Cropping Flow Rate

[NuukBrewer]

What is a ballpark yeast harvest flow rate to avoid tunneling through fermenter yeast cake?

I want to crop my yeast in a controlled and consistent manner. Slowly harvest, to allow yeast in fermenter to slide down the cone, come out in as defined layers as possible, and drop as much yeast from the fermenter as practical.
I assume strain/flocculation characteristics will have a big effect, as well as fermenter geometry and maybe size.
But what is a ballpark cropping rate so I can order an appropriate flow meter?

Details:
40hl cylindroconical fermenters (~65 degree cone angle)
Mostly using US-05 and S-23

[Chaz]

FWIW, This is what "Yeast in the Brewery" by Annemueller says, I happened to be flipping through that section:


The yeast crop from a CCV
When the fermentation takes place in cylindroconical tanks (CCV) the yeast sediments
in the tank cone and can be cropped from it. This is made possible by different factors:
the gravitation, the static pressure of the beer column and the bunging pressure. If
necessary, the sedimentation can be supported by a pump.

Pumping can at the same time help to limit or to maintain constant the flow of the
yeast slurry during collection, provided positive displacement pumps are in use (e.g.
rotating piston, eccentric screw or membrane pumps). It is thus possible to crop the
yeast slowly and within a precise time limit, as it is given enough time to slide down in
the cone (maintaining "intact” the horizontal boundary yeast/beer). In fact, if the time
given to the yeast to slide down is too short, a sort of "funnel" is formed in the yeast
sediment, and mainly beer (instead of the thick yeast slurry) flows through to the outlet.
For this reason, the yeast crop flow should be:
- In a 250 m3 - CCV: < 10–15 hl/h or
- in a 500 m3 - CCV: < 20–30 hl/h.

Maybe my metric cubed is pretty poor but I think those are much bigger tanks.

[NuukBrewer]

Great coincidence that you happened to be passing by that section. Thanks for passing it along.
Those are huge tanks. 1m3 = 10hl, 250m3 is 62.5x the volume of our tanks.

[MikeyB]

All the factors you assume affect cropping surely do, as well as when you do it, and they all interact with each other. The best tool I've found is a programmable peristaltic pump, which will let you go slow and steady. Reasonable flow rates might be in the ballpark of 0.5-2.0lpm. You can set a pump like this up with volume or time limits depending on your controller, and let it run unattended.

[NuukBrewer]

Programming a peristaltic pump to harvest the yeast and being able to "set it and forget it" is a huge benefit.
My concern is the added complexity of CIP. It would require a bypass loop to get enough flow past the pump, which isn't out of the question but nudged me to considering a flow meter and diaphragm valve combo. Reconsidering...

[dick murton]

Those flow rates quoted for the large vessels are very slow, but put that to one side as those figures are irrelevant. Unfortunately, yeast cropping flow rates depend on a few things - cone angle - yours shouldn't be a problem, head pressure - to some extent, as long as the CO2 is kept in solution. The main thing is the yeast consistency at the point of cropping. We had some yeasts that we could crop fast, at almost 100 hl / hr, others that would start at less than 20 hl / hr and later ramp up to about 40 hl / hr - all in 2000 hl cylindroconical vessels. Temperature at the point of cropping make a big difference to yeast consistency, as does how long you leave it before cropping - in general terms, the longer it has to sediment, the higher the consistency and thus slower to crop. Different yeasts also seem to have differing viscosities, even with nominally the same % yeast solids. So, afraid it is a bit of trial and error.

The use of peristaltic or diaphragm pumps is fine, but they are positive displacement pumps so on no account must you put a restriction in the form of a flow control valves of any sort on the outlet side. And you must have a by-pass valve for cleaning as your pipework needs an absolute mi9nimum flow of 1.5 metres (ca. 5ft) / second, and better at 2 metres (ca.7 ft) / second, which you will not be able to achieve through a PD pump. We had great difficulty getting reliable flow meter readings out of pulsing flows from a diaphragm pump, and even the peristaltics gave us problems. You could use a timer for slow sped, and a second timer at slightly higher speed etc. which worked reasonable well (but definitely not perfectly) for us

[gitchegumee]

I've had near-perfect success with small peristaltic pumps in breweries and cideries. Push the hose over a suitable barb/TC fitting, connect to tank bottoms, and let it go. Get a pump with variable speed. A timer is useful, too. These inexpensive pumps allow you to set-and-forget dropping tank bottoms, harvesting yeast, as well as for precision yeast dosing, sulfites, priming sugar, preservatives, flavors, etc. We ran one at high speed to recirculate yeast in a 50 liter brink during propagation. Allows for great sample to count yeast and calculate yeast dose. After calculating your pitch volume, set it for a reasonable dose time during knockout and forget it. When finished, simply remove the hose and run some soapy water through it. Simple to sanitize too. Easy and cheap to change hoses. We used them to acidify sparge water too. A simple, highly effective, and inexpensive tool to improve quality and consistency in breweries and cideries. What is not to love?

Back to the OP, I've found one variable that makes LOTS of difference in slurry collection speed is the surface finish of your cone. If the yeast can't slide, you'll eventually rathole. Mirror finished tanks drop brilliantly clean.

[NuukBrewer]

Yeast slurry harvest flow rate data I have collected:

Fermenter Size (hl)	~40	700	2000	2500	5000
Flow rate (L/min)	0.5-2.0	38	33.3-166.6	16.6-25	33.3-50
Source	MikeyB	G.M.	dick murton	Annemueller	Annemueller

Thanks for all the comments regarding using a peristaltic pump.
My opinion has been swayed by the utility of such equipment.