Three-batch stratification in tank?

[starbro]

We brew 20bbl batches and we have a 60bbl fermenter that we just brewed 3 batches into for the first time last month. All batches were in the fermenter within 36 hours and O2 and yeast were only added in the first 12 hours, etc.

Since we only have a 20bbl brite tank, I could only filter one batch at a time and it took a week to empty the tank due to scheduling issues and having the filter go down for repairs for a day. First batch was great, second batch was good, too. Filtered the third batch today and it was a butter-bomb!

Is it possible the batches may have actually stratified in the tank? A possible theory is that since we rack off near the cone of the tank, the first filtered batch was at the very bottom, 2nd batch at the middle, and 3rd bad batch was at the top. Is it possible the that there may not have been enough circulation in the tank so that the very top may not have fermented as completely as the beer towards the middle and bottom? Off the sample port (about 1/3 up from bottom of tank) we had a terminal gravity of 1.0185, and we had that reading for several days before finally crashing. I took a reading of a filtered sample of the 3rd batch and it is actually 1.022.

The tank has 3 glycol jackets and the temp probe is at about 1/3 up the tank. Fermentation temps were usual and final crashing seemed to go fine as well.

We checked bottled samples from the first two batches to see if it was an infection issue on the tank, but they're fine.

Anyone ever come across this sort of thing?

[chaser]

It's definitely possible and I've seen way to much beer dumped because of it. Our issue was Acetaldehyde, not diacetyl, but same principal of stratification in the tank. The easy/expensive fix is upping the HP of your k/o pump. Eventually we did that. It was simply undersized for the length of the draw to newer tanks, which is where all the issues were (placed further away from the brew-house). The cheap fix, which for the most part eliminated our problem was flipping the racking arm up to about 10 o'clock, and then knocking out the 2nd, 3rd, and 4th brews through the racking arm. That mixes the wort in the tank up better so stratification isn't an issue. Double valve it so you canm do it sanitarily. We also started to pitch yeast on the first and third k/o rather than all in the first. Like I said, we only had issues in tanks that were far away from the brewhouse, so I believe the underlying issue was an undersized k/o pump. Also check into your yeast health, and whether you are over-oxygenating, under-oxygenating, giving to many nutrients, etc. I also spent alot of time checking the yeast count at every k/o, the DO levels, etc. to make sure everything was looking good. Hope that helps.

edit: also look at your yeast strain. it may be floccing out of the top third of the tank too quickly to re-absorb the diacetyl, but has enough contact time with the rest of the tank to have no issues.

[lhall]

I remember a talk at a CBC a while back about multiple batches, by Michael Lewis at UC Davis. His recommendation was get all batches into the tank within no more than 12 hours total.

[Sauce]

hmmm......when you filter to you run a ballast/balance line between tanks?

Just thinking if you dont and you let air into your fermenter and it sat for a day or two that might be how the diacytal developed.

[South County]

hmmm......when you filter to you run a ballast/balance line between tanks?

Just thinking if you dont and you let air into your fermenter and it sat for a day or two that might be how the diacytal developed.

I would imagine they were adding makeup volume with co2.

Another issue/answer may be that once the fermentation had finished the yeast dropped before the upper one third had sufficient contact time to re-up and diacetyl precursors.

Places to start:

1: Over subsequent yeast harvest you may have inadvertently put selective pressure on the strain and harvested early floc cells. Start with a fresh strain and run another 60 bbl batch, test the results, also test gravities as your emptying the tanks, but at only 60 bbls, stratification issues during primary shouldn't be an issue.

2: If the yeast your using is a highly flocculant yeast you may need to rouse it during your d-rest.

In the end multiple fills into 400 bbl plus tanks over 24-36 hour periods is common place. So my guess is that you did not have enough contact time with the yeast during your d-rest for a better portion of the beer in the tank.

[starbro]

Thanks for all the ideas.

The yeast health issue may be the right direction, as all we had was 10th gen yeast available, which is as far as we usually take it. All in the timing sometimes. Would we simply re-rouse the yeast during diac rest with a shot of CO2 up the cone?

We do pressurize tanks during filtering with CO2 and let it balance out between the ferm and BBT. We did have about 4-5 days between the 2nd filter and the 3rd though. Plenty of time for something to go wrong. Now that we're monitoring each batch, I'm not too happy with how the 2nd batch is turning out either, definitely some diac and touch of acetaldehyde, which were definitely not present at time of filtering.

Also, there's no way we're going to be able to get all 3 batches in at 12 hours or under. For a while up until this point we were doing 2 batches into the tank in 24 hours time and never had any problems with it.

[gitchegumee]

I think stratification is an anomaly (unless you have some unusual tank geometry). With the degree of agitation that an active ferment has, coupled with the degree of agitation that cooling via side jackets has, stratification would be difficult to achieve. Just far too much forced mixing going on. I've heard Michael Lewis lecture on the 12 hour rule. I totally, and respectfully disagree. Along with the many other brewers who have heard him and still make great beers by adding wort 24 hours or more after the initial pitch. Don't know why he insists on 12 hours when there are so many folks who show that it can be done to great effect. Anyway, you mentioned that the first two bottled batches showed no sign of infection. That makes sense--they tasted right. Is it possible that you've contaminated the third batch somehow? The batch that tasted of diacetyl should be the one that you run a micro examination on. Hope you get it figured out. And I wouldn't worry about your brewing protocol too much. 36 hours is not unreasonable. Especially at lower temperatures where the wort has not fully attenuated.