Conference turris::cooks

    
    I find that:
    
    	a.)  Arrowroot has NO taste ...
    
    	b.)  Don't buy a "little" jar of arrowroot ... it's
    		really expensive that way ... find a Health
    		Food Store ... and buy a bagful.  SIGNIFICANTLY
    		cheaper.
    
    	c.)  Don't know about calorie count .... maybe that's
    		why I look like I do  [8;)
    
    /phil/
    

I remember reading that as far as thickening is concerned, 1 tsp arrowroot = 2 
tsp cornstarch = 3 tsp flour.  I believe they are roughly the same 
calorie-wise, so to get to a desired thickness, arrowroot is the lowest 
calorie thickener.

Now, I have been having trouble finding arrowroot lately, and picked up some 
tapioca flour at Joyce Chen's.  Anyone know how this fits into the scheme?

Alright, I'm confused, maybe someone can explain this to me.

How does flour (or cornstarch) work as a thickener?  What is really
going on?

Some recipes (white sauce, gravy, etc) require that you heat
some amount of fat, add an equal amount of flour, cook, and then
slowly add other liquid.  

Some recipes require that you mix cold liquid to dissolve the
flour or cornstarch, and then add it to the rest of whatever you
are thickening, and heat it all up.

What is the difference between these methods?  The latter seems
preferable, because it means you don't have to add fat.  But the
former seems to work more to actually thicken things.

I can *usually* manage a white sauce by the recipe.  Changing 
anything (more flour, less fat, some other liquid other than fat)
screws it up entirely and I end up with a gooey mess - what's
really happening when I mess up?

Say I've got 2 quarts of soup, and I want to thicken the soup
with flour or cornstarch.  What should I do?  What's the difference
between "binding" and "thickening"?

I've heard that half as much cornstarch is required as flour - does that
mean I also require half as much fat for the white sauce method?
How would I use tapioca?  What other thickeners are there?  What
about whole wheat flour or non-wheat flours?

Thanks in advance!
D!

    Potato starch thickens even better than cornstarch - one of the few
    really useful things about Passover cooking (which is otherwise a huge
    amount of work for food that is not as tasty as what I normally
    make.... good thing the holiday is only a week long!).
    
    If I am going to thicken something by making a roux (cook flour in some
    kind of fat), it is usually something that is not transparent anyhow,
    like a white sauce or cream-type soup.  If some liquid is clear,
    thickening it with a slurry of cornstarch and water (or potato starch
    and water) will leave it clear again as soon as the cornstarch cooks.
    I do not normally measure the ingredients, either way.  If you add a
    lot of flour or starch, the result will be thicker and gooier.  The
    consistency is less sticky and more gloppy if you thicken with a
    slurry.
    
    I don't think the amount of fat in a roux matters a whole lot other
    than to cook the flour - I never measure it anyhow.  You can definitely
    use any kind of flour that has starch in it - I often use whole-wheat
    flour - but you can of course taste the difference.  It doesn't matter
    what kind of oil you use, either - I use olive oil unless the taste
    would be a problem, when I use canola oil instead.  You need about as
    much oil as flour in order to cook the flour, but it is not critical
    that you measure either one.
    
    If you use a slurry to thicken something, mix it up good, or you may
    get lumps.
    
    Some sauces are also thickened with an egg yolk.  If you do this, beat
    the yolk well, and then mix in some of the sauce being thickened before
    mixing the egg yolk into the sauce.  It is best to take the pot off the
    burner to do this, and do it quickly with a wire whisk, or you are
    likely to end up with threads of egg (OK if you're making egg-drop soup
    or such, but not so attractive otherwise).
    
    I don't know WHY these things act to thicken liquids - never worried
    about that, so long as they do the job.
    
    /Charlotte
                                

My understanding is that the starch particles absorb liquid and expand
to many times their original size. If they additionally start to stick
to each other, you get something which resembles "polymerization", and
which causes the liquid to start to take on a gel-like consistency
(this usually isn't what we want!).

Cornstarch has a very mild flavor, and can be added raw. Raw flour has
a strong flavor, so cooking it for a short time in fat (to make roux)
cuts this strong flavor. Also, I'm told that this pre-cooking "opens
up" the particles to allow them to absorb water (and therefore thicken
the liquid) earlier than if they're raw.

So, being concerned about fat and calories, does that mean I can 
thicken something equally well with straight flour or cornstarch
without having to make a roux (ie: add fat)?  I know cooking 
it is necessary to get rid of the taste - but, as in the case
of the soup example, can't I add the raw cornstarch or flour to
the soup, and then cook the whole soup?  (Obviously I'd have to
dissolve it first to avoid lumps.)

Can I make a roux without fat at all, using a small amount of
some other liquid in equal amounts with the starch?

Where do I get potato starch?  You mention passover, so would I
check the Jewish foods section (what's the name of that branch,
Maneschwitz)?

D!

    D!,
    I thicken defatted meat drippings with cornstarch and cold water to
    make gravy.  I never use flour, since it always lumps.  If you want to
    thicken something, potato or corn starch in COLD water works best. The
    only time I ever make a roux is when a recipe calls specifically for a
    cream "sauce", like the white lasagna recipe somewhere in thsi file. 
    If you are on a calorie-restricted diet, you won't be eating cream
    sauces anyway : )  But, if you absolutely must, try substituting skim
    milk instead of cream.  Works just as well.  In my experience, the
    starches mixed with water "thicken" an existing liquid.  The roux is
    the "beginning" of a sauce (cream, wine, mixed with beef stock for a
    brown sauce), and liquids are added "to" it.  Any clearer???
    Sarah

    
    To thicken any cream soup or even to give a little "texture" to 
    clear soups, I throw in some mashed potato buds.  Fast & easy,
    no added fat.
    
    I have some recipes that use roux and also have chopped
    onion as an ingredient.  Example, a broccoli/mushroom/cheese
    bake which is a family favorite or my version of baked 
    macaroni & cheese.  For those,
    I saute the onion in a small amount of fat and then add flour,
    milk etc.  The onion makes it non-lumpy.
    
    ...Shubha
                                           

The fat in the roux also works to prevent lumps (although, I can occasionally 
defy nature on that count!).

If you use flour, uncooked, as a thickener, it will work fine.  Add it to cold 
water, stir till all lumps are gone, then add a little hot liquid to it and 
mix.  It will thicken a little.  Then add this to the pot.  If you find the 
flavor of the starch comes thru, try toasting it in a dry skillet first.  Let 
it cool before adding it to cold water.

If cornstarch, tapioca, or arrowroot powder (oriental markets) is used, I would
not try adding oil at all.  Just add cold water, mix, add to the pot, mix, and
bring to a boil.  Cooking these powders for a long time actually breaks down
their thickening power.  Arrowroot provides twice the thickening power per
calorie as cornstarch.

By the way, "binding" is more along the lines of holding together solids and 
liquids.  E.g., you use bread crumbs and egg as a binder in meatloaf.

Which reminds me, lots of peasant recipes use bread as a thickener.  Soaked
in liquid, then squeezed out and blended in.

Chemically, starches are long chained polymers of glucose molecules with
lots of branches in the chain.  Starch molecules are capable of bonding lots
of water molecules on their surfaces and also capable of lots of cross-
molecule hydrogen bonding when mixed with water (this forms the gooey gels
that all cooks who've used cornstarch have come to know and hate).

When you cook a starch suspension (such as when cooking a sauce or soup
after adding cornstarch or flour), the starch molecules become more highly
branched and cross-linked, and tend to bond more water to them, hence the
thickening phenomenon.

A roux works somewhat differently.  In a roux, you
form a stable suspension where you have small globules of fat molecules
interspersed amongst the water-saturated starch polymer chains.  Fat molecules
are repelled by water and this prevents the globules from coalescing and coming
out of the suspension as a layer of oil at the top of the sauce.  The
structure of the starch molecule chains holds the whole thing together.
It's the same principle as Bernaise and Mayonnaise, only with a roux you're
using starch to keep the suspension together and in Bernaise and Mayonnaise
you're using egg protein.  The whole point is that the fat and fat-soluble
components of the roux are providing a key flavor element to the sauce, but
you need the starch there to prevent the fat from simply forming an unappetizing
layer of grease on the top.

--PSW

Hmmmmm....

I'm not sure which sounds LESS appetizing, "cross-molecule hydrogen bonding",
or "gooey gel"

I've browned flour in a dry frypan. No fat, no liquid. A Revere
stainless skillet is nice for this purpose. Since I usually then use the
browned flour to thicken a gravy, I assume that dry-cooking doesn't
affect the flour's ability to absorb liquid and expand.

Art

    OH!!!!!!
    
    I understand!  Thanks for the chemical analysis.  All now becomes
    clear.
    
    In otherwords, the starch in a roux is there to hold the fat, rather
    than the other way around.  If you don't want the fat at all, no reason
    to use a roux!!!!!!
    
    So from now on, I will simply thicken my soups with plain starch, no
    fat. I feel *much* better!
    
    D!

RE: .12

Yep.  You won't get exactly the same texture or flavor as you would using
a roux, but starch alone works quite well as a thickener.  Chinese soups,
such as hot & sour soup or egg-drop soup, are thickened with a starch/water
mixture.  Roux seems to be a European technology and doesn't occur in the
Chinese repertoire, to the best of my knowledge.

--PSW

re: .4, Carroll

> Where do I get potato starch?

Aside from the instant mashed potatoes that were mentioned in another reply,
I was kinda surprised to learn when I bought my juice extractor this past
year that you could run fresh potatoes through it and use the "potato juice"
directly as a thickener. Makes sense, and since it's naturally "pre-blended"
it should provide a lump free result. They even made a statement as to what
so much potato juice was equivalent to in terms of corn starch. I'll try to
remember to reference it again tonight and post it here.

-Jack

PS. I haven't tried it (using potato juice as a thickeneing agent) yet, so
    I can't comment on how well it works.

    I just bought a bag of potato starch at a chinese grocery in Worcester.
    
    It's unopened if anyone in the MRO area needs it...
    
    Edd

re: my .14

Sorry if I misled anyone - I just checked and no equivalency is stated
in the literature afterall. It just says, "Potato juice may be used in
place of cornstarch or flour as a thickening for gravies and soups."

-Jack

    
    Potato starch is also available by mail-order from Maid of Scandinavia
    
    14 oz. box costs $2.95  (item #46418)
    
    Maid of Scandinavia
    3244 Raleigh Avenue
    Minneapolis, MN  55416
    1-800-328-6722