Cooking + Physics question

[tinknal]

I'm curious. I'm cooking down tomatoes to sauce. This requires the evaporation of a large amount of water. I'm wondering what the most efficient way to do this is. Lid on, no vent, lid on vent open, or no lid.

If In remove the lid more heat will escape. If I leave the lid on less steam will escape. Aside from opinions does anyone have any science that will shed light on this issue?

[Vicki McGaugh TX Nubians]

I have no idea about the science but common sense would say that when you a reducing down anything you keep the lid off so the moisture escaping doesn't condensate on the lid and simply fall back into your sauce. Another trick is to seed the tomatoes first...cut them in half, gently squeeze out the seeds which also drips out the juice...just don't squeeze to hard or you will loose some pulp. I always peel my tomatoes for sauce since the skins can make your sauce bitter. To peel tomatoes just dip them quickly in boiling water, dip not cook. Vicki

[georgec]

Simple physics/chemistry tells you that water boils at 212 degrees F, at sea level. Now if you put a lid on this will raise the pressure slightly thus raising the boiling point, and you will get less evaporation from the liquid, you will also get condensation which will take energy out of the steam thus lowering the temperature. You want maximum evaporation, leave the lid off.

[LagoVistaFarm]

On a practical note. Heavy bottom pot with a large flame works the fastest. No lid.

[tinknal]

Originally Posted by LagoVistaFarm

On a practical note. Heavy bottom pot with a large flame works the fastest. No lid.

Well, I'm using an electric cooker.

[tn_junk]

Puree' the tomatoes and let them sit overnight in the fridge. A lot of the water will come to the top and can be poured off. Saves cooking time.


galump

[bill not in oh]

Take a lesson from the maple syrup industry... large surface area and relatively shallow containers. Tomato sauce is probably easier to scorch, but that would have to be the cook's responsibility to monitor the heat - lowering it as the sauce thickens...

[MELOC]

Originally Posted by bill in oh

Take a lesson from the maple syrup industry... large surface area and relatively shallow containers. Tomato sauce is probably easier to scorch, but that would have to be the cook's responsibility to monitor the heat - lowering it as the sauce thickens...

what he said. if i had a lid on my evaporator pan, i would have to cook the syrup for days. also, and just as a point of science, as the mixture thickens, it's sugar content probably increase and the boiling point rises...just like syrup.

[moonwolf]

no lid, simmering heat, large pot.

[Cindy in KY]

I run them through the puree machine, and cook them in a large crock pot on low with the lid ajar, so the steam escapes. Never sticks or overheats. Overnight in the fridge sounds like a really good tip, thanks! I am still putting up lots of tomatoes.

For chunky tomatoes, I just wash, core, and put in chopper, skins on, and chop to salsa size, and then funnel into 2 & 3 liter pop bottles. You can make a funnel from a smaller pop bottle upside down, cut the bottom off. I put these bottles in the bottom of the freezers to cook later.

[Christiaan]

We use the Maslin pan available from Lee Valley http://www.leevalley.com/
You can get the temperature quiet high without worrying about scorching. The pan gets wider from the base to the rim and is excellent for making sauces, jams, and jellies. It also makes a great soup and stock pot.

[Farmerwilly2]

Someone on this site offered a method we weren't able to try because of our drought this summer, but it seemed like just the ticket. They run their tomato through a mill, dump the puree into a clean chest cooler with a bottom drain. They float a couple frozen 2 liter bottles in it to keep it cool. When time has past for the puree to separate they drain water from the bottom. This would greatly reduce the amount of water needing to be evaporated on the stove, lessening the chances of scortching.

[goatsareus]

I separate the tomato "water" from the tomato pulp before it reaches to simmering pot. This greatly reduces the amount of cooking time, by about 90%!

Quarter tomatoes into a large kettle that has 1/4 inch of water in the bottom. Once all the tomatoes are in the kettle, turn on heat, and cover kettle. Do not stir, squish, mash, or touch the tomatoes. Simmer until the top layer of tomatoes are soft. This will vary depending on how large a kettle you have, from 40 to 60 minutes. Turn off heat. Carefully ladle cooked tomatoes into a colander to drain, at least one minute. Draining time will affect the thickness of the finished product, longer draining, thicker the sauce. Dump this pulp into a blender and blend until smooth. Pour this into a pot to heat to boiling. Can as desired.
I use this method for canning pizza sauce and bbq sauce.

[Cyngbaeld]

Save that tomato "water" for juice!

[Cyngbaeld]

Original question about energy. Since you are evaporating it is more energy efficient with the lid off. Evaporating requires a specific amount of heat to change the state from liquid to gas and you want this gas driven off. You do not want it cooling and returning to liquid to drip back into the pot. When it cools more heat is lost thru the lid of the pot without accomplishing the original task. You also have to consider that the change of state will occur at a lower temperature if the vapor pressure is lower. Having the lid on increases the vapor pressure. If you have a small fan to direct at the top of the pot the liquid will evaporate somewhat faster.

[goatsareus]

Originally Posted by Cyngbaeld

Save that tomato "water" for juice!

This year I added about 3/4 cup long grain brown rice and canned that with the juice, worked out nice..

[ailsaek]

I put the lid on to get it to the boiling point, then once it gets simmering I take it off. I also put in quartered tomatoes, with nothing removed. Yes, it's more energy intensive, but I figure I lose fewer nutrients that way. Once they get soft, I run them through the Foley food mill and then cook them until they're as thick as I want them.

[FrankTheTank]

Doesn't the food industry use corn starch or something to displace the water?

[ailsaek]

Cornstarch doesn't displace water, it soaks it up and gels.

[tinknal]

Originally Posted by ailsaek

I put the lid on to get it to the boiling point, then once it gets simmering I take it off. I also put in quartered tomatoes, with nothing removed. Yes, it's more energy intensive, but I figure I lose fewer nutrients that way. Once they get soft, I run them through the Foley food mill and then cook them until they're as thick as I want them.

This is exactly how I do it. When do you add the seasonings?