bazookazilla wrote:dstar26t wrote:The yeast will ferment simple sugars first then switch gears and start working on more complex sugars. The sooner you add the simple sugar once vigorous fermentation has started, the better, IMO. You want to feed the yeast the syrup before all have switched to maltose fermentation. Glucose (simple sugar) is just ~10% of the sugar in wort.
are you sure about this? I've always been told the opposite.
Just askin'

dstar26t wrote:This is the first reference I could find. Scroll down to "Fermentation".
Nate
You read it right that they consume simple sugars first, but drew the wrong conclusion from it. Generally, it will be better to get them metabolizing the complex sugars, then feed simple sugars late. If an abundance of simple sugars are available from the start (granted, yours is likely lower than the level at which it would cause stuck fermentation problems), yeast will focus on breaking down the simple stuff, and not produce the enzymes for more complex sugars. However, if they are fed maltose, they will produce enzymes for that from the start, but still be able to feed on simple monosaccharides, as all that needs to be done to break down glucose is transport it into the cell and go. Maltose is broken down into glucose by the maltase enzyme, so cells will ALWAYS have the enzymes present to break down glucose, but we would predict that the genes for producing maltase would only be activated when maltose is present.
In other words, they can still downshift to be able to do the simple stuff, but if you get them stuck in 1st gear, they won't be able to shift up to take care of maltose and will stall.
From the BYO article - "In fact, it is known that high levels of glucose and fructose in a wort (e.g. >15–20%) will inhibit the fermentation of maltose. This repressive behavior is probably a common cause of stuck fermentations in worts containing a lot of refined sugars — the yeast have fermented the monosaccharides and then quit, leaving more than half of the total sugars unfermented."