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Conference turris::cooks

Title:How to Make them Goodies
Notice:Please Don't Start New Notes for Old Topics! Check 5.*
Moderator:FUTURE::DDESMAISONSec.com::winalski
Created:Tue Feb 18 1986
Last Modified:Thu Jun 05 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:4127
Total number of notes:31160

3834.0. "Scum! What, why is it?" by SUBURB::MCDONALDA (Shockwave Rider) Fri Aug 13 1993 06:11

    When making a stock (whether it be meat or vegetable) or even doing
    something like boiling potatoes, scum forms on the surface of the water.
    
    What is this stuff? Why does it form? Are there ways of stopping it
    forming or of reducing the amount that forms?
                                      
    Angus
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3834.1KERNEL::SMITHERSJLiving on the culinary edge....Fri Aug 13 1993 07:334
    Is it starch?  I get that as well - perhaps its the stuff they add 
    to the water.  Scary thought..
    
    
3834.2ENABLE::glantzMike @TAY 227-4299 TP Eng LittletonFri Aug 13 1993 09:2511
I don't know for sure, but would guess that with vegetables, it's
starch and some cellulose, and maybe some unsoluble salts which form
when stuff in the potatoes mixes with dissolved minerals in your water.
It may look ugly, but it's totally harmless.

When you boil meats, the scum is basically protein (from blood, tissue,
etc). Also harmless.

In any case, the main reasons for skimming it off, if it's even
necessary, are (1) to make it look nice, and (2) sometimes contains
bitter tasting stuff, which could subtly affect the flavor of some dishes.
3834.3GEMGRP::PW::WinalskiCareful with that AXP, Eugene!Fri Aug 13 1993 21:3619
I wonder if anybody's ever done a detailed chemical analysis to find out what 
exactly is in soup scum?

Scum from boiling potatoes is mostly starch, partly denatured (read: cooked) 
and oxidized (exposed to air), along with other complex polysaccharides 
(pectins and whatnot), hydrated so that it forms a thin slimy layer.

Soup scum would mainly be low-density lipoproteins and cell coat 
polysaccharides, similarly oxidized, denatured, and polymerized to form a 
sticky layer.

In either case, it forms because of the exposure to air of these substances 
when they float up from the liquid being boiled.  You can't really stop it from 
forming unless you completely seal off the surface of the liquid from the air. 
You can reduce the amount of it by putting a cover over the pot.  That helps 
keep the surface moist so that the drying effect of the air doesn't denature 
things as rapidly.

--PSW
3834.4when you don't want itTNPUBS::STEINHARTBack in the high life againMon Aug 16 1993 10:135
    If you want very clear chicken soup, skim off as much as possible.  If
    you are really ambitious, strain it through cheesecloth in a colander
    when it is done cooking.
    
    Laura
3834.5ENABLE::glantzMike @TAY 227-4299 TP Eng LittletonMon Aug 16 1993 13:172
You can also use put eggshells in to clarify broth, after skimming and
straining. Makes it perfectly clear.
3834.6mom's way.JEREMY::RIVKARivka Calderon,Jerusalem,IsraelTue Aug 17 1993 04:066
    re .4 
     another method for getting clear checken soup - when the soup is
    cold enough put it in the fridge. for 12 hours.You will get a thick
    surface-just use a spoon to peel it off.(we like the taste of "whole"
    chicken soup without the skin-fat taste.)
    r/
3834.7ENABLE::glantzMike @TAY 227-4299 TP Eng LittletonTue Aug 17 1993 09:304
Yes, that's one of the best ways to remove the fat and scum. But it
still leaves small particles at the bottom. That's what straining
and/or egg shells remove, leaving a totally clear broth (which,
honestly, I rarely have a need for).
3834.8egg shells?BAHTAT::WALKER_DDavid WalkerMon Aug 23 1993 09:062
    do you crush the egg shells to a powder before adding them ?
    
3834.9ENABLE::glantzMike @TAY 227-4299 TP Eng LittletonMon Aug 23 1993 09:402
No, they don't have to be broken up at all. Makes it a lot easier to
strain them out, too.