Mystery cooling on our double-batch fermentors

[jscottAT4]

Greetings all,

recently we have noticed our double-batch fermentors being very cold (10-20 below temp setpoint). This usually follows the second batch. Here is a little background on our setup and process

-7bbl brewhouse
-3x 7bbl fermentors, 2x 14bbl, 1x 14bbl brite.
-All tanks share a glycol manifold. They are not daisy-chained, more so in 'parallel'
-Cooling system is controlled by BCS-462 cycling solenoids, using hysteresis temp setpoints

Typical double-batch process is brew 7bbls on Day 1, oxygenate and pitch, brew 2nd batch on Day 2. Usually, there is already activity in the airlock by the 2nd day showing yeast activity. 1st batch gets 02 through stone, 2nd batch does not. We always flow into tanks right around fermentation temp (67ish, +/-10). So on day 1 and day 2, the temperature is already nominal to its desired setpoint.

What we have been noticing is that after we brew and then fill the 2nd batch, our 14bbl tanks are getting colder usually on day 3 or 4, around 10-20 below the setpoint. Initially, we thought this was isolated to only one of our 14bbl tanks thinking it could be a bad solenoid letting some glycol through. Each 14bbl tank is dual-zone glycol, setup where a solenoid controls the feed to supply glycol to cool to one zone which is then looped to feed the other. There are lockout valves on glycol supply and glycol return lines to the manifold. We are fairly positive it is NOT a bad solenoid, as we have previously locked out all valves to isolate glycol flow from tank and it was still sitting around 50 (after flowing in at 70). The tank then warmed up to ferm temps (67) over about 2 days.

Now we have been noticing this more frequently, and it appears to happen to both 14bbl fermentors now. I do not believe this is an issue with our glycol or BCS-462. The issue is only on the 14bbl fermentors - not the 7bbls, or 14bbl brite. And this only happens when we double batch.

Going back to the airlock activity, one thing that seems to happen (preceding the mystery cooling) is a complete blowout when transferring the 2nd batch to the fermentor. What I mean by this is there is already activity in the airlock from fermentation. When the worst starts to flow in, the airlock damn near blows out all liquid in the bucket. It seems to be expelling WAY more gas than the volume being displaced by incoming wort. There is only one down tube on these tank that functions as blow-off and also is the CIP ball. When this gas escapes, you can hear the CIP ball spool up to extremely high RPM as well (picture 5-10PSI in tank and opening the valve). I mention all this detail because I wonder if this is somehow causing our mystery cooling phenomenon. Similar to emptying any sort of compressed gas/air from a tank, the tank gets cooler as the gas expands/escapes. I'm scratching my head, but this is all I can think of. Our other tanks do not have any issues with temperature control, specifically with mystery cooling.

Hopefully I have provided enough info and details here, but please ask any questions you may have and I will do my best to answer

To be fare, I'm not looking to have our brewing process dissected and pissed on, just curious why our tanks are cooling so much for no apparent reason. Any info or insight that anyone has would be greatly appreciated. Thanks for your time!

Cheers,
Jerod

Hi All,

Just an update.

We have made some pretty significant changes to our brewing process. Some of these changes:

-Same day double batching into 14/15BBL, 2 day quad-batching into 30BBL
-Aeration of first half of wort volume ie batch #1 in double batch, #1 & 2 in quad batch. (O2 only stays in solution for 3-6hrs. Here at elevation in CO, its about 4 hrs for us)
-Pitching after #1 of double batch, or between 1 and 2 of quad batch.
-Warmer knockout (75) and warmer FV temp until fermentation starts (any sign of airlock activity)
-MUCH better yeast harvesting/handling/storage/counting/pitching

Through these changes and many more, we pretty much resolved this mystery cooling issue.

However, a few months ago we noticed one of our 14BBL tanks dropping its fermentation temp. It had very active fermentation, as indicated by the airlock. We verified the set temps and temp probe. We were able to isolate to a faulty solenoid valve that controls glycol input to the tank. Noted a slight rumbling on the tank's glycol lines and they were slightly cooler than other static tank lines, so we suspected there was some slight glycol flow through a closed solenoid valve. We replaced the solenoid diaphragm, and the issue seemed to be immediately resolved.

If I had to wager a guess, I would bet our issues before were due to temperature stratification, poor yeast health. The warmer knockout temps, better yeast management, and same-day double batching have yielded some very healthy fermentation, with no further temp issues.


Cheers!

[mmussen]

One thing that comes to mind - before putting your second batch into the fermenter, take a sample of the first batch and see what the temperature is. With a dual zone jacket and the tank only being partially filled it may be that the first batch is much colder than it should be due to the temp probe being above the cooling jacket. That might be where your temp drop is coming from.

[Sauce]

One thing that comes to mind - before putting your second batch into the fermenter, take a sample of the first batch and see what the temperature is. With a dual zone jacket and the tank only being partially filled it may be that the first batch is much colder than it should be due to the temp probe being above the cooling jacket. That might be where your temp drop is coming from.

DING! DING! DING! winner winner chicken dinner!


Nothing more to see here, move along ;-)

[yap]

We have almost exactly the same issue using a nearly identical process. Our temperature probe IS in the wort after day one so the above situation doesn't really apply. If your probe is above the wort, then yeah, that's your problem. If it isn't, here's what we found with our situation.

Batch 1/Day 1 KO at 67° and tank is set at 67°. No problem. Day 2, still at 67° and actively fermenting.

IF we KO Batch 2/Day 2 at 65-66° then we see no issues with tank temperature deviating from 67°.
IF we KO Batch2/Day 2 at 69-70° then when we come in on day 3 the tank may be down as low at 53° even though it's set at 67°.

Here's the best explanation that we can come up with...

As batch 2 goes into the fermenter, it doesn't mix well with batch 1 (at least at first). So once batch 2 displaces Batch 1 your temperature probe will now be reading 70° thus kicking on the jackets. By the time the bottom half of the beer is cooled by the jackets (mostly cone jacket which isn't as efficient IMO) the top half of the fermenter has overshot. By the next day the beer has had enough time to mix due to the activity of the fermentation and the new blended temp is way below your setpoint.


I don't know if this is exactly what happens but it fits our observations. Try to make sure the KO of the second batch is a degree or two below setpoint of the fermenter that way the jackets don't kick on and see if this makes the problem go away...

Unless of course as mentioned above, your probe is above the liquid level on day 1...

[jscottAT4]

We have almost exactly the same issue using a nearly identical process. Our temperature probe IS in the wort after day one so the above situation doesn't really apply. If your probe is above the wort, then yeah, that's your problem. If it isn't, here's what we found with our situation.

Batch 1/Day 1 KO at 67° and tank is set at 67°. No problem. Day 2, still at 67° and actively fermenting.

IF we KO Batch 2/Day 2 at 65-66° then we see no issues with tank temperature deviating from 67°.
IF we KO Batch2/Day 2 at 69-70° then when we come in on day 3 the tank may be down as low at 53° even though it's set at 67°.

Here's the best explanation that we can come up with...

As batch 2 goes into the fermenter, it doesn't mix well with batch 1 (at least at first). So once batch 2 displaces Batch 1 your temperature probe will now be reading 70° thus kicking on the jackets. By the time the bottom half of the beer is cooled by the jackets (mostly cone jacket which isn't as efficient IMO) the top half of the fermenter has overshot. By the next day the beer has had enough time to mix due to the activity of the fermentation and the new blended temp is way below your setpoint.


I don't know if this is exactly what happens but it fits our observations. Try to make sure the KO of the second batch is a degree or two below setpoint of the fermenter that way the jackets don't kick on and see if this makes the problem go away...

Unless of course as mentioned above, your probe is above the liquid level on day 1...

This explanation makes the most sense. I can tell you the temp probe is well in the liquid level after the 1st batch goes in. Basically, the tank is already reading the correct ferm temp after both brew sessions. We monitor or wort temp coming from HX feeding the tank as well as tank temp during knockout.

These tanks do only have 1 thermowell and 2 glycol zones. In fact, on our 14bbl Brite, 1 temp probe controls 2 solenoids (one for each glycol zone).

I guess we could try flowing in colder on Batch #2 to ensure the glycol doesn't kick in. We're double batching out cream stout today/tomorrow, so I'll have more observations to report back on. Thanks all!

Cheers,
Jerod

[soia1138]

We have temp controllers and solenoids to independently control each zone for our 15bbls. Also brewing on a 7bbl bh, if we are double batching over two days then only the lower jacket is turned on until the tank is full.

[jscottAT4]

DING! DING! DING! winner winner chicken dinner!


Nothing more to see here, move along ;-)

Thanks, but Nope

The thermowell is definitely covered. I know this because it is same height as sample port, which we can pull samples out of to double check OG on the first batch. We can also watch the tank temp drop from ambient (80-90ish) to 67ish once liquid level hits temp probe. The level is high enough, and both batch temps are correct.

[jscottAT4]

Also worth noting that tank cooling/glycol is NOT active during knockout as all glycol flow is directed from tank manifold through HX instead.

[jscottAT4]

We have temp controllers and solenoids to independently control each zone for our 15bbls. Also brewing on a 7bbl bh, if we are double batching over two days then only the lower jacket is turned on until the tank is full.

In our setup, only the 14bbl Brite is broken into 2 separate zones like this. After batch#1, glycol never kicks on as the knockout temp was already a few degrees within tank setpoint. We can watch the BCS to see when those outputs are active, and they are not.

[Sauce]

Thanks, but Nope

The thermowell is definitely covered. I know this because it is same height as sample port, which we can pull samples out of to double check OG on the first batch. We can also watch the tank temp drop from ambient (80-90ish) to 67ish once liquid level hits temp probe. The level is high enough, and both batch temps are correct.

Heh...I knew right after I posted that I would eat that post ;-) Oh well, early morning caffeine induced shoot from the hipness, my apologies

[mmussen]

Thanks, but Nope

The thermowell is definitely covered. I know this because it is same height as sample port, which we can pull samples out of to double check OG on the first batch. We can also watch the tank temp drop from ambient (80-90ish) to 67ish once liquid level hits temp probe. The level is high enough, and both batch temps are correct.

Just to point this out. The thermowell being covered does not mean you don't have temperature stratification in the tank. As the liquid cools it becomes more dense and sinks, and most dual zone tanks I've worked with have a gap between the cone jacket and the sidewall jacket where the sample port and the thermowell are. You most certainly can get temperature stratification in that situation, even during the start of fermentation. I would recommend pulling a sample from the racking arm or bottom of the cone and checking the temp just to be sure.

[jscottAT4]

Thanks all for the input and ideas. I will be bale to try some of this and hopefully know more tomorrow during turn 2. I'll keep everyone posted. Thanks again!


Cheers,
Jerod

[jscottAT4]

We have since done our double batch and had no issues with extreme unexplained temperature drops.

However we did a few things different:
-Did not pitch until 2nd batch on day 2
-Knockout was about 4 less than ferm temp.
-Setpoint was set 2 above ferm temp so as to not activate cooling.
-O2 applied to 1/2 cast-out volume for both turns

My guess would be the knockout temp into the tank causes the issue. Based on the majority of your input, i think there is temp stratification. Going intentionally a few degrees lower than setpoint vs at or above to ensure to glycol flow. We're also going to try flowing through downtube 90deg to right with 2nd turn to help mix total volume.

Thanks all for your input!

[barleyfreak]

We have since done our double batch and had no issues with extreme unexplained temperature drops.

However we did a few things different:
-Did not pitch until 2nd batch on day 2
-Knockout was about 4 less than ferm temp.
-Setpoint was set 2 above ferm temp so as to not activate cooling.
-O2 applied to 1/2 cast-out volume for both turns

My guess would be the knockout temp into the tank causes the issue. Based on the majority of your input, i think there is temp stratification. Going intentionally a few degrees lower than setpoint vs at or above to ensure to glycol flow. We're also going to try flowing through downtube 90deg to right with 2nd turn to help mix total volume.

Thanks all for your input!

Bumping an old thread because I will soon be double batching into 14bbls over 2-day span. I may not have the ability to have the 2nd batch come in a few degrees lower than batch 1 due to summer city water temps so it does seem like knocking out #2 by pumping into the racking arm pointed at a 45 degree angle upwards would create some pretty good mixing. Anyone do this?

[soia1138]

Bumping an old thread because I will soon be double batching into 14bbls over 2-day span. I may not have the ability to have the 2nd batch come in a few degrees lower than batch 1 due to summer city water temps so it does seem like knocking out #2 by pumping into the racking arm pointed at a 45 degree angle upwards would create some pretty good mixing. Anyone do this?

I can offer up this experience as we have been both double and quadruple batching for a few years now. I knockout through the racking arm as you describe regardless. It has some benefits for mixing and I can push yeast from a brink in through the bottom while the knockout is in progress. The over-cooling issue from what I can tell is mostly due to lack of fermentation activity. If you knockout one batch and its warmer than the set temp, those jackets kick on and there is no activity going on. The wort cools but the temp probes don't react that instantly, and you have no heat being generated by an active fermentation to work against the cooling power. Just like if you heat water in the kettle to a set temp, the burner will shut off at the set temp but you wind up a few degrees over your set. If you want your fermentation held at 68F the knockout at 66F to ensure that jacket will not turn on until there is actual activity causing the temperature increase. I've never had an active half batch over-cool and we always pitch the full pitch on day one.