You just unearthed some veggies from the depths of your fridge, and they look … tired. What can you do to them?
Answer : just soak them.
In the prefect world, we would go to the farmers’ market daily, to buy leafy, green veggies that have been harvested hours before, then cook and serve them that same day to our happy families.
But I am a real person. When this photo was taken, this batch of Nai Bai had been in the fridge for a week. A WEEK. Despite being wrapped in newspaper and bagged, they were limp and uninspiring, hardly the kind of produce a foodie wants to show.
I had noticed that leafy vegetables seem to perk up considerably after being washed, especially if left to soak for a while. However, I didn’t take this seriously. When this was mentioned by Chef Michael Smith as a way to perk up salad leaves, I started observing my veggies more closely. It was obvious to me that the method worked, but to understand more I carried out this food lab.
Veggies go limb mainly because of moisture lost. In the living plant, water lost by transpiration is replaced by uptake from the roots. Once harvested, the moisture loss continues, but with no replacement, the veggies lose their form. Soaking should work, if the water lost can be reabsorbed by the veggies.
To gain some insight, my advanced instrument is ……. the weighing scale. Weigh the vegetables before and after soaking, and I should have a good indication what is happening.
The experiment
I timmed the veggies, and separated them into individual leaves as I would for a stir-fry. I then took their weight. 92 grammes. (Yes, I tared the basket).
You can see how the veggies barely fill the basket, and the leaves limb and uninspiring.
I washed the veggies under running water, then left them to soak in room temperature water for ten minutes.
After the soak, the difference was immediately obvious to the hand and eye. The leaves felt crisp and had obviously perked up. You can see how they now fill the entire basket. What surprised me was the weight. I carefully shook off as much of the water as I could. When the soaked veggies were weighed, the scale registered 127 grammes, up from the 92 grammes before the soak. 35 grammes of water has been absorbed, over one third of the original weight of the veggies! As I had taken pains to flick the veggies dry, the weigh gain can only be explained by the water absorbed into the veggies. There simply can’t be 30 grammes of water clinging to the veggies.
And just look at how much better the veggies look now.
Soon after their bath, the veggies were fried up. I had nice veggies for my meal and avoided waste.
Summary:
Weight before soak : 92 grammes Weight after soak : 127 grammes Water gain : ~35 grammes
Conclusion
This certainly works! Eat veggies fresh if you can, but if not, store them well, and soak them just before you use them. This should work for any leafy veg, for stir fry or a salad.
Scientific Basis
The mechanism of water absorption is not clear. Living plants do not generally take in water through their leaves, as the flow of water is from the roots to the leaves. It is possible that all the water intake is through the cut ends of the stems. However, in this experiment the water is absorbed very quickly. I hypothesize absorption has to be through the large surface area of the leaves, likely first via the stomata, and then into individual cells through osmosis. There will be a higher concentration of solutes within the cells, which would cause water to be drawn into the cell. This builds up turgor pressure as the cells expand against the cell walls, making the stems and leaves rigid. Further experiments are needed to pin-point the precise mechanism.
Note on storing veggies
The metabolic processes in veggies continue after harvest, as does water lost. The result is veggies turn yellow, and shrivelled.
The metabolic processes are slowed by low temperatures, and moisture loss is reduced in a humid environment. Storing leafy veggies is a balance. They should be chilled but not frozen . They should be kept in a humid environment, but liquid water should not accumulate. The water droplets can cause rotting and darkening.
My storage method is to first wrap in newspaper, and then to place the parcel in a plastic bag. The paper absorbs the liquid water, helping to keep my veggies happy.