Stuck Ferment

[Ckilner]

I'm new to AG brewing and I've set myself up with a Braumeister 20L and a MoreBeer SS 7.5 gal conical. After a few mistakes I'm beginning to get to grips with the Braumeister but I still have a problem with stuck ferments (I think).
My last brew had a OG of 14.0 Plato and after a good couple of days fementing, it's stopped at 7.0 Plato. The brew before that started at 10.0 Plato and stopped at 5.0 Plato.
I aerate the wort with a filtered wort aerator for 30 mins before I pitch the yeast starter which I prepare 24 hours earlier and is always very active. I have a heated enclosure for the fermenter which holds the temperature at 20 degs C. I use a Safale S-04 yeast as I'm trying to brew a very light Citra beer using Maris Otter 2 row.
I reckon they should both ferment down to about 3.0ish Plato to get the abv I'm aiming for.
The last time it got stuck I pitched another yeast starter but that had absolutely no effect.

Anyone any ideas what's going wrong please?

 

[Yob]

What temperatures are you mashing at?

 

[Ckilner]

This is for a 15l batch into the keg
[SIZE=12pt]Name[/SIZE][SIZE=12pt] Description Step Temperature Step Time[/SIZE]
[SIZE=12pt]Mash In Add 25.00 l of water and heat to 38.0 C over 0 min 38.0 C 0 min[/SIZE]
[SIZE=12pt]Step 1 Heat to 53.0 C over 4 min 53.0 C 5 min[/SIZE]
[SIZE=12pt]Step 2 Heat to 63.0 C over 10 min 63.0 C 30 min[/SIZE]
[SIZE=12pt]Step 3 Heat to 73.0 C over 10 min 73.0 C 30 min[/SIZE]
[SIZE=12pt]Step 4 Heat to 78.0 C over 4 min 78.0 C 15 min[/SIZE]

 

[Dunkelbrau]

Have you measured with a hydrometer?

I thought that the alcohol changes the reading on refractometers and needs a calculation to ascertain the correct reading.. Unless I'm thinking of something else.. Not sure on the relationship but I thought I read it somewhere..

EDIT:
Here is one calculator relating to brix.. Notice it drops the FG down to like 1.007 when using the same numbers posted above..

http://onebeer.net/refractometer.shtml

 

[Ckilner]

No, it's temperature that affects refractometers. Mine's calibrated to 20 degC

 

[Dunkelbrau]

No, it's temperature that affects refractometers. Mine's calibrated to 20 degC

I thought hydrometers were temp related, and the idea with putting a drop on the plate is that it cools within a few seconds to allow hot wort to measured effectively.

 

[Ckilner]

Yes, I reckon that's right, a few drops only takes a few seconds to cool when put in the refractometer plate so I can measure the gravity of the wort when it's hot.

 

[gap]

No, it's temperature that affects refractometers. Mine's calibrated to 20 degC

Alcohol most certainly affects refractometer readings.

Once fermentation has commenced refractometer readings must be adjusted to account for the alcohol.

Regards

Graeme

 

[Dunkelbrau]

And alcohol is lighter than water, so when read on a refractive scale, it reads higher than it should, I've done a conversion on beersmith and fermenting wort comes out lower than the plato/brix numbers to sg scale. 1.008/1.009 looks to be your current actual gravity.

Do you have a hydrometer to check?

 

[Ckilner]

Just seen Jurt's edit and your comment Gap - interesting point which I hadn't appreciated. Thanks.

 

[Ckilner]

Yes, got a hydrometer. So where I am at the moment, I could use the refractometer reading as the start and then use the hydrometer reading now

 

[Dunkelbrau]

Yeah, that's what I do, since the temp is down at 20ish anyway, it will also allow you to have a taste!

 

[Ckilner]

I thought the good thing about refractometers was that they didn't require a large volume of liguid to do the measurement. So if I have 14 Plato to start then from that moment on, the refractometer reading needs adjusting? How can I use a refractometer from beginning to end?
(BTW, rather pleased that the ferment has almost finished and that things haven't gone wrong again)

 

[Dunkelbrau]

You can use beersmith to adjust for the alcohol, or there are a few calculators around. Best off just leavin it until the krausen is gone for a few days and checking it. The yeast has to clean up after itself to some degree post fermentation.

I like to take a taste at the start (wort) and then a the end, then lots of tastings once its kegged and gassed! I guess the hydrometer tube plays to my will in that regard!

You only need enough liquid for the hydrometer to float though, it doesn't need to be chock full.. What's a hundred mls or so in a 20L batch? ;-)

 

[Ckilner]

Very true, not much volume in the great scheme of things. I was just trying to be a bit too scientific perhaps? With the Morebeer SS fermenter I don't get to see what's happening inside - all I can do is draw off samples and test, so a bit like flying in fog - totally reliant on the instruments. Maybe I should use the refractometer for wort tests and then hydrometer for after fermentation has started. I that the way it's done? Also confused with Brix and Platos. The only refractometer I could buy easily was in Platos but the world seems to be in Brix.
Mostly sussed Beersmith but struggling with the conversion tools but I'm sure I'll get there.

 

[syl]

As others have said:

Refractometer pre and then Hydrometer post ferment is the way to go.

 

[syl]

Bx and Plato are essentially the same.

But for refractometers Plato = 1.04 * Brix.

I do all my measurements in SG and use converrters from Bx/P if required. Because talking in 20 different units ***** me.

 

[CosmicBertie]

Alcohol does indeed skew the refractometer reading. Just use the onebeer link above. I use this all the time. When mashing, I use it for pre/post boil readings, with no adjustment. But once its fermenting, put you numbers into the Onebeer link.

Easy as.

 

[Ckilner]

Thanks everyone. That all makes much more sense now so I'm almost ready to keg .
A slight error in my boil volume calculations means I'll end up with a 5.9% instead of a 4.8% but oh well, I suppose I'll have to cope

 

[mmmyummybeer]

Pity there is no phone app you could get for converting refract readings. Or is there? and I just haven't scene it :unsure: .