Two related yeast questions

[Botch]

I've been jumping around on this forum for a few weeks now, and still haven't found the answer to these two questions so I'll ask them here:
1.  What, exactly, does yeast eat?  All these years I thought you added sugar (or honey, molasses, agave nectar, etc) to a dough for the yeast to eat, and once all the sugar was consumed the dough stopped rising.  However, I've seen dough recipes here that don't include any sugar whatsoever, in fact I tried one yesterday (put one doughball in the frig and left the other out on the counter, the counter ball rose beautifully in a couple hours; i used Caputo "00" and IDY).  So, what is the yeast eating?
2.  What is different about an "Emergency" dough (use within four hours) versus an overnight-in-the-frig dough?  I've read thru the "Emergency Dough" stickie on the General forum, but it isn't really explained what the actual difference(s) are.  The dough I made yesterday was not an emergency recipe, yet I could've easily made a pizza with the doughball after four hours or so. 
 
This has probably been explained somewhere but I couldn't find it, sorry if its an old question...    Thanks! 

[Pete-zza]

Botch,

Sugar, typically table sugar, is not an essential ingredient for pizza dough. There are enzymes in the flour that act on damaged starch to produce sugar in a form usable as food by the yeast. Yeast can only feed on simple sugars. More complex sugars have to be broken down into simple sugars before the yeast can use them. Some forms of sugars like honey, maple syrup, etc., already have simple sugars as components, and those simple sugars can be used by the yeast more quickly (although at different rates usually). To get a better feel for how sugars are used to feed the yeast, you will perhaps want to read the material at http://www.theartisan.net/dough_development.htm ("Sugar Transformations").

The main difference between emergency doughs and other doughs is that emergency doughs typically use a lot more yeast and a higher water temperature. Usually both of these variables are implemented but it is also possible to use just more yeast or warmer water. Room temperature will also be a factor (a dough will rise faster in a hot room than a cold room).

Peter

[Botch]

Thanks Peter!