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Thread: Aeration

  1. #1
    Join Date
    Aug 2005
    Location
    Milwaukee, WI
    Posts
    908

    Default Aeration

    Aeration is important for providing the reproducing yeasts with the oxygen they need. It is therefore important to aerate well when mixing the must. Per GM expert oppinion, additional aeration over the next couple of days helps as well.

    My question is, for how long do I shake the gallon jug to aerate it during the 2-3 days after mixing? From what I am observing, most of what happens is that I am removing the CO2 that is dissolved in the liquid (geyser eruption ensues with loss of liquid ) During preparation of the must, I shook for a good 5 minutes. Do I have to do the same during additional aerations?

    Also, found a post out there that discussed the addtion of yeast husks as a substitute to aeration as these provided the reproducing yeasts with the lipids they need for strong cell wall growth. Is this on track and which method produces the better mead (personal oppinion and taste are obviously a factor here, but still interested to see what you all think).

    Thanks,

    Angus
    Chan fhíach cuírm gun a còmhradh

    A feast is no use without good talk.

  2. #2

    Default Re: Aeration

    What I've read, says to stir or shake a couple times a day, I can't recall anything as to how long.

    With an open fermentation, gas exchange is exactly what we're after when we aerate. As the surface of the must is agitated Co2 escapes and O2 enters.

    If must comes out of the container with the gas a larger primary fermentor might help. For 1 gallon runs, I use a 2 gallon food grade bucket covered with sanitized flour sack cloth. Once or twice a day, I'll remove the cloth from the bucket and stir the must with a whisk (sanitized).

    What I recall of yeast hull/ghost is of their use as a nutrient.

    Anthony


  3. #3

    Default Re: Aeration



    Quote Originally Posted by Angus
    Aeration is important for providing the reproducing yeasts with the oxygen they need. It is therefore important to aerate well when mixing the must. Per GM expert oppinion, additional aeration over the next couple of days helps as well.

    My question is, for how long do I shake the gallon jug to aerate it during the 2-3 days after mixing? From what I am observing, most of what happens is that I am removing the CO2 that is dissolved in the liquid (geyser eruption ensues with loss of liquid ) During preparation of the must, I shook for a good 5 minutes. Do I have to do the same during additional aerations?

    Also, found a post out there that discussed the addtion of yeast husks as a substitute to aeration as these provided the reproducing yeasts with the lipids they need for strong cell wall growth. Is this on track and which method produces the better mead (personal oppinion and taste are obviously a factor here, but still interested to see what you all think).
    Hello Angus -- no, yeast hulls aren't a substitute for oxygen. They help give a nutrient boost during that that key phase when they're stirring about and getting themselves ready for the big fermentation, but it's really oxygen they need to help build the yeast walls up properly.

    Shaking the jug -- it'll take a *lot* of shaking to equal the amount of O2 dissolved into the must by 20 minutes with an airstone. Shake it up good, shake it up some more.

    There was a lot of discussion on this subject on the HomeBrew Digest some time ago.

    <><><><><><><><><><>
    <><><><><><><><>
    Dan McFeeley

    "Meon an phobail a thogail trid an chultur"
    (The people's spirit is raised through culture)

  4. #4

    Default Re: Aeration

    As Dan noted, shaking a gallon jug in the hope of introduction oxygen into the must will do little more than exercise a few muscles. To effectively infuse oxygen requires a pump and an air stone, or a tank of pure oxygen and a diffusing stone (usually made from stainless steel).

    The latter setup is what I use ~24 hrs after the start of active fermentation - a 90 sec blast. My last 2 meads reaction to this infusion was quite effective. However, I also rehydrate my dry yeast and follow a staggered nutrient addition schedule.

  5. #5
    Join Date
    Dec 2004
    Location
    The OC
    Posts
    7,874

    Default Re: Aeration

    Angus,

    For shame for shame,

    You haven't been doing your homework and link reading! LOL

    Follow this link to a previous discussion:

    http://www.gotmead.com/index.php?opt...12561#msg12561

    Hope that helps.

    Yeast hulls provide lipids, and help to increase the surface area so your yeasties can stay in suspension longer, and have more to chew on.

    Cheers,

    Oskaar
    Is it tasty . . . precious?

  6. #6

    Default Re: Aeration



    Some good info is here:

    http://winemaking.jackkeller.net/feeding.asp
    Yeast Ghosts (Yeast Hulls)
    Consists of the insoluble fraction of whole yeast cells, namely the cell wall and membrane. These materials supply lipids and sterols to the fermenting yeast and adsorb fatty acids which may cause sluggish fermentations. They will improve vinegar and malo-lactic fermentations as well. The use of yeast ghosts seems to reduce the incidence of hydrogen sulfide. Normal use is 1 to 2 lbs per 1000 gallons or 0.45 to 0.9 gram per gallon. At rates above 3 grams per gallon off flavors and aromas have been noted on occasion.

    and here:

    http://www.lallemand.com/Oenology/Im...1Stuckferm.pdf

    <><><><><><><><><><>
    <><><><><><><><>
    Dan McFeeley

    "Meon an phobail a thogail trid an chultur"
    (The people's spirit is raised through culture)

  7. #7
    Join Date
    Aug 2005
    Location
    Milwaukee, WI
    Posts
    908

    Default Re: Aeration

    Thank's everyone. In summary then:

    1. Aeration can be acheived through shaking, stirring, pouring through a funnel into another vessel, or by using a stainless steel air-stone and either a pump with a sterile filter or pure O2.
    2. Aerate well during must preparation by shaking hard for 5 minutes or so or by pouring back and forth between two vessels through a funnel (gallon jug method); using a power stirrer attchament or whisk (5 gallon method); using an air-stone and O2 source (any size).
    3. Oxygen is needed during the Exponential Growth phase, between 24 and 72 hours into fermentation, to ensure healthy growth and strong cell walls. Aerate again during this period.
    4. There is no substitution for aeration! Growing yeasts need O2.

    Another toy to buy then. (Saw the owners of my LHBS drive by in a Ferrari the other day. They waved and thanked me )

    Don't know how I missed all of the links either (guilty as charged Oskaar). Of course, I was searching the night of the Ancient Orange party, so that may have been a factor :P :P

    Angus
    Chan fhíach cuírm gun a còmhradh

    A feast is no use without good talk.

  8. Default Re: Aeration

    Here are links to a couple of detailed articles concerning yeast cell wall construction: http://jb.asm.org/cgi/content/full/180/15/3735
    http://www.pubmedcentral.nih.gov/pic...9&blobtype=pdf

    Both oxygen and growth components such as lipids are required during the aerobic-phase of yeast growth. The cells need to divide in order to increase their numbers and dominate the culture. In addition, formation of a good cell wall is important to insure that the yeast will remain healthy during anaerobic fermentation and can withstand the resulting high alcohol conditions. Lipids, etc. serve to provide the building blocks for a good cell walls. Oxygen is also a component but its main function is to act as the final electron receptor in the process that provides the energy that is necessary for cell growth/ division/ cell wall formation.

    How much oxygen is necessary is debatable. As usual, the short answer is that it depends upon your specific must/ yeast/ growth conditions. If oxygen does become limiting, the result will be low cell numbers. However, if other key nutrients were available these low cell numbers can still be hardy enough to carry out anaerobic fermentation/ alcohol formation.

    If oxygen is not limiting, you will have good cell numbers. However, this will mean little if other nutrients were limiting and good cell walls were not formed. The result will be a high cell population that quickly poops out once anaerobic fermentation/ alcohol formation begins.

    Excessive aeration will shorten your meadmaking process, but it can also be detrimental. Culture characteristics are different during aerobic growth and a build up of end products produced can affect final flavor. Also, sugars are broken down completely during aerobic growth and are not converted to alcohol. So any calculations you have done with a specific starting S.G. to determine final A.B.V. will be thrown off by an extended aerobic growth phase.

    Sparging with pure oxygen can be damaging as well. In its natural environment, a yeast should not see oxygen levels above 20%. When the oxygen level increases significantly above 20%, it can become lethal to yeasts. Without a calibrated dissolved oxygen probe, it is difficult to determine the amount being introduced through pure-O2 sparging...There are a lot of variables that affect O2 transfer such as bubble size, sparge rate, liquid height, temperature, overpressure level, rate of consumption by the culture, et cetera. Keeping this in mind it is always better to err on the low side when adding pure oxygen.

    Fortunately, the range of "acceptable" levels of aeration and nutrient is broad enough the average homebrewer using standard techniques will not have much of a problem. FWIW, I personally aerate my must to saturation just before pitching and do not muck with it again. Whether I go into anaerobic fermentation with 8 logs of cells vs. 9 logs (if I aerated further) doesn't really matter to me as long as the population is healthy and happy.


    Peace.

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