Propagator aeration question

[kippercb]

Hi all. First post here, I'm just putting together my little brewery, first batch of wort expected to flow in about 2 weeks! I've got a 100L propagator and am wondering how best to oxygenate the yeast in the growth phase. I have O2 but I obviously don't want to continuously run pure O2 in the prop. I was looking at clean (oil-free) compressors and they are both expensive and a bit overkill for my tiny prop, then I saw a large(ish) hobbyist aquarium pump for cheap that says it pumps to a depth of 2m, way deeper than the depth of my prop, wondering if this would be a good idea, with an inline 0.45um filter. I've never used a 'real' yeast prop before, but I have made many nano-sized pitches on a DIY prop with a carboy and small aquarium pump through a filter and oxygen stone.

Suggestions welcome!
Stephen
Brouwerij de Kromme Haring, Utrecht NL

[dick murton]

I thought I had some suitable info, but if I have, cannot find it. The concept is fine, but I strongly suspect that the particular pump you are thinking of develops too little pressure to be able to push through the filter itself, before you bubble through the culture. The only way to check this would be to go to a filter supplier such as Pall, Cuno or DomnickHunter (Parker) and give them details of the flow rate and pressure you can supply air at.

Don't forget that ideally, the whole system from filter cartridge / housing through to the injection point needs to be sterilisable. You should also consider a non return valve in the system between the propagator and the filter housing., so nothing runs back into the filter, If the filter is wet, I am absolutely certain you will not be able to clear it with this sort of head pressure.

Though not my preference, (but then I accept I have been used to big brewers capital, not micro brewers capital), you could simply to use sterile, food grade air, without a filter, but having cleaned the dosing line (including NRV) prior to connecting the gas bottle and propagator - without a sterilising filter. When connecting the gas bottle, sterilise with methylate spirits or similar high alcohol content liquid.

[Frank A]

What are your batch volumes and density average going to be? If you have a meter inline to measure the amount of O2 or air pushed into the system you can calculate the appropriate dosing. Air is what we use to build cultures up to pitchable numbers (a simple filter cap on flasks) but we aren't making slurries larger than 15-20L for our little brew lab. Oxygen administered through a steel diffusion stone might be best to ensure a saturation, so long as it's controlled in its release. Nutrient and oxygen requirements will likely vary depending on where the source is coming from - off the bottom of a fermenter, top-cropped, a yeast order, or built up from slants. To start I would recommend sticking with what is working for you at first and get a baseline established.

[scotts]

We're facing the exact same issue as the O.P. We've located sterile filters and housings that will work with the flow we have in mind (1-5L/minute depending on the stage), but it's the air source that we're still trying to figure out. We can buy sterile air from our CO2 supplier, but it's not cheap considering it will be running 24-hours a day during propagations. In the end, I think we'll use air from our air compressor with some coarser filters in front of the sterile filter. At the low flow rate we're talking about, I'm guessing that any moisture and grease will be minimal before it has a chance to blind the sterile filter. We'll soon find out.

As far as what to do with the air once it's filtered - we're going to recirculate the yeast with a peristaltic pump from the bottom to the top of the propagation tank. Just before it comes back into the tank we'll have a steel diffusion stone that will inject the air into the yeast to keep it oxygenated. I've heard that pure O2 can damage or kill yeast, which is why we're sticking with air.

[kippercb]

Hi All, thanks for the advice,
Here's what I'm doing... for what it's worth! I've done 1 batch in the prop and am about to run my second. My lab wasn't up yet so I couldn't count cells for the first, I will count for the second. I got the large aquarium pump that says good to 2m depth, hooked that to the down tube (in through a side port and runs down to the bottom of the cone), pushed air through there with a 0.45um syringe filter inline (no non-return, just hanging the line so that the filter is highest point, indeed they don't push air once wet), no stone on the end just bubbles. Ran a blowoff-style outlet out from the head space. It worked fine actually, bubbled away gently. Again, I couldn't count cells but the harvest looked enormous, based on slurry volume and subsequent fermentation activity I'm certain it was a substantial overpitch. I'm now on the fourth generation of that pitch and it's going great.

The problems with my little system, I can't do proper sterile culturing, can't measure air flow rate, I have a carlsberg flask that I have no way to sterilize, and I'm not doing sterile yeast injections. When the lab is finished I'll be plating out for contaminants but for now I'm just being as careful as I can.
This means:
-If from a plate / slant / glycerol stock, then grow up 20ml -> 200ml -> 2000ml, shaking/stirring flask.
-If from a vial or smack pack just the 2000ml
(Larger volumes here are made with extract powder on homebrew setup, either running boiling wort to vessel or immersion chilling and running off)
-decant supernatant and inoculate 20L in carlsberg, constant aeration through filter
-after 24-36 hours push entire contents (via pump filter) into prop containing 50-100L wort.
-aerate 24-36 hours, (count cells), leave to flocculate, chill with glycol if needed, harvest into brink, (re-count the slurry).

[Yeast]

maybe you've already seen this

http://discussions.probrewer.com/showthread.php?55700-Laboratory-propegation-and-Brewery-propegation-of-yeast-(SOPs)

this is how I would approach it if your prop is a conical vessel

[kippercb]

Hi Yeast, No- somehow I'd missed that! Thanks for bringing it to my attention, and great writeup. I'm doing basically the same in the prop (yes it's conical) but 4x smaller.
Cheers