Osmosis in the kitchen

Lettuce should be fresh and crisp but upon storage water will eventually evaporate. The pressure inside the cells drops and the leaves shrink and become less appetizing. The simple yet effective remedy is to immerse the lettuce leaves in plain, cold tap water. The water will then diffuse back into the cells again. The process is known as osmosis [wikipedia].

For the following experiment I purposly left some lettuce (Lactuca sativa var. crispa, sold in Norway under the name “Rapid”, it’s a Summer Crisp/Batavian cultivar) to really dry out as you can see from the picture.

After approximately 4 hours in water the leaf looks like this. Notice that along the rim the leaf was so dry that the cells were damaged “beyond repair”.

To illustrate this relatively slow process I set my camera to take a picture every minute and left it for almost 4 hours. I then stiched it together and the resulting time lapse movie shows the process speeded up 720x (click if the embedded video won’t work).

The wonderful thing about this simple experiment is that it actually illustrates the essence of a recently rewarded Nobel prize (and I should thank Erik Fooladi for pointing this out to me)! The 2003 chemistry prize was awarded “for discoveries concerning channels in cell membranes”. The swedish Nobel foundation have excellent pages with further explanations for the public and for specialists alongside an illustrated presentation (recommended!). There are even two animations of which the first is also available on youtube (embedded below, poor resolution, download the original for higher resolution!). It shows how water molecules move through cell membranes:

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Filed under: experiments, molecular gastronomy, science, tips & tricks


  1. katie Says:

    So cool!

  2. Magnus Alvestad Says:

    What spices/flavors could you put in the water, that would follow the water into the lettuce?

  3. Martin Lersch Says:

    None. The water channels through the cell walls are tiny and will only let water pass through. In fact, what happens if you add salt to the water is that you can make the water go the other direction, given that the salt concentration in your water bath is higher than the salt concentration inside the cells.

    To demonstrate this, take lettuce leaf and put it water to which you have added 1 T salt. Within minutes it will start to shrink. This might not to be of any gastronomic interest, but it is! I’ll blog on that later.

  4. Laurel Says:

    What else can dehydrate and rehydrate like this? Apples, carrots, humans? What happens when you soak yourself in water for 4 hours? I am curious how this science can be applied in other areas…

  5. matt newby Says:

    Would effect would this have in a “storage” length of time in the walk in? Would this be a preferable method to the cardboard box with a plastic bag inside that the big box suppliers use?

  6. Martin Lersch Says:

    Laurel: Yes, you can dehydrate many foods with salt. Salt has been used for preservation for thousands of years, for example for fish and meat. But I doubt that apples would taste very nice though if preserved with salt…

    matt: I’ve noticed that lettuce which I’ve left in water for several days somehow loses it’s color. So it wouldn’t be a good idea to store lettuce in water. The plastic pack is quite optimal as it ensures a humid atmosphere to prevent/reduce evaporation.

  7. Evil Says:

    Molecular physiology is still physiology.

  8. Seiji Nakatani Says:

    I have not done any thorough research/experiments on this, but I thought water temperature was important. I refresh lettuce in cool, but not cold water. Not sure of the exact temperature, but the thought is to simulate spring/summertime rain. That seemed to rehydrate the lettuce well. I then “crisp” the lettuce by letting it soak in very cold water. Do you think I am taking unnecessary steps? I guess I should hold my own experiment. (smile)

  9. Osmosis resurrection « The h bar Says:

    [...] is it with osmosis and resurrection then? I learnt about this nice experiment in this post in Martin Lersch’s blog. If you leave salad out of the fridge in a hot day, it will slowly [...]