Heirloom tomatoes are dangerous. Beware of eating a slice tucked inside a turkey panini. You risk having to rearrange your entire garden plot to accommodate a gorgeous Red Zebra vine or the drool-worthy Brandywine variety.
Growing heirloom tomatoes in a home garden is a great way to enjoy this savory treat without paying the high price at a farmer’s market, but heirlooms have a short shelf life.
Preserving excess garden produce in cans is effective, and heirloom tomatoes are no exception.
Canning heirloom tomatoes is similar to canning non-heirloom tomatoes, but there are some nuanced differences. In this article, we will address:
- What Makes Heirloom Tomatoes Unique
- Tips for Handling Heirloom Tomatoes Prior to Canning
- Nutritional Value of Canned Tomatoes
- When Canning is Not the Best Choice
Let’s first dive into what sets heirloom tomatoes apart and guidelines for preserving them.
What Makes Heirloom Tomatoes Unique?
Heirloom tomatoes provide a flavorful alternative to conventional hybrid tomatoes which are typically bred for color and durability rather than the flavor factor. Though, in recent years, scientists have worked to improve the taste of commercial hybrid tomatoes. (source)
Bear in mind that not every heirloom tomato plant is delicious. Extra-large tomatoes have a weaker flavor, and some heirlooms turn into a mushy mess within a day of picking.
However, many heirloom varieties taste incredible, and all of them are open-pollinated seeds that have been passed down for decades.
Open-pollinator seeds produce tomatoes that are the same as their parent plant and should be grown separate from other types of tomatoes to prevent cross-pollination. (source)
Because heirloom tomatoes are not bred for ruggedness and high yields, they generally produce fewer fruits and are less resistant to pests, fungus, and disease.
The unique properties of heirloom tomatoes mean you should bear several things in mind when preserving them.
Tips for Handling Heirloom Tomatoes Prior to Canning
Since heirloom tomatoes can be delicate and difficult to grow, it’s important to take care of them and make the most of your yield.
1. Save some seeds!
Seeds from hybrid tomatoes do not produce fruit that’s genetically identical to the parent plant, but open-pollinator seeds are special in that the fruit you see is the fruit you’ll get. If you enjoy your heirloom tomatoes, save some of your seeds for next season and preserve the lineage. See our Step-By-Step Guide to Starting Tomato Seeds.
2. Be gentle.
If you have ever purchased heirlooms, you often have to pick from many bruised tomatoes because their skin is not as thick as typical store-bought hybrids. They are not built for travel.
Heirloom tomatoes have a more delicate skin than conventional store-bought tomatoes, so be gentle with them to preserve your harvest.
3. Do not can bruised tomatoes or those with rotting spots.
Tomatoes with bruised or decayed parts can lead to preserving harmful bacteria which causes illness when consumed. Examine them carefully and only choose firm fruit.
4. Waste no time.
Be aware of the short shelf life of heirloom tomatoes. Promptly can the ones that you do not plan on eating fresh with salads, sandwiches, etc.
Not only does prompt canning preserve flavor and texture, but it also helps to retain a higher percentage of nutrients which decline quickly after harvest.
5. For best results, refrain from refrigerating whole tomatoes.
I know it’s tempting to store tomatoes in the refrigerator because a lot of other produce is preserved that way, but refrigeration degrades tomato flavor.
When tomatoes reach temperatures less than 54℉, the genes stop producing a substance that’s directly linked to the flavor. (source)
Once you slice open a tomato though, refrigerate the remainder.
Don’t be surprised if your canned heirloom tomatoes have a thin texture (perfect for chili). They tend to be less dense than plum-type tomatoes like San Marzanos. When making a sauce with heirloom tomatoes, you might need to reduce them for a thicker consistency.
Are Nutrients Lost When Canning Heirloom Tomatoes?
Did you know it’s possible for a canned tomato to retain higher levels of nutrients than a fresh tomato?!
A tomato that spends days on a truck bed moving from farms to distributors to grocers can lose more nutritional value than a ripe tomato canned the very day someone plucked it off the vine. (source)
That being said, a large portion of the nutrients found in tomatoes (including heirlooms) are lost in the traditional canning process.
Anytime fresh fruits and vegetables are processed, their nutritional value is reduced in some way. Processing includes everything from pulverizing in a blender to canning to cooking on a stovetop.
Even though lycopene, a nutrient in tomatoes, increases during cooking, other nutrients like vitamin C decrease, but the greatest nutritional loss occurs when seeds and skin are removed. (source)
Nutrients Lost by Removing Skin and Seeds
Traditional canning involves skinning and deseeding tomatoes, just leaving the pulp. But, the skin and seeds contain a disproportionately high percentage of the tomato’s vitamins, minerals, and essential amino acids.
A scientific report from West Virginia University states:
“Evaluation of three different tomato cultivars showed that seeds and skin contributed to greater than 40% of total flavonoids, lycopene, ascorbic acid, and total antioxidants.”
Lycopene, for example, is 2.5 times more concentrated in tomato skin than the pulp. Lycopene is a cancer-fighting nutrient that promotes cell communication and regulates hormones, immune function, etc. (source)
Side Note: Even though heirlooms are often superior in taste compared to hybrids, they are not necessarily nutritionally superior. (source)
The Cons of Preserving Skin and Seeds
Tomato skin can be tough and not very sweet. Even when it’s cooked, the skin can be unpleasant to eat. Thankfully, the delicate skin of heirlooms makes ingesting them more palatable if you so choose that route.
Retaining the seedy, watery sections is not texturally or aesthetically pleasing, but you might consider it worth the nutritional value.
There are not yet official USDA procedures published regarding canning tomatoes with the skin and seeds, but perhaps there should be for the exceptionally health-conscious canners.
Is Canning the Best Preservation Method for Heirloom Tomatoes?
Canned tomatoes are convenient to use because they do not need to thaw or be hydrated. They also look awesome on shelves and do not take up freezer space. However, the process of canning is not always the most practical option.
Canning is an involved project, but preserving a bunch of produce at one time is ideal. If your yields are spread out and not large enough to warrant all the effort of canning, freezing might be a better option if you have the space for it.
Freezing is easier. It doesn’t require extra hardware, it’s less time-consuming, and freezing retains nutrients more effectively because it requires less processing. If you make a sauce with the tomatoes before freezing them, obviously the heat will decrease nutrients (except for lycopene which increases).
Both canning and freezing allow for flexibility in terms of form; the tomatoes can be preserved whole, diced, crushed, puréed, as a sauce, etc.
Other ways to preserve tomatoes include dehydration and freeze-drying. These processes require additional equipment. Freeze-drying is the most expensive method, but it’s also the method that retains the highest percentage of nutrients.
Few things prove more satisfying than adorning your shelves with beautiful red jars of your hard labor. Can you can? Yes, you can!
Even though canning does not preserve the highest percentage of nutrients, it is still a great option for preserving heirloom tomatoes. Just make sure to take extra care with the delicate fruit and can immediately after harvest for best results!
If you want details on traditional canning methods, here is the official USDA guide that goes in-depth with exact procedures. There are different time requirements for different altitudes, so make sure to learn the protocol for your elevation.
Related Reading: Poor Farming Practices & How They Affect Your Food