lilian:
my question is about suger in the dough which suger the yeast prefer to consume natural suger from the flour or added table suger or other suger just your thoughts on that please
lilian,
As the excerpt below from the Yeast Treatise at
theartisan.net demonstrates, yeast, at least in the context of a dough, seems perfectly content to feast off of the free simple sugars and the more complex sugars that are broken down by enzymatic activity into simple sugars during the process of fermentation. Of course, it is possible to add other forms of sugar to a dough, such as sucrose (table sugar), honey, molasses, brown sugar, corn syrup, barley malt syrup (a complex sugar), or even maple syrup, but the question that has to be answered is what is the purpose for doing so? Is it to prolong the usable life of the dough, or is it to add sweetness or flavor to the finished crust, or is it to get increased crust coloration, or is it to alter the rheological (flow) aspects of the dough, or is it to get increased tenderness in the finished crust, or is it to add trace amounts of minerals as yeast nutrients, or is it to alter the rate of fermentation based on the different rates at which yeast metabolizes different forms of sugar (e.g., the fermentation rates for sucrose, fructose and glucose are vastly different)? It can become a difficult balancing act requiring a lot of experimentation to get all of the dough and final crust characteristics you are looking for by altering the sugar component of the dough. As a simple example, consider the natural sugar composition of honey, molasses and maple syrup:
Honey: 38% fructose, 31% glucose, 1% sucrose, 17% water, 13% other
Molasses: 29% sucrose, 13% fructose, 12% glucose, 22% water, 24% other
Maple syrup: 65% sucrose, 0.6% glucose, 0.6% fructose
As you can see, maple syrup comes closest to sucrose (but with a higher water component). You don’t also want to use too much honey because of the high fructose component. And, so on.
You might also be interested in the recent article on sugar by Tom Lehmann, at
http://www.pmq.com/mag/20071112/article … ry=lehmann.
Here is the
theartisan.net excerpt mentioned above:
Sugar Transformations (Rosada)
Simple sugars: The main simple sugars, glucose and fructose, represent about 0.5% of the flour. Yeast can directly assimilate them by penetration of the cell membrane. Simple sugars are transformed into alcohol and carbon dioxide by zymase, an enzyme naturally present in yeast cells. Because of this easy absorption, these sugars are the first ones used in the fermentation process. Their consumption takes place during the first 30 minutes or so at the beginning of the fermentation process.
Complex sugars: The two main types naturally present in flour, saccharose and maltose, represent approximately 1% of the flour. Because of their complex composition, these sugars will be used later on in the fermentation process. The lapse of approximately 30 minutes at the beginning of the fermentation period is necessary to achieve their enzymatic transformation into simple sugars. The enzymes involved are saccharase, which transforms saccharose into glucose and fructose, and maltase, which transforms maltose into glucose.
Very Complex sugars: The main very complex sugar is starch, which represents about 70% of the flour content. Two types of starch are found in flour: amylose and amylopectin. Amylose is degraded by the enzyme beta amylase into maltose, and in turn the maltose will be degraded into glucose by the maltase enzyme. Amylopectin is degraded by the alpha amylase enzyme into dextrin, after which the dextrin is degraded by the beta amylase into maltose. This maltose will them be degraded by the maltase into glucose.
The simple sugar, glucose, obtained during these transformations is used by the yeast to generate carbon dioxide and alcohol. During the fermentation process, most of the starches used are the ones damaged during the milling process. Because the particles are damaged, they can easily absorb water during the dough making process. This water contact triggers the enzymatic activity. A non-damaged particle of starch will only retain water at its periphery and not inside the particle itself.
