Low than expected gravity of 1.006

[AlanJones]

Wondered if anyone can explain why my latest BIAB batch has a gravity of 1.006 (after 6 days) instead of the estimated FG of 1.010. I know its an estimate and am not worried as the sample tastes quite nice, just wondered why its happened as never had such a low reading. My process was the same the only difference being that i did the mash the night before and left the wort minus the grains in the pot ready to boil the next day. I guess this is the reason but again just wondered why this has a difference.


Recipe (15L) was:

2.5 Kg Maris Otter
100g wheat
100g crystal
50g biscuit
15g chocolate

mashed at 67 for 60 mins

10g Target @ 60 & 30 min
15g Atlas @ 15 mins
20g Atlas @ 5 mins

yeast safale 05


Thanks
Alan

 

[strange-steve]

What was your OG?
Unless you did a mash out step or cooled the wort the enzymes would have been active for a long time, leading to a more fermentable wort, just like an overnight mash.

 

[peebee]

Wondered if anyone can explain why my latest BIAB batch has a gravity of 1.006 (after 6 days) ...

You've pretty much answered your own question.

Assuming you didn't boil the wort after mashing, or at least didn't raise the temperature above about 75C, your wort will have active enzymes and a medium stuffed full of complex sugars that the enzymes can work on. The enzymes don't just work on starch in the grain but first break the starch down to complex sugars (soluble, so they are there even if you remove the grain), and then break them down to simpler sugars. The yeast is pretty lazy and prefers simple sugars, and might even be unable to ferment many complex sugars.

Balancing the complex and simple sugars is an activity of the brewer. I brewed a pale ale recently that went down to 1.006 but I mashed at 64C to make sure that happened.

And brewing with US-05 just further makes sure that will happen (it's quite a persistent strain).

 

[AlanJones]

thanks for replies, OG was 1.039.

I didnt do a mash out or cool the mash. After removing the grain bag i topped the pot up a bit with some sparge water, put the lid on and left it over night.

 

[MyQul]

What was your OG?
Unless you did a mash out step or cooled the wort the enzymes would have been active for a long time, leading to a more fermentable wort, just like an overnight mash.

This doesnt happen.When I was looking into the pro's and con's of doing an overnight mash it stated that almost of the conversion was done in the first 10-15mins and the rest of the time the mash is just sitting there waiting for you to get on with the lautering, sparging etc. I've done a few overnight mashes and I never got a really low FG. The only thing that happened different was that I got a good efficiency on my lower OG brew but the same efficiency on brews with around 5kg of grain

Edit. This link (forth Q down) explains it better than I can and is what I read when I was first looking into overnight mashing (apologies for my mistake saying the mash is finished after 15 mins. As it says in the link everything is done by 1 1/2 to 2 hours) http://www.brewboard.com/index.php?showtopic=30815

 

[strange-steve]

This doesnt happen.When I was looking into the pro's and con's of doing an overnight mash it stated that almost of the conversion was done in the first 10-15mins and the rest of the time the mash is just sitting there waiting for you to get on with the lautering, sparging etc. I've done a few overnight mashes and I never got a really low FG. The only thing that happened different was that I got a good efficiency on my lower OG brew but the same efficiency on brews with around 5kg of grain

Edit. This link (forth Q down) explains it better than I can and is what I read when I was first looking into overnight mashing (apologies for my mistake saying the mash is finished after 15 mins. As it says in the link everything is done by 1 1/2 to 2 hours) http://www.brewboard.com/index.php?showtopic=30815

It's not something I've ever actually done, but what you say makes sense when you think about it. So it's one of those pieces of conventional brewing knowledge that everyone "knows" but, as is often the case, isn't true.

 

[MyQul]

It's not something I've ever actually done, but what you say makes sense when you think about it. So it's one of those pieces of conventional brewing knowledge that everyone "knows" but, as is often the case, isn't true.

You right there's loads of things in brewing that are taken as given but when actually put to the test don't hold up. I think that is why brulospher is so popular as he put a lot of these 'givens' to the test

 

[peebee]

This doesnt happen. ...

Well "strange-steve" might be for throwing the towel in, but I'm not!

We're only after explaining a few points of gravity (1.010 expected, 1.006 got) and leaving the wort to cool from the moment its first mixed for several hours is going to sway the fermentability towards that end; enzymes don't stop to some timetable, they are rendered less effective as time goes by. People determine this "40-60 minutes before it becomes denatured" (it's the beta-amylase we're concerned with here) on the basis that a "threshold" of x% has denatured. Whatever x% might be; no-ones said.

Add to that a very attenuative yeast like US-05, an SG we now know was only 1.039, and the conclusion you have an FG of 1.006 hardly becomes unexpected.

Right, I'll crawl back into my cave, it was getting rather hot in there anyway. But if you want me to crawl out again you'll know how best to wind me up I'm sure.

 

[MyQul]

Well "strange-steve" might be for throwing the towel in, but I'm not!

We're only after explaining a few points of gravity (1.010 expected, 1.006 got) and leaving the wort to cool from the moment its first mixed for several hours is going to sway the fermentability towards that end; enzymes don't stop to some timetable, they are rendered less effective as time goes by. People determine this "40-60 minutes before it becomes denatured" (it's the beta-amylase we're concerned with here) on the basis that a "threshold" of x% has denatured. Whatever x% might be; no-ones said.

Add to that a very attenuative yeast like US-05, an SG we now know was only 1.039, and the conclusion you have an FG of 1.006 hardly becomes unexpected.

Right, I'll crawl back into my cave, it was getting rather hot in there anyway. But if you want me to crawl out again you'll know how best to wind me up I'm sure.

It could possibly be, as you mention, the attentuation of the yeast, whether it was re-hydrated or not or maybe how aerated the wort was, or fermentation temp as non of these things are mentioned in the OP, not to mention the possibility of bacterial or wild yeast infection- not trying to wind you up or anything :whistle::lol:

 

[peebee]

... not trying to wind you up or anything :whistle::lol:

Hum... first rule in winding folk up is they're not to know they're being wound up. I know you know exactly what I think about the modern trend of blaming everything on "infection". So I've only bothered to open one eye to see this... and I'm closing it again now ... zzz.

 

[MyQul]

Hum... first rule in winding folk up is they're not to know they're being wound up. I know you know exactly what I think about the modern trend of blaming everything on "infection". So I've only bothered to open one eye to see this... and I'm closing it again now ... zzz.

:lol::lol:

In all seriousness the OP hasn't actually given us a lot info to go on. Take pitching rate for example. He says his process was exactly the same but simply mentions he used US-05 for previous brews. Did he use fresh packs of US-05 for each brew he's made or has he, for this brew, re-pitched some slurry and if so how much, did he make a starter, how old was the slurry, etc. I'm sure you know there's loads of factors effecting FG, many of which the OP hasn't mentioned. But all said and done of those factors could be the overnight mash but we haven't ruled out any of the other many factors yet

 

[MickDundee]

Reading the OP, I don't think he did do an overnight mash. Looks like he did the mash, removed the grains then kept the wort warm overnight

 

[dad_of_jon]

Hum... first rule in winding folk up is they're not to know they're being wound up. I know you know exactly what I think about the modern trend of blaming everything on "infection". So I've only bothered to open one eye to see this... and I'm closing it again now ... zzz.

If it tastes good its less likely to be an infection, my fg's have ranged from 1019-1001 none of them were infected so 1.006 is not a disaster. Equally a gushing bottle could be over-priming. it's more likely a combination of wort ferment-ability and yeast used but that's as specific as i'm prepared to get :whistle:

 

[MyQul]

It could be something as simple as a faulty thermometer. @ the OP. Try calibrating your thermometer tom make sure it's accurate

 

[AlanJones]

Used a full fresh pack of yeast (no starter) and no it wasnt an overnight mash, i just did the mash the night before and left it in the pot over night (minus the grains) to save time the next day. Thermometer is quite new and i checked it the first time i used it. Aerated wort and pitched yeast at 20 degrees and fermented at around 15.

 

[peebee]

... and no it wasnt an overnight mash, i just did the mash the night before and left it in the pot over night (minus the grains) to save time the next day. ...

Yes we know. But the enzymes and sugars (even a bit of starch if you happen to suffer from starch hazes) carry over in the liquid so "mashing" continues without the grain. But for how long? That is what we were having the bun fight about.

Anyway... US-05 has a published attenuation (estimated) of 81%. Your SG was 1.039. So an estimated FG might be 1.007. I think you can question where your estimate of 1.010 came from rather than worry about having a FG of 1.006.

 

[Gerryjo]

Just to throw a spanner in the works I have just bottled one of my Christmas brew's and as I went over my notes I remembered I got a jump start the night before on the partial mash as I had mashed the grains,let cool in the pot to 20 degrees and checked gravity at 11.30pm which was 1.035 and this sat covered with the lid overnight.
The following morning at 8.30am as I was preparing I rechecked the gravity and was now 1.040 at 19 degrees.
At the time I didn't pay much attention but this thread is really beginning to interest me regarding this.

Sent from my ALE-L21

 

[peebee]

Just to throw a spanner in the works ...

You haven't really. I think all the antagonists have dropped out because its dawning on them how complex the mechanisms involved are. I know I've been modifying my responses so as to fit with some of the ideas.

We could get all "Chris Peckham" (BBC - Spring Watch) about it and start drawing graphs; but to cover the variables we'd need 3 axis graphs, and when that isn't enough move to 3D graphs, and beyond? And then you'd need the data... na, give up.

Animal enzymes are easier. They evolved to work most effectively at body temperature. So amylase in our spit will convert (more accurately catalyse the conversion) more starch at 37C than at 45C. But 45C doesn't necessarily denature (bust) the enzyme. Plant enzymes on the other hand just keep accelerating the conversion with rising temperature until a temperature at which most of the enzyme denatures. Brewers use this feature to determine the best temperature to arrive quickly at a suitable outcome. The "best" temperature being a balance between what's best for the Alpha group of malt amylases (break starch into complex sugars) and what's best for the Beta group (break complex sugars into simple ones). And the balance can get more complicated by "stepped" mashing. Remember these different methods of mashing were worked out when no-one had a clue what an enzyme was.

And then there's the yeast: Some just digest their way through only the simple sugars (low attenuation), some have a crack at the more complex sugars (high attenuation). Published attenuation figures are based on a "representative" sample of wort; whatever that might be.

If anyone's fallen asleep reading this, that's probably the best policy. I need to go back to bed now.