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Blog : Preserving Tomatoes in Glass Jars is Indeed a Process. Blog : Preserving Tomatoes in Glass Jars is Indeed a Process.

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Preserving Tomatoes in Glass Jars is Indeed a Process.

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Quarts of San Marzano tomatoes 600w Tomatoes are many things - luscious, sweet, tart, beautiful, smooth and silky, even sexy.  It is no surprise then that this beautiful fruit can also be dangerous.  When it comes to putting up (canning, preserving, jarring) tomatoes, we look to the pros - the uncontested authors of the Slow Food Movement and quiet authorities on managing all things voluptuous... 

We look of course, to the Nonnas.  Generations of Italian and Italian-Canadian grandmothers, charged with providing for large families year-round, using only what they grew, preserved and prepared with their own loving, cautious hands.  Nonnas know about tomatoes.

From Nonas and from hundreds of their passed down and along recipes, scribbled notes and tales told around the table, we've learned how to put up tomatoes safely. Once we knew to be cautious, the science was easy:  if the required acidity and pH are not achieved before processing, tomatoes and other low-acid foods like green beens, corn, beets and asparagus, can produce illnesses such as food-borne botulism. The high-heat associated with hot water canning is not sufficient to kill certain pathogens in a low-acid environment, so correcting the environment is an easy fix.

Washing San Marzanos outside sink 600w

Many tomato varieties, like the meaty vine-ripened San Marzanos we love (above), are very sweet when ripe. This in turn means they generally have medium-low acid and a pH  of 4.5-5.2.  To safely preserve tomatoes for future use, a pH level below 4.6 must be achieved.  This can be done with bottled lemon juice or vinegar.  Organic lemon juice is best.  Fresh lemons are not a reliable source as sweetness and acid vary by variety (ie: sweet Meyer lemons).  Bottled vinegar should be 5% acetic acid by volume.  Salt too, should be added. 

It is impossible to test every variety and batch of tomatoes before canning, so we rely on a gold-standard that seems to work across the board and ensures a neutral tomato canvas from which to work your culinary magic.  For every quart of whole or crushed tomatoes, we add one teaspoon of salt (we use Sicilian sea salt) and 3 tablespoons of white wine or cider vinegar, or lemon juice.   This acid-balancing, plus a slow ascent to 212F on the stovetop, and an old-school hot water bath of the extended variety, take some time to be sure, but they also take the worry. And that, as any Nonna will tell you, is well worth the wait.

To Preserve Old School Tomatoes in Glass Jars

Our shopping list: Tomatoes (approximately 2.5 lbs/1.25 kilos yields one quart), bottled lemon juice or any variety of 5% acid white vinegar (5% acid), and salt.  We estimate the quantity of acid required by calculating 3 tablespoons per quart.  Likewise with salt, using a ratio of one teaspoon per quart.  Use sterilized chip-free glass quart jars with screw rings and (new) seals.

Wash tomatoes.  Remove stem, core and any blemishes.  When removing black blight marks, be sure to check the flesh beneath as a small surface blight can actually contaminate an entire tomato inside. Rinse tomatoes and compost trimmings. We can outside rain or shine, using a much-loved but beat up old enamel-top canning table, set next to an outdoor sink and grill.

Peeling San Marzanos canning table 600w

Set a large pot of plain water to a rolling boil. Set trimmed tomatoes to the left of the pot and three bowls to the right. The first bowl should contain 50/50 ice cubes and cold water, and the second two bowls should be empty.   Working with three trimmed tomatoes at a time, drop fruit into boiling water and wait for up to one minute or until you see the skin crack and begin to peel away from the flesh at the cut end.  Remove tomatoes quickly from the water and plunge them into the icewater bath. This hot/cold process is called blanching.  Peel blanched tomatoes over the second bowl.  The skin should fall away using just your fingers. If it does not, drop the tomato back into the boiling water for a few seconds. Note that skin sticks stubbornly to un-ripe spots, and unripe tomatoes are harder to peel.  Place peeled, whole tomatoes in the third bowl. You'll develop your own rythm. Three at a time works for me.

Over the years, trying different methods and making mistakes along the way, we've come to a standard three types of naked tomatoes (no basil, no spice, no olive oil added before canning) - thin, medium and chunky.  The integrity of the tomatoes you put into the cooking pot, before bringing to temperature, determines what goes into the glass jar. However, every type of tomato will render and process differently, so just because we suggest you will end up with whole/chunky canned tomatoes in the end, does not mean that you will.  Uncertainty is part of the fun!

Peeled San Marzanos in pot on stove 600w

On this day, whole tomatoes begat whole/chunky preserves, halved tomatoes (above) begat medium preserves, and hand-crushed tomatoes begat a thin sauce-like preserve.  Most recipes using whole canned tomatoes, suggest cooking times that render the pulp completely, ultimately, so plan accordingly and be flexible regardless.

Use a heavy-bottom dutch oven or stockpot to bring the tomatoes to boil slowly under their own steam (do not add water) with the lid on.  Stir very gently and only as neccessary to prevent scorching.  A good quality enamelled pot like La Creuset should allow you to bring tomatoes to boil almost without stirring.  Another trick is to use a new or vintage cast-iron griddle as a simmering plate, to displace heat evenly and prevent bottom-burn.  The less disturbed your tomatoes are during heat up, the less they will break apart.   The halved tomatoes shown above were brought to boil with little disturbance and remained (below the juice risen to the top), largely intact. 

Cooked San Marzanos in pot on stove 600w

Hint:  Mark your stockpot inside and out at each quart level, using a permanent marker.  You could argue for or against marking a precious pot (our large 14-quart stainless stock pot is indeed scarred but the marks make for great memories).  Marking allows you to calculate, add and thoroughly incorporate acid and salt in quantity** before canning, rather than quart-by-quart* as you fill each jar.  

Fill hot, sterilized jars with hot tomatoes, using a sterilized ladle and funnel.  Fill to within 1/2 inch/1.25 cm of top edge of jar - this rule is important to adhere to as it affords optimal expansion/contraction space to create safe vacuum seal (and no underwater explosions), and also ensures that food does not touch the lid fo the jar during processing and storage.

If using the quart-by-quart* method of balancing, add three tablespoons of lemon juice or vinegar and one teaspoon of salt to each half-full jar, then continue filling with hot tomatoes.  If using the quantity** method described above to add acid and salt during initial heating of the tomatoes, do not add anything additional as you fill the jars.

Use a sterilized rubber or plastic wand to agitate any air bubbles to the surface (do not use metal as jars can crack).  Wipe top edge of glass jar with a clean lint-free cloth dipped in boiling water (re-fold and use fresh clean surface of cloth for each jar). Place hot sealing lid on clean glass surface and twist on screw-ring. Hand tighten only - do not over-tighten.

Quart jars of tomatoes in hot water bath 600w

Process immediately in hot water bath for 50 minutes.  Add filled hot jars to boiling water, gently, ensuring that jars are submerged by two inches.  Begin timing when water returns to boiling.  Cover and check water level occasionally.  Top-up with already boiling water as needed.  After 50 minutes, uncover pot and turn off heat.  Let jars sit undisturbed for 10 minutes, then remove with jars with tongs and place on a cooling rack for one full-day before disturbing or labelling.  Check sealing lids to ensure that the convex bumps in the centre of each lid has been sucked down to flat (slightly concave) to create an airtight seal.  As jars cool, you will likely hear the telltale 'pings' that indicate success. Unsealed jars of tomatoes should be used immediately or placed in the fridge and used within a few days.

The beauty of preserved naked tomatoes, is that they are gastronomically neutral.  On a whim, we can create Italian, Moroccan, Asian, Greek, Thai, Mexican or Cajun influence.  Naked tomatoes can be reduced, expanded, embelished, cocktailed, filtered and otherwise fetted as you wish, without prejudice.

On this day, in homage to the generations of Nonnas who inspired and keep us safe, we stayed as close to home as we could.  A simple week-day Sunday sauce of sorts started with 1/2 cup (125ml) extra virgin Olio Classico from Domenica Fiore. Use the best extra virgin olive oil you can find.

Sunday Sauce on stove 600w

A half-dozen small cloves of Persian Star garlic from a local organic farm, were poached low in the oil, covered, for almost one hour.  We added a quart of chunky San Marzano tomatoes then let that simmer down for another hour, watching it turn from foamy bright pinky red, to shiny copper mahogany.  We finished with a pinch each salt and crushed dried home-grown cayenne pepper.  Just before serving over home-made, hand-cut durum semolina and egg pappardelle, we stirred in a handful of fresh-picked oregano and basil leaves.  Nothing else needed after so much love and time in.  No cheese, no fancy, no nothing at all!

This blog post is based on personal experience and successes to date.  Preserving tomatoes and other fruits and vegetables requires careful research and planning, and the published rules and recommendations change frequently and with varying altitude (literally).  Always check Canada's Home Canning Safety Recommendations before proceeding with this or any home preserving or home canning project.

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