BIAB - Constantly false OG Readings with trub in suspension

[Miraculix]

Greetings fellow BIAB homebrewers,

I wanted to point something out, which I brought up before, but now have been able to validate via multiple datapoints and I would like to encourage you to check it for yourself so that we can find out how big the error is on everage.

As we all know, the typical BIAB setup results in cloudy wort and more trub making it into the fermenter than other systems, but we are good with it.

This led me to check, wether or not this suspended trub has an effect on gravity readings, and it looks like it does!

I brewed a blond ale yesterday, chilled the sample to room temperature, sample was cloudy, took the reading, OG = 1,042.

I let it settle over night, quite a layer of trub on the bottom of the sample cylinder, made sure that there was no trub on the hydrometer itself, pushing it down, the sample was now much clearer, new reading OG=1.045. The temperature was the same.

I´ve had this before and the error was as big as 0.005 which is quite a lot for me with my lower abv. beers.

So it looks like with a lot of trub in suspension, the reading is actually a bit too low. Without the trub, the reading is higher.

Can you guys validate this with your system?

Cheers!

M

 

[wstumper]

My experience, although by no means extensive, is that there is a change. To what degree, I don't recall since it wasn't worth it to keep records. Mainly I've noticed this when drawing a sample from what's left in the fermentor after transferring to a keg or bottle bucket. Obviously I let the beer and hydrometer settle for a few hours. It may also be that a little bit of fermentation CO2 is released after sitting in a hydro cylinder for several hours. I generally sample before transferring unless I forget until it's too late!

I'd suspect there are other factors that could explain the change. I use a hop spider to contain hop particles. I "over pitch" yeast since I brew 3 gallons -- haven't figured out to save 25% to 33% of a liquid yeast pack when doing 3 gal batches! Plus I do a fine crush at .025 for 5-6 lbs (when the cheap mill works and I don't want to spend 30 minutes even with a drill.) These 3 points assuredly effect trub quantities in my beer although I am careful about siphoning from boil to fermentor to keg or bottle bucket to avoid transferring wort and beer.

One would have to control and account for all the variables when comparing other brewers and even different BIAB processes.

 

[Miraculix]

Yes, you are right.

For me the question is not so much about the exact number, but if that number is high enough to be necessary to be accounted for or not. If it is just +-0.001... mehh... not worth the look. But if it goes to 0.003 or above, it is actually quite a thing for me to have a look at. If i´m doing a 1.04 beer or a 1.045 is quite a difference, both in abv as well as in hop utilisation in the boil.

 

[DBhomebrew]

Over the last half dozen or so batches, I've noticed the opposite trend. The refractometer sample pulled at flameout has been invariably a few points higher than the very clear sample I take the next morning. Both samples are from just stirred wort and measured at room temp.

I use a water bath to cool down to about 100*F then put the kettle in the fermentation chamber overnight to chill the rest of the way to a few degrees below pitch temp before transferring. At this point, the wort is very clear.

I take quite a bit of data during my brew day including measuring various volumes to the nearest mm of height in the kettle, which works out to the nearest oz or so. Volumes in my computations are adjusted for temp. Combined with a simultaneous SG sample, I can track the accuracy of my numbers through the day. Grav Pts * Vol should provide the same answer at pre-boil and post-. Not so, post-boil I get an inflated number. Chilled and settled the next morning, I get the answer I'm expecting. I'm learning to disregard the post-boil sample. My pre-boil sample matches the sample going into the fermenter and that's what I need to adjust IBUs to keep the recipe's BU:GU.

Note, I'm no scientist and my kitchen is no lab. I'm just a curious amateur brewer looking at trends, ironing out anomalies.

 

[JohnnyO']

The experiment that I would do to verify this hypothesis is:

Take one large sample (enough to do two separate hydrometer readings) with much trub in suspension. Let it all settle. Decant a volume of just liquid and measure. Shake up the remainder and measure.

 

[Miraculix]

The experiment that I would do to verify this hypothesis is:

Take one large sample (enough to do two separate hydrometer readings) with much trub in suspension. Let it all settle. Decant a volume of just liquid and measure. Shake up the remainder and measure.

Good idea, next time!

 

[camonick]

As we all know, the typical BIAB setup results in cloudy wort and more trub making it into the fermenter than other systems, but we are good with it.

This led me to check, wether or not this suspended trub has an effect on gravity readings, and it looks like it does!

I brewed a blond ale yesterday, chilled the sample to room temperature, sample was cloudy, took the reading, OG = 1,042.

I let it settle over night, quite a layer of trub on the bottom of the sample cylinder, made sure that there was no trub on the hydrometer itself, pushing it down, the sample was now much clearer, new reading OG=1.045.

This is just a little off topic, but out of curiosity, do you use any finings in your boil (ie. Whirlfloc)? I have trouble with trub in my pre-boil gravity measurement, but not in my post boil reading. I do use whirlfloc in the boil, cool, then let my wort settle for at least half an hour before racking to my fermenter and taking a hydrometer sample.

I do end up getting some of the trub/whirlfloc into the fermenter at the END of the transfer when I get to the bottom of the kettle. I could probably adjust my water volumes to leave it all behind, but it all compacts with the yeast when fermentation is done, so I don’t get too much heartburn over it.
Sláinte

 

[Miraculix]

This is just a little off topic, but out of curiosity, do you use any finings in your boil (ie. Whirlfloc)? I have trouble with trub in my pre-boil gravity measurement, but not in my post boil reading. I do use whirlfloc in the boil, cool, then let my wort settle for at least half an hour before racking to my fermenter and taking a hydrometer sample.
View attachment 708553
I do end up getting some of the trub/whirlfloc into the fermenter at the END of the transfer when I get to the bottom of the kettle. I could probably adjust my water volumes to leave it all behind, but it all compacts with the yeast when fermentation is done, so I don’t get too much heartburn over it.
Sláinte

No, I don't use anything like whirlfloc or Irish Moss. My boiling pot is actually quite small, so I usually just dump everything into the fermenter, trub and all, wort still piping hot, letting it cool over night. So I literally got the most cloudy wort possible, it is Biab, it is no chill and I don't decant off the sediment from the bottom

Only thing I tried this time is not squeezing the bag to see if there's any difference. Usually I squeeze the ish it off this fellow.

 

[RM-MN]

Hmmm....for about $20 you could get a dual scale refractometer and be able to take readings preboil and post boil without waiting for the sample to cool or worrying about the trub causing off readings. Mine matches the reading I get with a hydrometer and takes only a few drops of wort for the sample.

https://www.amazon.com/Beer-Wort-Wine-Refractometer-Scale/dp/B006GG0TDK

 

[Miraculix]

Hmmm....for about $20 you could get a dual scale refractometer and be able to take readings preboil and post boil without waiting for the sample to cool or worrying about the trub causing off readings. Mine matches the reading I get with a hydrometer and takes only a few drops of wort for the sample.

https://www.amazon.com/Beer-Wort-Wine-Refractometer-Scale/dp/B006GG0TDK

I actually already got one.... But don't ask me where.....

 

[RM-MN]

I actually already got one.... But don't ask me where.....

Well, for about $20 you could get another one.

 

[ba-brewer]

No, I don't use anything like whirlfloc or Irish Moss. My boiling pot is actually quite small, so I usually just dump everything into the fermenter, trub and all, wort still piping hot, letting it cool over night. So I literally got the most cloudy wort possible, it is Biab, it is no chill and I don't decant off the sediment from the bottom

Only thing I tried this time is not squeezing the bag to see if there's any difference. Usually I squeeze the ish it off this fellow.

Sort of off topic, but why do you not use whirfloc and does it eventually clear without it?

I just kegged a beer I forgot to add whirfloc and it looked very milky. The hydro sample was put in the fridge and even after a week it look only slightly clearer.

I normally only use clear wort to ferment by allow it to settle for a while once cooled. My hydro sample normally comes from the left over trub after being filtering thru a reusable coffee cone filter. If you have a coffee filter you could check quickly if it makes a difference instead of waiting over night to clear.