Fermentation Conundrum

[Monkeyspear]

See what you make of this, because I can't figure it out. I brewed a stout using some opened bags of grains and hops that I wanted to get rid of before I move house (recipe below). The OG was .050. The fermentation started off okay, fairly vigorous. After four days, the airlock activity stopped but I wasn't worried, and left it for another four days at which point I took another reading; the SG was .040. I roused the yeast, and left it for another week - no change in SG. So I made a yeast starter using Wyeast 1056 and dumped in a few days later. A little more activity and then nothing. The SG was still .040.

I guessed I'd made a mistake with the strike temp and gone in way hotter than I thought; both my thermometers seem to be accurate, so I must have misread the one I was using to measure my strike water. To verify, I did an iodine test using diluted wort and it went black immediately, which suggests unfermentable sugars, right? However, I've since reboiled my wort (to kill off any chance of infection), cooled and added a shot of glucoamylase 400, then repitched with a Young's ale yeast. It's been 24 hours and there is no activity and the iodine test still shows signs of starches. pH is 4.1. What's going on? Do the malts I've used possess some unholy, unfermentables that not even glucoamylase can break down, or is there something else at work?

Recipe:
3 kg Weyermann's Chocolate Wheat Malt
1 kg Pale chocolate malt
1 kg Simpsons aromatic malt
28g miscellaneous mixed frozen hops, 12 grams at boiling (60 mins), 12 at 15 mins, the remainder at flameout).
Wyeast 1056 smack pack, made into a starter 48 hours before.

 

[Brew_DD2]

I don't think any of those malts have any diastatic power to convert during a mash. I think you've essentially got dark-coloured starchy water.

 

[MmmBeer]

I don't think any of those malts have any diastatic power to convert during a mash. I think you've essentially got dark-coloured starchy water.

What he said!

 

[Scrattajack]

According to Brewers Friend, that grain bill has a diastatic power of 21 but 30 would be needed to convert it all. The Weyermans Chocolate Malt provides it.

 

[Brew_DD2]

According to Brewers Friend, that grain bill has a diastatic power of 21 but 30 would be needed to convert it all. The Weyermans Chocolate Malt provides it.

It's a roasted malt. Unfortunately it has no diastatic power.

https://www.weyermann.de/eng/bmprodukte_neu.asp?PN=2&idkat=194&umenue=yes&idmenue=37&sprache=2

 

[Monkeyspear]

I don't think any of those malts have any diastatic power to convert during a mash. I think you've essentially got dark-coloured starchy water.

Thanks for the reply. This is what I considered, but wouldn't the glucoamylase convert the starch into fermentable sugars?

 

[Brew_DD2]

Thanks for the reply. This is what I considered, but wouldn't the glucoamylase convert the starch into fermentable sugars?

I know it's certainly used to break down longer-chain sugars into more single sugars. I'm not familiar with the glucoamylase being used as an alternative to a mash though.

 

[Stu's Brews]

Like others have said, your main problem is a lack of diastatic power in your malt. Essentially there wasn't enough enzymes in your mash to convert starch to sugars.

Even for a stout you need to use a healthy amount of base malt, which will give you the diastatic power you need. For reference, this is my malt bill for a stout I did last year:

Maris Otter - 3.6kg
Munich - 400g
Chocolate - 400g
Flaked Oats - 400g
Crystal 150 - 200g
Carafa Special Type III - 100g

As you can see, it was roughly 75% base malt but still ends up at 67EBC with plenty of malt character.

I don't know much about adding glucoamylase as I've never done it but I understand that it can be used during the mash to boost diastatic power. I'd therefore assume it needs to be around mash temperatures for the enzymes to work effectively, what temperature did you add at?

 

[An Ankoù]

The enzyme can be added to the mash or to the wort although it is much more effective at mash temperatures. Here's some stuff from one of the suppliers. Perhaps you need to add a bit more and leave it longer.
It's going to be a funny old beer if it does ferment out. I made a beer from the Durden Park recipe book using 100% brown malt (120 ebc) It's not particularly nice and I won't be making it again. I'd be surprised if your recipe produces anything you'd want to drink, but I could be wrong.

"Glucoamylase 400 can be used to produce low calorie beers. In this application it
can be added directly to the mash vessel at the mashing-in stage. Alternatively, it
can be added to cooled worts after yeast pitching."
https://www.lallemandbrewing.com/docs/products/tds/TDS_ABV_ENZYMES_GLUCOAMYLASE-400_ENG_DIGITAL.pdf

 

[Monkeyspear]

The enzyme can be added to the mash or to the wort although it is much more effective at mash temperatures. Here's some stuff from one of the suppliers. Perhaps you need to add a bit more and leave it longer.
It's going to be a funny old beer if it does ferment out. I made a beer from the Durden Park recipe book using 100% brown malt (120 ebc) It's not particularly nice and I won't be making it again. I'd be surprised if your recipe produces anything you'd want to drink, but I could be wrong.

"Glucoamylase 400 can be used to produce low calorie beers. In this application it
can be added directly to the mash vessel at the mashing-in stage. Alternatively, it
can be added to cooled worts after yeast pitching."
https://www.lallemandbrewing.com/docs/products/tds/TDS_ABV_ENZYMES_GLUCOAMYLASE-400_ENG_DIGITAL.pdf

I added it the cooled wort. I used Brut Force and it suggested adding it to the fermenter, rather than the wort.

It's been sitting now for about three weeks, and actually tastes like a flat, low alcohol porter. I'll concede that fermenting out would probably change the flavour profile somewhat though.

Interestingly I removed a pint yesterday, and added 100g of glucose syrup to experiment with the theory that I could bring the ABV up that way, but there is no yeast activity at all as of this moment. I would have expected something with the wort sitting overnight at around 20 C, so I'm wondering if the wort is somehow hostile to yeast - the pH is rather low at 4.1, but not sure if this is low enough to completely inhibit yeast function.

If anything this has been a sharp lesson for me!

 

[Stu's Brews]

I added it the cooled wort. I used Brut Force and it suggested adding it to the fermenter, rather than the wort.

It's been sitting now for about three weeks, and actually tastes like a flat, low alcohol porter. I'll concede that fermenting out would probably change the flavour profile somewhat though.

Interestingly I removed a pint yesterday, and added 100g of glucose syrup to experiment with the theory that I could bring the ABV up that way, but there is no yeast activity at all as of this moment. I would have expected something with the wort sitting overnight at around 20 C, so I'm wondering if the wort is somehow hostile to yeast - the pH is rather low at 4.1, but not sure if this is low enough to completely inhibit yeast function.

If anything this has been a sharp lesson for me!

Possible that the temperature was a bit too low for the glucoamalyse to work effectively then.

Not sure whether the pH level is a problem or not, this article suggests that a pH below 4.2 would be problematic for yeast activity but I have no other knowledge to confirm or deny whether this is correct.

It is possible that the yeast has gone dormant due to a lack of available sugars for it to ferment, you may need to give it all a good stir to get the yeast back into suspension so it can start to work on the available sugars.

Must admit though that at this point I think I'd be giving up and putting it all down to experience!

 

[Monkeyspear]

Possible that the temperature was a bit too low for the glucoamalyse to work effectively then.

Not sure whether the pH level is a problem or not, this article suggests that a pH below 4.2 would be problematic for yeast activity but I have no other knowledge to confirm or deny whether this is correct.

It is possible that the yeast has gone dormant due to a lack of available sugars for it to ferment, you may need to give it all a good stir to get the yeast back into suspension so it can start to work on the available sugars.

Must admit though that at this point I think I'd be giving up and putting it all down to experience!

From what I remember of enzymes from my undergrad zoology degree (a good few years ago now!) they will still work within a certain range, just at a slower rate; heating up the wort increases enzymatic activity as it increases the rate at which enzymes meet the molecules which they break down, until the wort gets so hot the enzyme denatures.

But yes, definitely at the point now where it will be tossed and chalked up to a learning experience!

 

[Stu's Brews]

From what I remember of enzymes from my undergrad zoology degree (a good few years ago now!) they will still work within a certain range, just at a slower rate; heating up the wort increases enzymatic activity as it increases the rate at which enzymes meet the molecules which they break down, until the wort gets so hot the enzyme denatures.

But yes, definitely at the point now where it will be tossed and chalked up to a learning experience!

Sounds like you probably know more than me about enzymes then!

Hope that the next brew goes a bit smoother!

 

[Monkeyspear]

Update on this for anyone interested. I ended up adding a load of sugar to this brew, raising the SG to 1.070 from .040. I expected the yeast to munch through the sugar and get the SG back down to .040 but, lo and behold, it went down to .020. Seems that the glucoamylase did cleave up the long chain sugars, but this process took a lot longer than 48 hours (I was taking regular readings throughout this period).

I'm now brewing up some base malt (Crisp Vienna and Crisp No19 Maris Otter) to mix with the black brew which, incidentally, doesn't taste that bad by itself. Very nutty with lots of mouthfeel and plenty of coffee and chocolate undertones.