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Medical Forum / General / Laboratory / April 2007seperating yeast from wort
Hope this group can help or direct me to the correct one. I grown yeast as part of my beer homebrewing process. I start with a 100ml yeast culture and gradually step up the cell count by adding sterilized wort (unfermented beer) until I have 2000ml of over a 4 day period. Then I chill the yeast & wort mixture overnight and the yeast drops out of solution. In a 2000ml Erlenmeyer flask I end up with around an inch or so of yeast in the flask. In trying to decant the spent wort off the top of the yeast, as gently as I try I still get yeast back into solution loosing some of my effort. Is there a better way to get the wort off the top of the yeast without disturbing the yeast cake in the bottom of the flask? In the homebrewing newsgroup everybody pretty much does the same as I've described and accepts that as a loss. Please excuse my ignorance if I posted to the wrong group for advice. >Hope this group can help or direct me to the correct one. I grown yeast as >part of my beer homebrewing process. I start with a 100ml yeast culture and [quoted text clipped - 6 lines] >a better way to get the wort off the top of the yeast without disturbing the >yeast cake in the bottom of the flask? Don't know about making beer, but here are some things people would do in the lab for such a situation... centrifuge; makes the yeast pellet more solid. filter, rather than just decant. Or, and something that might be practical for you... The geometry is against you. You have a very large surface area of liquid over yeast. It is hard to not disturb it. So... decant off what you can, with "absolutely no" carry over of yeast. Then stop. Now decant off some more into a fresh -- and smaller -- vessel, a vessel with a small diameter. (Smaller the better, so long as it works.) This time try to get all the bulk liquid, but some yeast will come along. Now let this settle, and decant off the fluid layer. The key is to do two separation steps, and improving the geometry (lowering the surface area) the second time. I doubt it is worth it, but you could try it and explore. bob >In the homebrewing newsgroup >everybody pretty much does the same as I've described and accepts that as a >loss. >Please excuse my ignorance if I posted to the wrong group for advice. Thanks Bob, one of the critical elements in brewing is keeping the yeast from getting infected before it is pitched into the wort. The goal is having the little critters at a high enough colony count to begin a rapid fermentation when pitched into the wort. Infections during the yeast stepping-up phase will create off-flavors in the finished beer. So every transfer to another vessel runs the risk of infection. My current practice when stepping up the yeast growth is to flame the lips of both flasks add fresh wort briskly, holding my breath during the transfer and minimizing the time the airlock is off the starter flask. The yeast starter then goes back on the stir plate till the next step-up. I was wondering about pumping the spent wort off the top of the yeast cake, after I've chilled and the yeast has dropped out of solution. Don't know what would be the best type of pump, but I do have a small peristaltic pump. I'm guessing slowly lowering the suction tube as the spent wort level drops would create the least disturbance.... any thoughts about pumping? If I wanted to trial run the pumping method what would be a close substitute for yeast I could mix in water, that would drop out of solution when chilled? A yeast pack costs me around $8.00 and I can my starter wort in a pressure cooker so I don't want to waste that time and money if the pumping idea is a flop. >>Hope this group can help or direct me to the correct one. I grown yeast as >>part of my beer homebrewing process. I start with a 100ml yeast culture [quoted text clipped - 38 lines] >>loss. >>Please excuse my ignorance if I posted to the wrong group for advice. >Thanks Bob, one of the critical elements in brewing is keeping the yeast >from getting infected before it is pitched into the wort. The goal is having >the little critters at a high enough colony count to begin a rapid >fermentation when pitched into the wort. Infections during the yeast >stepping-up phase will create off-flavors in the finished beer. So every >transfer to another vessel runs the risk of infection. yes, yes. But I would think you could do this kind of step if you thought it important. If you already have a good, clean operation, this step is not difficult. Importantly, note that you do not need to transfer the entire yeast cake. You just transfer "all" the liquid, but at this point allowing some yeast to come over, too. In any case, if you see the logic of this step, fine. It is up to you to figure out a practical way to achieve the goal. >My current practice when stepping up the yeast growth is to flame the lips >of both flasks add fresh wort briskly, holding my breath during the transfer [quoted text clipped - 5 lines] >I'm guessing slowly lowering the suction tube as the spent wort level drops >would create the least disturbance.... any thoughts about pumping? Sounds good -- esp if you already have a pump. The logic you suggest for positioning the suction tube is good. You would probably further reduce disruption due to the suction tube if you could secure the suction tube on a rack, rather than simply holding it by hand. (In lab terms, a ring stand and clamp.) >If I >wanted to trial run the pumping method what would be a close substitute for >yeast I could mix in water, that would drop out of solution when chilled? Since the quality of the cake really depends on the material, there is no substitute for using the yeast. However, if you just want to play for a bit, try some mud. Occurs to me as I read your note... When you let the yeast settle, the flask is in its usual horizontal position? Try tilting it for the settling. Say 45 deg, to start, but eventually maybe more. This might help in two ways... Depending on the geometry, it might (or might not) lessen the surface area of the interface. In any case, it will mean less tilting during decanting, and thus you should disturb the cake less. Of course, you will have to arrange for something to support it. Hm, do you simply decant by hand? It might be better if you had a tiltable support, so you could tilt gradually and gently. Note that this could be of some use along with either decanting or pumping. bob |
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