Originally Posted by somedudefromguam
I don't think a longer mash= a more fermentable wort, isn't it the mash temp? I mean if you mash at 158 for an hour versus 30 minutes won't you get the same body(FG) in the end product. And (I too am no expert) if you mash at 158 until a negative starch test, you pretty much have your fermentability and final gravity set in place, you can't then mash for longer while the temperature in the mash drops and expect to get a lower final gravity. True?
Not necessarily. It's important to have an idea of how the two saccharification enzymes work together to make wort sugars out of starch in the grain.
Some beta amylase will still be active at higher temperatures, and add to that the fact that alpha amylase is still working and you'll get more and more fermentable wort.
Let's say you have complete conversion of the starch to sugar in 30 minutes. That means you probably have a lot of long chain sugars, some of which are shorter (more fermentable than others). Neither enzyme can make a sugar longer, but both can cut up the existing long chain sugars FURTHER into smaller and smaller sugars. Therefore, longer mash= more fermentable wort.
Temperature definitely is a major factor, as it tips the balance between one enzyme and the other, but time is another important factor.