The last long form article discussed the effects of salt on meat via brines and marinades. The purpose of salt usage in meat is to help the meat retain moisture to yield juicy results, particularly in leaner cuts. We also discussed its use in obtaining crispy skin in chicken. Osmosis and diffusion (water and salt moving from areas of high concentration to lower concentration as an equilibrium is sought) are the primary mechanisms by which we achieve these results. In this month’s food chemistry article, we’ll examine how these same mechanisms act on vegetables.
While we seek juicy meat, we generally prefer the opposite in our vegetables. No one likes a soggy coleslaw, a floppy vegetable tart, or water-logged eggplant dishes. Our culinary goal in dealing with water-heavy vegetables (and sometimes fruits) is to remove this excess water, and we’ll achieve this using the same principles of diffusion by salting the vegetables.
How does salt draw water from vegetables?
The walls of plant cells are made of cellulose, and these walls get thicker with age. The cellulose walls are the reason raw vegetables are so crunchy. Sometimes this is desired, sometimes not. Between the cells is a set of polysaccharides (a type of carbohydrate) called pectin, which helps the cells bind together and maintain the plant structure. Importantly for our purposes, pectin is water-soluble, meaning that it dissolves in water.
Water is contained inside the plant cells of many vegetables (even broccoli, which seems stiff and crunchy). When we salt vegetables, we create a higher ion concentration of sodium and chlorine ions on the surface of the vegetable compared to the inside of the cells. Since nature seeks equilibrium, the natural “desire” is to balance the concentrations of ions inside and outside the cells. Thus, the water inside the cells is pulled out through the cell walls, which are permeable. This is osmosis, and the astute reader will recognize that this is the same beginning phenomenon that occurred when we discussed salting meat.
Unlike salting meat, where we leave the salt on and let the salt water at the surface diffuse back into the meat, we wick the moisture away from the vegetables once the water has been drawn out. Patting the excess water off the vegetables after salting will remove most of the salt as well.
Besides removing the excess water from the vegetables, we also induce a change in texture by salting. The strength of pectin comes from calcium and magnesium ions within the different polysaccharides. When we salt vegetables, the sodium ions replace these calcium and magnesium ions, which weakens the pectin’s structure, softening the vegetables.
Why do we want to do this?
Excess water in a recipe with vegetables can ruin the flavor and texture of many different dishes. Dressings get diluted, baked goods get floppy, and a good vegetable lasagna becomes a bland pool of tepid tomato sauce.
What vegetables benefit from salting prior to use or cooking?
Summer vegetables in particular are made up primarily of water. These include
- Tomatoes (culinarily, they are considered vegetables even if they biologically are fruits)
- Cucumbers
- Zucchini and yellow squash
Other vegetables that benefit from salting in some recipes include
- cabbages
- eggplant
- broccoli
How long should the salting take?
This depends on the vegetables, and how much water you want to draw out. For a vegetable gratin, which uses many different types of watery vegetables like tomatoes, yellow squash, and onions, a recipe may call for salting the vegetables for 30-45 minutes prior to doing anything else to draw as much moisture out as possible. For a salad or slaw, you’ll want to salt the vegetables for several hours. For a quick dish of sauteed shredded summer squash, 5-10 minutes will suffice. Be sure to carefully read recipes and plan ahead.
Salting Also Makes Vegetables Taste Better
We taste food with our noses and tongues, when chemical substances called aromatics activate nerve cells on the tongue and in the nose. This means our tastebuds must be physically exposed to these chemicals in order for us to perceive taste. Many of the aromatics that flavor vegetables are trapped inside the cell walls, and are also bound to proteins inside the cells that render them inaccessible to the receptors on our tastebuds. Chewing food releases some of these flavors, but not all. Salt draws these flavors out of the cells and also forces a separation of the flavors from their protein-prisons so that we can have access to more of these molecules. However, this takes time, and the flavor compounds are drawn with the salt into liquid, so this works best when the liquid will be retained, as in a soup.
Are there any nutritional effects of salting vegetables?
Some nutrients, such as Vitamin C, folate, riboflavin, and niacin, are water-soluble. These compounds may be drawn out during salting or subsequent cooking and lost, particularly if the liquid will not be used in the final dish. Fat-soluble vitamins such as Vitamins D, K, and E are less effected, and in fact are absorbed more easily when the vegetable is cooked in oil. Ultimately, both salting and cooking (since salting replaces magnesium and calcium ions) will deplete some nutritional compounds in vegetables.
Recipe: Stuffed Tomatoes with Parmesan, Garlic, and Basil (Serves 6)
Ingredients
- 6 firm, large, ripe (but not too ripe), round tomatoes. (Should weigh about 8 ounces each)
- 1 tsp kosher salt
- 1 slice sandwich bread, torn into quarters
- 3 tbsp olive oil
- 3/4 c. Parmesan cheese, grated
- 1/3 c. shredded fresh basil (Do not substitute dried basil here; dried basil is generally flavorless compared to fresh.)
- 2 minced garlic cloves
- pepper to taste
Equipment
- baking sheet
- food processor
- 9″ x 13″ glass baking pan
Instructions
- Slice about 1/8 inch off the stem end, core, and seed the tomatoes.
- Line a baking sheet with a double layer of paper towels
- Sprinkle the inside of each tomato with same and place upside down on the baking sheet. Let sit for 30 minutes to remove excess moisture.
- Preheat oven to 375 F.
- Line the bottom of the glass baking pan with foil.
- Pulse bread in a food processor to coarse crumbs and toss with 1 tbsp. olive oil, cheese, bails, and garlic.
- Pat the inside of the tomatoes dry with paper towels (gently).
- Arrange the tomatoes in a single layer in the baking dish, and brush the top edges of the tomato with 1 tsp. olive oil.
- Stuff the tomatoes with about 1/4 c. filling and drizzle with olive oil.
- Bake about 20 minutes. (The tops should be crisp and light brown.)
Sauteed Shredded Zucchini with Garlic and Lemon (serves 4)
Ingredients
- 5 zucchini, halved lengthside, seeded, and shredded (Use a box grater.)
- 1.5 tsp salt
- 1 slice sandwich bread, torn into quarters
- 2 tsp lemon juice
- 1 minced garlic clove
- pepper to taste
Equipment
- box grater
- kitchen or tea towel
- 12″ pan
- colander
Instructions
- Toss zucchini with salt in a large bowl, then transfer to colander and let rest for 5-10 minutes.
- Place the zucchini in a towel and wring out the excess moisture.
- Move the zucchini into a bowl and separate clumps.
- Add 2 tsp olive oil and minced garlic to the zucchini and toss to combine.
- Heat 2 tsp ghee or bacon grease in the pan over medium-high heat until just before the smoke point.
- Add the zucchini and cook in an even layer without disturbing until the bottom is browned (about 2 minutes)
- Stir well, breaking clumps, then continue cooking until the next bottom layer browns, about 2 minutes more.
- Remove from heat and add lemon juice, and additional salt and pepper to taste.
- Drizzle with good olive oil, if desired, and serve immediately.
References
- Crosby, Guy (2012). The Science of Good Cooking. America’s test Kitchen. ISBN: 978-1-933615-98-1
- Lanman, F. Minton, E. “The Effect of the Use of Salt in Cooking Vegetables”.Ohio Agricultural Experiment Station, Bulletin 406., (1927).
- Moncel, B. The Spruce Eats.(2019).
- Vernin, G. The Chemistry of Heterocyclic Flavouring and Aroma Compounds (1982). John Wiley and Sons.
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