Mash night before boil

[gr_baker]

I've done it a few times. I ran off the wort into a sterilised fermenter to keep it overnight. I've had no issues. I've also stored the wort in the boiler overnight (again sterilised) and put the boiler on a timer so it's just about ready to pitch the hops when I've got up in the morning. Again no issues but I'm less happy about this as my boiler lid is not a tight fit.

I've read that you'd get a lower FG but I can't see how this would happen. The theory seems to be that the enzymes responsible for starch conversion will still be active in the wort until the boil and so by keeping the wort overnight you're effectively doing a multi hour mash and that results in a lot of short chain sugars which ferment into alcohol readily giving more alcohol but less flavour.

I've tested my wort using iodine and starch conversion seems to be complete after 30 minutes. So there's no more starch for the enzymes to work on after 30 minutes, unless the sugars produced can be further broken down I can't see how the longer mash would affect things. Perhaps someone who knows more brewing biochemistry than me reading this can explain?

[Mr. Dripping]

The easiest way to describe it is the chopping logs analogy.
Given 2 hours you can chop the tree down in to several big bits. Consider this bit to be the initial conversion of starch to sugars and you will get a negative iodine test.
Give the guy with the axe 8 or 9 hours and he is able to reduce the big logs in to many more smaller logs......i.e. long chain sugars that are not so fermentable are broken down to shorter chain ones that are.

[gr_baker]

Right I see the analogy. I thought that the only two important enzymes in the mash at 60C+ were alpha and beta amylase and that these converted starch to maltose and glucose. What is converting the maltose to glucose in the extended mash?

[mshergold]

I started mashing one day, running off into a fermenting bin and boiling the next day so I could still brew in the winter (I boil outside) and have never noticed any difference. My palette probably isn't as refined as some though. I have to say, it makes brewing a lot more enjoyable than getting everything done in one day.