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Thermodynamics/Osmotic dehydration



I want to dry a tropical tuber with the osmotic dehydration process.
Because it is a vegetable i have chosen the : sodium chloride as an osmotic agent
But i am not able to determine how or where i can find the exact concentration for the solution.
Is it something i can buy? should i make it myself?
How can i do it?

Thank you

ANSWER: Hi Claude,

In order for the osmotic pressure to work solutions have to be quite high(10% NaCl).
However very high solutions (25%) tend to allow salt to enter the fruit.

Addition of sugar (25%) to salt (10%) can have good results.
Another factor is the thinness of the fruit slices.
All fruits behave differently due to water content, sugar(s) content and  losses to the salt.

A little experementation (2-3 hour tests) shuld show you what is best.

I hope this helps.
Best wishes.

---------- FOLLOW-UP ----------

Thank you for your quick answer

As you mentioned, i was thinking about using sugar also in my solution.
-Distilled water
-For the 10% salt: NOT iodized salt (sea salt)
-For the 25% sugar: sucrose

But for measuring,
How do i measure 10% of salt and 25% of sucrose to put in the water?
What tools should i use in this operation (in a practical way)?

Thank you

ANSWER: Hi Claude,

You have to weigh the salt and sugar.

As one gm of water is one ml you can measure water by volume.

On a 100 gm solution accuracy of +/- 1gm will be good enough.

Best wishes

---------- FOLLOW-UP ----------


I did some test and:

I use 10% of salt and 30% of commercial sugar for 210 minutes at ambiant temperature for the osmotic process.

My question:

After the osmotic dehydration process, what do i do with the product before i start with the air drying process?

If there is a draining and washing step, how do i do it? because if i wash it, i am adding water to the product, am i??

I am not clear on what to do and how to do it, between the osmotic dehydration process and the air drying process.

What equipment is best to use in these steps between the osmotic process and the air drying process?

osmotic dehydration------draining-----washing------air drying

I do not understand the draining and the washing, how do i do it?

Thank you very much

Hi Claude,

Draining is easy just put the fruit in a sieve or collander and wait till it stops dripping.

Washing is also easy you need to limit the time in contact with the water to the very minimum.
In the sieve or collander use a water spray for about 30 seconds making sure to stir the fruit.

Drain again as above. Then mop the fruit with paper towels.
Air dry to taste (this will depend on air flow and temperature).

Hope this helps.


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Thermodynamics, chemistry, chemical reactions, kinetics, chemical reaction safety, dust explosion technology, static electricity. General science.


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Institute of Chemical Engineers. Royal Society of Chemistry.

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