italian heirloom. It is flat and rounded not plum or pear shaped, but makes an excellent Paste tomato.
Amish Paste tomato Plum shaped fruits 8 to 12 ounces each with excellent taste appeal.
Powers Heirloom Tomato, open-pollinated, indeterminate Tomatoes are a pale yellow and relatively juicy and sweet. Good for canning, preserving, as a paste tomato. Other than its yellow coloring, Powers Heirloom is very similar to Amish Paste Tomato.
Polish Paste Tomato, goes great with Kielbasa [No not really]. Produces pear shaped fruits up to 1 lb. in size. 6 inch diamete, pear-shaped tomatoes. Ribbed and irregularly shaped that can weigh up to a pound. Full flavored robust paste tomato. Indeterminate vines.
Black Plum indeterminate.
Italian Gold determinate yellow plum-shaped.
La Roma Rossa determinate hybrid. Red, pear-shaped.
Opalka indeterminate; red-orange, pepper-shaped.
Plum Dandy hybrid determinate; red, plum-shaped to 6 ounces.
Verna Orange open-pollinated indeterminate; orange, heart-shaped.
Viva Italia hybrid determinate; red, pear-shaped.