8 Jun 2005

Tomato foam

The Norwegian cook, food writer and weekly source and inspiration (at least to me) Andreas Viestad wrote a fascinating piece on tomato mousse:
Run a tomato or three (cut in pieces) in a blender for five minutes. Running for a shorter time will not give the desired result even though it seems finished. Pour into a bowl and leave for a few hours and you get a mousse-like pink jelly. With reference to prof. Hervé This he guesses that the reason may be liberation of pectin from the crushed tomato skin. Pectin is a natural occurring acidic polysaccharide/carbohydrate which contributes to stiffness in some fruit/berry jams and jellies.

I tried this with moderately satisfactory result; a fairly ok foam/mousse on the top with a more soggy mass at the bottom of the glass.

If pectin is the big point
- using ripe tomatoes should give poorer result that unripe (or less ripe) as the pectin is broken down during ripening. This is by the way the reason why you should use not very ripe berries/fruit when making jam/jelly and more ripe when making juice/syrup. Vice versa: ripe/unripe tomatoes should not make a difference if pectin is not involved.
- Pectin is located in the skin, cell walls and between cells of the tomato. Breaking the cell walls (destroying the cells) by blending should therefore not be a critical point.

If breaking the cells walls is of vital importance
- freezing the tomatoes should be very effective in breaking the cell walls as expansion and formation of sharp crystals by loads of water inside the tomato will cut/explode the cells from within. After freezing, long blending time should not be necessary. Why this should be, I'm not sure. A biologist colleague meant that a possible reason may be that enzymes within the cells are liberated and can react with other parts of the tomato.

Suggested (comparative) experiments:
For consistent experiments, the same blender speed should always be used, and the container should be rinsed between each blending. Washing unnecessary? (most of the tomato is water soluble, but important compounds may be water insoluble)

1) Blending time - cut four tomatoes in two and divide in two heaps (two halves from the same tomato in each group). This way, I'll have to identical heaps. Run one heap for 1-2 minutes, the second for at least 5 minutes. Pour into separate bowls and leave for a few (3-5?) hours.

2) Breaking cell walls - cut four tomatoes in two and divide in two heaps as above. Put each heap in a plastic bag, leave one in the fridge and the other in the freezer overnight. Thaw the frozen tomatoes and run each heap in the blender for an identical period of time. Pour into separate bowls and leave for a few (3-5?) hours.

3) Ripe vs. unripe and blending time double experiment - this is a little less stringent that the point above, but worth a try. You need ripe and unripe (less ripe) tomatoes, ideally from the same plant (grow your own). Make four heaps:
a1) Ripe + short blending time
a2) Ripe + long blending time
b1) Unripe + short blending time
b2) Unripe + long blending time
Run the four heaps separately as for 1). Pour into separate bowls and leave for a few (3-5?) hours.

I'll have to follow up this some time soon (maybe wait for our own tomatoes to ripen?). Results and reflections will be published.


Addition 11. May 2010: Report from The Flemish Primitives 2010 by Martin "khymos" Lersch has some interesting and possibly relevant info on this matters as well as references. Maybe a solution is to be found therein?

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