Fundamental question regarding mash temp and fermentability

[william_shakes_beer]

The following are generally accepted as fact:

1. Mash high (155F) and you get a less fermentable wort with more body and mouth feel.

2. Mash low (145F) and you get a highly fermentable wort with higher attenuation and a thinner body

What happens if I do an overnight mash, which is high for the first hour or so and then looses 50 degrees over 8 hours? Do the less fermentable sugars formed during the initial mash get converted to more fermentable sugars as the low temp enzymes become active, or is it a matter of once an enzyme has converted a starch molecule to a sugar molecule, its not effected by enzyme activity any further? I did an overnight mash a couple weeks ago purely to shorten my brew day and would like to have the mental tools to analyze any differences I may notice when it comes to the glass.

 

[billl]

Not exactly. The 2 enzymes in play are alpha and beta amylase. Beta carves off one simple sugar at a time and is active at lower temps. Alpha cuts a starch chain where it happens to land in the chain - either 1 simple sugar or a longer sugar - just luck of the draw. Alpha is most active at higher temps. Both will keep chomping away as long as there is starch or larger sugars available.

The flip side is that both enzymes start to denature quickly as you move them above their favorite temps. So, if you start at the high temp and drift slowly down, most of the Beta denatures before you get to its active range. The alpha will keep working, but the lower the temp goes, the slower it will go. In your setup, you are loosing 6 degrees per hour. After 2 hours, you would be in a range where alpha isn't doing much of anything. Then, over the next 6 hours, you drift over the danger zone of temps where any bacteria that survived the 155 mash could start to grow.

A 2 hour mash is obviously still long by "normal" standards, but that has to be balanced against the high starting temp. Please post a follow with your impressions.

 

[cluckk]

Is there a reason you would want, or need, to do an overnight mash? If you are looking for greater conversion, you can only convert so far--once you have full conversion you are done. Letting it sit longer doesn't help anything. There seems to be a thought among many homebrewers that if a little is good then a lot must be better. If 30 IBUs are good 120 IBUs must be better; if an hour mashing is good 8 hours must be better; if an hour boil is good, three hours must be better. It just doesn't work that way. You are dealing with a fine balance of enzymes, starches and sugars and then in fermentation with living creatures. Each has their preferred environment and going outside of these does nothing good for the finished product. I've heard of people letting a mash sit overnight but not for more conversion--it was simply because of their schedule. They kept the temps above bacterial stages and simply let it sit and denature until the next day when they could boil and finish.

I regularly brew batches using 20-28 lbs of grain and never have to mash longer than 75 minutes--rarely over 60 minutes.

 

[bobbrews]

Everything you need to know right here:

 

[william_shakes_beer]

I did the overnight mash simply to shorten the follow-on brew day. I have no intentionof leaving the stove on all night to maqintain temps. From the posts above it seems like this is not a good practice. Thanks for the input.

 

[mblanks2]

subscribed

 

[hoppus]

I've not done an overnight mash before but the couple times when I've had to leave a mash for 4-6 hours, I ended up with a very thin beer. These were both high gravity stouts so this was undesirable, for my tastes at least.

 

[william_shakes_beer]

Not exactly. The 2 enzymes in play are alpha and beta amylase. Beta carves off one simple sugar at a time and is active at lower temps. Alpha cuts a starch chain where it happens to land in the chain - either 1 simple sugar or a longer sugar - just luck of the draw. Alpha is most active at higher temps. Both will keep chomping away as long as there is starch or larger sugars available.

The flip side is that both enzymes start to denature quickly as you move them above their favorite temps. So, if you start at the high temp and drift slowly down, most of the Beta denatures before you get to its active range. The alpha will keep working, but the lower the temp goes, the slower it will go. In your setup, you are loosing 6 degrees per hour. After 2 hours, you would be in a range where alpha isn't doing much of anything. Then, over the next 6 hours, you drift over the danger zone of temps where any bacteria that survived the 155 mash could start to grow.

A 2 hour mash is obviously still long by "normal" standards, but that has to be balanced against the high starting temp. Please post a follow with your impressions.

Thanks billll, and Bobbybrews. From the information the 2 of you posted, it sounds like neither alpha nor beta amalayse are denatured at my typical mash temp of 155. The alpha amalayse will create long chain sugars, then the beta will come along as the temp drifts lower and convert those to simpler sugars. Kind of like a longer mash at a lower temp. Once I go below the lower temp threshold, all enzymatic activity will stop and my mash becomes fertile ground for whatever bacteria is able to drift in through the lid of my mash tun. Bacteria will be killed in the boil, but by products of bacteria action could remain and alter the taste of the final product. Am I correct in assuming that both alpha amalayse and beta amalayse are fully denatured at 170F? Am I also corrrect in assuming that low temps stop anzyme activity, but do not denature them; IE if the mash cools to a temp that makes them inactive, raising the temp back to the active will range will encourage them to resume their activity?