Newbee questions about heating and aeration

Welcome WorkSpace!

Good questions, and as you read more of the zillions of posts you're bound to find lots of opinions.

In a nut-shell, GotMead folks recommend NOT heating the must. As you said, honey is pretty darn clean. Moreover, heating will only destroy the delicate aromas of honey. Advice to heat is usually due to either historical recipes or recipes stemming from beer-brewing practices, both of which use heat during must/wort preparation.

Aeration is more important in mead than in other fermentations since honey is almost devoid of natural nutrients (which helps with the biologically clean part). Oxygen is needed to build up strong cell walls. As you said, a big healthy yeast pitch would reduce the oxygenation requirements. Not knowing exactly how you like to prepare your yeast, I can't comment on whether you'd need to do much additional aeration. The best thing you can do is a pair of batches, one with extra aeration and one without. No substitute for personal experience! (and be sure to post your results)

Again welcome and let us know what your first batch will be!

Welcome to the forums WorkSpace!

Your are quite correct that honey is clean stuff - very little can survive in it, and those things that can are destroyed by the osmotic shift when you dilute the honey with water, so there is no need to heat honey musts. In fact, it may be detrimental as you boil off aromatic elements that you want to keep. You'll find most folks here don't heat other than a little warming to make the honey easier to pour.

As for the aeration, there have been good studies in wine that explain the need for aeration/oxygen. The oxygen stimulates the yeast to form more sterols that strengthen the cell membrane, allow for more efficient division, promote increased tolerance to alcohol, and allow nutrients to be taken in and utilized late in the fermentation. Completely anaerobic fermentation results in lower amounts of sugar utilization unless the must is supplemented with sterols and long chain fatty acids. Allowing air will actually speed the fermentation. For meads it seems to work the same. Pitching more yeast will not make them stronger or more alcohol tolerant. In wine, oxygenation on day 2 of fermentation seems to be the critical window, but typically folks here will aerate during the first 2 or 3 days - or up to the point that the gravity has dropped by 1/3 (the 1/3 sugar break).

I hope that helps, and if you continue using the search tool you will find much more discussion on these topics.

Good meading!
Medsen

WorkSpace said:

Hello from down-under :wave: . This is my first post here, and I haven't made mead before. So I have been reading the newbee guide and some relevant threads. As an extract beer, wine and spirit wash brewer, I have been trying to make sense of the process. Two aspects of it seem odd to me, and maybe you could explain what I am missing.

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WELCOME TO GOT MEAD?!

WorkSpace said:

I am trying to understand why it should be necessary to heat the must. I understand that this is done to get rid of natural yeasts and micro-organisms. But I would have thought that honey is pretty clean stuff. We have jars of it that has been sitting on the shelves for years, and it is still fine. What happens if the must isn't heated. Has anyone done both and compared results?

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Heresy! Not heating the must???? Are you mad man???? LOL

J/K LOL - In fact you'll find most of us here don't heat their must in part because honey is indeed very clean (inherently very bacteriostatic due to the low amount of water) but more because when you heat honey you cook off the enzymes, proteins and delicate floral characters and other volatile aromas that translate more complexity and flavor into your mead.

WorkSpace said:

The other thing I couldn't understand was aeration during the fermentation process. Is this really necessary? With all the beer, wine and spirit washes I have made, I have never done this. After pitching the rehydrated yeast, the fermenter is closed up, the airlock is fitted and it is left alone for about a month (depending on temperature). I know aeration is done to promote yeast growth. But wouldn't it be better to ensure that adequate yeast is available before fermentation starts? I would have thought that interfering with the fermentation process would be counter-productive.

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Actually the reason that we aerate is to not only promote yeast growth, but because as generations of new yeast are produced during fermentation, those new generations need a constant supply of oxygen in order to form strong cell walls with other components (sterols, etc.) and keep the cell wall supple and flexible. If the cells do not get adequate supplies of oxygen and nutrient the cell walls will become brittle and they will not form enough strength to regulate osmotic pressure and will undergo premature autolysis. During that time before they do die off they will be stressed from lack of oxygen and nutrient and produce off flavors. When you see a mead fermentation that lasts more than a couple of weeks what you're seeing in many cases is an under aerated and nutrient deprived fermentation.

From a recent SO2 in Wine lab report I did:
...snip...Molecular oxygen serves as a micronutrient for many organisms, required for the biosynthesis or degradation of many compounds. PPO successfully competes with the microbes present in wine for O2. Oxygen is required by the yeast for optimal ethanol tolerance (this is why we aerate in order to get O2 into the must for the yeast so they can synthesize sterols to strengthen the cell walls and have a higher ETOH tolerance), if PPO activity is unchecked, the yeast may be in a nutrient deficient situation (in this case O2 as a nutrient). This is an additional reason to add SO2 in grape musts. It is not clear at the molecular level exactly how SO2 is able to inhibit PPO activity....snip...

OK, we're dealing with honey vs grape must here and the rate of aeration and stages of aeration are going to be different. With grapes you're dealing specifically with a couple of anti-oxidants that will compete with with yeast for oxygen as the skins are in contact with the juice (most specifically PPO - Polyphenoloxidase) While you don't have that in honey must, you do have higher osmotic pressure so a couple of aerations daily during the first 1/3 of the ferment is beneficial (in order to build strong cell walls) and will not present risk of oxidation because the oxygen is being stripped from the yeast cells by the rapid production of CO2.

From Dr. Clayton Cone of Lallemand:
Yeast need a trace amount of oxygen in an anaerobic fermentation such as meadmaking, winemaking and brewing to produce lipids in the cell wall. With out O2 the cell cannot metabolize the squalene to the next step which is a lipid. The lipids make the cell wall elastic and fluid. This allows the mother cell to produce babies, buds, in the early part of the fermentation and keeps the cell wall fluid as the alcohol level increases. With out lipids the cell wall becomes leathery and prevents bud from being formed at the beginning of the fermentation and slows down the sugar from transporting into the cell and prevents the alcohol from transporting out of the cell near the end of the fermentation. The alcohol level builds up inside the cell and becomes toxic then deadly. Lallemand packs the maximum amount of lipids into the cell wall that is possible during the aerobic production of the yeast at the factory. When you inoculate this yeast into your must, the yeast can double about three time before it runs out of lipids and the growth will stop. There is about 5% lipids in the dry yeast.

In a very general view:
At each doubling it will split the lipids with out making more lipids (no O2). The first split leaves 2.5% for each daughter cell. The second split leaves 1.25% for each daughter cell. The next split leaves 0.63%. This is the low level that stops yeast multiplication. Unless you add O2 the reproduction will stop. When you produce 3-5% alcohol beverage this is no problem. It is when you produce higher alcohol beverage or inoculate at a lower rate, that you need to add O2 to produce more yeast and for alcohol tolerance near the end of fermentation. You definitely need added O2 when you reuse the yeast for the next inoculum.

Dr. Clayton Cone


References:
Texts:
Bisson, L., 2005. VEN 124 Wine Production for Distance Learners, Lesson 5: Juice and Must Treatments and Additions Topic 5.2: Juice Additions
Boulton, R., V. Singleton, L. Bisson, and R. Kunkee. 1996. Principles and Practice of Winemaking. Chapman and Hall. New York
Peynaud, Emile, 1984. Knowing and Making Wine, (English Translation) John Wiley and Sons, Inc. USA

Journal Articles:
Baldwin, G., Basic Effects of Sulfur Dioxide on Yeast Growth. American Journal of Enology & Viticulture Volume 2: 45–53. 1951
Cocolin, L., and D.A. Mills Wine Yeast Inhibition by Sulfur Dioxide: A Comparison of Culture-Dependent and Independent Methods. Am. J. Enol. Vit. 54: 125 – 130. 2003

Other Articles:
Delteil, D., Enological yeast effect on the sulfur dioxide content and management in wines. Institut Cooperatif du Vin, 1 – 4 1992

WorkSpace said:

Introducing air slows fermentation, and opening the fermenter increases the risk of contamination. What happens if you don't aerate?

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Introduction of air does not slow fermentation. Opening the fermenter does indeed increase the risk of contamination, but with proper aseptic technique that possibility is heavily mitigated. If you don't aerate you'll run into issues as outlined above.

WorkSpace said:

I hope this doesn't sound too argumentative. I just need to understand why things have to be done. ???

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Not at all, they're good questions. I hope my answers will help you decide to try something different and compare your results in a blind tasting with friends and other mead makers.

Cheers,

Oskaar

Well, I'm coming late to this party, but let me add my welcome to the chorus! You've stumbled on the most comprehensive compendium of mead information in the world here at GotMead, so it is understandable that if you have perused the forum postings as well as read the newbee's guide, you have seen some of the evolution of thought and the results of research performed specifically on fermentation kinetics in mead musts over the past several years. We've all revised our processes based upon the information that we've gleaned, and our own experiences that we've shared, in recent years. As you've probably seen, Oskaar is the best single source of detailed data to support all the techniques espoused here -- without him, we'd still be in the meadmaking Dark Ages. But the evolution of process that occurs amongst the participants of this forum is truly a group effort, so we tend to have access to the best current thoughts of the meadmaking community as a whole.

Your question about heating has obviously been put to rest -- heating was an old technique that has fallen out of favor in recent years as we have learned that it is not necessary, and may be detrimental, to the results.

The issue of oxygenation of mead must is a newer concept, borne of both recent research into optimization of wine fermentation as well as our personal experiences, having done batches of mead both with and without various aeration techniques applied. The bottom line is that mead musts, for all the reasons cited by Oskaar and Medsen, benefit greatly from the addition of oxygen into the must between yeast pitch and approximately the 1/3 sugar break (the point at which 1/3 of the fermentable sugar has been consumed by the yeast). That might be counter-intuitive to anyone in the hobby for a number of years -- it certainly took me a while to come around to adopting the process -- but the results that I've achieved using early aeration of mead musts have been nothing short of phenomenal! First, primary fermentation times have been cut from weeks (or months) to just days for musts of all starting gravities. Second, and more importantly, my resulting meads taste better! Under those circumstances, I will never "pitch and forget" a mead must into a closed carboy again.

Well, before you buy anything why don't you post up your idea for a recipe and we'll help you fine tune it to something that will be a great first batch.

Cheers,

Oskaar

Welcome to the forums and congrats on what will hopefully be a new obsession. I'm pretty new to mead making myself and I'd like to direct you toward a book by Ken Schramm.

http://www.amazon.com/Compleat-Mead...bs_sr_1?ie=UTF8&s=books&qid=1212124727&sr=8-1

Long link heh. I've seen a few posts by Mr. Schramm here on the forums and this isn't a shameless plug for his book or anything hehe. I highly recommend his book and some constant usage of the search tool here on gotmead.com. So far everything I know about mead making has come from one or both sources. Good luck and happy mead making sir

STOP STOP STOP!

Whatever you do don't add any acid up front.

Acid will drive the pH of the must down and more than likely stress your yeast and in turn cause your fermentation to limp along slowly or stall altogether. This is an old, brewer's approach to meadmaking and is not recommended.

The internal pH of a yeast cell is near neutrality (pH 6.5- 7.0), while the pH of the medium is 3.0 to 4.0. This creates a large gradient of protons, and entry of hydrogen ions into the cell is energetically favorable. Therefore, movement of amino acids is coupled with that of protons. Amino acid transporters transfer both an amino acid molecule and a proton into the cell. The proton is then exported out of the cell via a proton pump. The pump extrudes protons in an energy dependent manner since excretion occurs against the proton gradient.(Bisson 2005)

Hydrolysis of ATP provides the energy for operation of the pump. Continued amino acid uptake requires efficient excretion of the protons that are being co-transported with the amino acid; so amino acid uptake is a very energy intensive process.

Since amino acid uptake is coupled to protons it's no mystery that the pH of the medium (must in this case) affects amino acid uptake. If the pH is too low, below 2.7, protons tend to enter the cell due to passive proton flux. The proton pump must then be directed towards removal of these protons. The cell has a limited capacity for the removal of protons, thus at very low pH the cell is not able to sustain amino acid uptake due to the lack of capacity of the proton pump.

There are several other factors that impact fermentation and H2S production that are associated with pH as well, most of them are NOT good for your mead.

Hope this helps and that you read this BEFORE making that acid addition. I'd also hold off on the tannin until the end.

Cheers,

Oskaar

And if THAT doesn't help...Stable versions of Newton & Apos's iteration for computing the principal matrix pth root A1/p of an n x n matrix A are provided. In the case in which X0 is the identity. A parallel fast direct solution method for linear systems with separable block tridiagonal matrices is considered. Such systems appear, for example, when discretizing the Poisson equation in a rectangular domain using the five-point finite difference ...

:cheers:

:notworthy:

Since Oskaar's offline at the moment, I can answer your question about aeration. The yeast need oxygen from the must during their exponential growth phase, and partly into the stationary phase, in order to produce the sterols that keep yeast cell walls flexible and permeable. Without a source of O2, as yeast bud and divide to reproduce, the available lipids (sterols) in each cell goes down, as the total quantity is shared by the parent and all daughters. This leads to the cell walls becoming less flexible, and harder to exchange fuel for waste products. As a result, the yeast will work harder, and exhaust themselves sooner, than if the proper amount of sterols are available for each cell.

So, oxygen in the first 1/3 of fermentation (the period when the first 1/3 of fermentable sugars are consumed), which corresponds to that exponential growth phase, is a very good thing. You can oxygenate by injecting pure gaseous O2 into the must, or you alternatively may aerate with forced air through an airstone, or simply vigorously stir the must, splashing as much as practical, to mix as much room air with the must as possible. Do this immediately prior to yeast pitch, and then at least once daily thereafter until the 1/3 sugar break has been reached. I actually aerate via an aquarium pump and sanitized airstone for 30 minutes prior to pitching, and I do the vigorous stirring approach post-pitch with most of my meads, performing it twice daily, for about 5 minutes per shot.

After the 1/3 sugar break your yeast are pretty well along in the anaerobic stationary phase, and adding more O2 does little to help them, and can actually end up oxidizing the mead. So, O2 (or air) is good early on, but undesirable thereafter.

Hello Workspace,

I'm glad to hear your batch it off and running!

If I understand it correctly, fermentation is an anaerobic process.

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While fermentation is anaerobic, the presence of oxygen does not stop fermentation. In wine or mead musts, the high sugar content inhibits the yeasts' ability to utilize oxygen for energy generation, so it keeps fermenting the sugar as its source of energy. Even though the fermentation won't be stopped by air exposure, as Wayneb pointed out, after the 1/3 sugar break (the point where the yeast have consumed 1/3 of the sugar in the must), exposure to air and oxygen won't be helpful and may cause oxidized aromas (acetaldehyde) and flavors in your mead.

When you vigorously stir (or Whack The Crap out of it) you will de-gas the must and it may take a few hours for the CO2 to build back up and start bubbling again.

I hope yours turns out well.
Medsen

Medsen Fey said:

Hello Workspace,

I'm glad to hear your batch it off and running!

If I understand it correctly, fermentation is an anaerobic process.

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While fermentation is anaerobic, the presence of oxygen does not stop fermentation. In wine or mead musts, the high sugar content inhibits the yeasts' ability to utilize oxygen for energy generation, so it keeps fermenting the sugar as its source of energy. Even though the fermentation won't be stopped by air exposure, as Wayneb pointed out, after the 1/3 sugar break (the point where the yeast have consumed 1/3 of the sugar in the must), exposure to air and oxygen won't be helpful and may cause oxidized aromas (acetaldehyde) and flavors in your mead.

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I think you're referring to the Crabtree effect? Here's a quick Wikipedia description:

http://en.wikipedia.org/wiki/Crabtree_effect

Named after the English biochemist Herbert Grace Crabtree, the Crabtree effect describes
the phenomenon whereby the yeast, Saccharomyces cerevisiae, produces ethanol (alcohol)
aerobically in the presence of high external glucose concentrations rather than producing biomass
via the tricarboxylic acid cycle, the usual process occurring aerobically in most yeasts eg.
Kluyveromyces spp [1]. Increasing concentrations of glucose accelerates glycolysis (the breakdown
of glucose) which results in the production of appreciable amounts of ATP through substrate level
phosphorylation. This reduces the need of Oxidative phosphorylation done by the TCA cycle via the
Electron Transport System and therefore decreases oxygen consumption. The phenomenon is
believed to have evolved as a competition mechanism (due to the antiseptic nature of ethanol)
around the time when the first fruits on Earth fell from the trees [2].

Welcome to the forums WorkSpace!

Thanks for chiming in Dan!

Hey Workspace, here's from one of my earlier posts about fermentation during the anaerobic phase. This is from Dr Clayton Cone of Lallemand who is the reigning yeast guru in the wine industry.

Oskaar said:

From Dr. Clayton Cone of Lallemand:
Yeast need a trace amount of oxygen in an anaerobic fermentation such as meadmaking, winemaking and brewing to produce lipids in the cell wall. With out O2 the cell cannot metabolize the squalene to the next step which is a lipid. The lipids make the cell wall elastic and fluid. This allows the mother cell to produce babies, buds, in the early part of the fermentation and keeps the cell wall fluid as the alcohol level increases. With out lipids the cell wall becomes leathery and prevents bud from being formed at the beginning of the fermentation and slows down the sugar from transporting into the cell and prevents the alcohol from transporting out of the cell near the end of the fermentation. The alcohol level builds up inside the cell and becomes toxic then deadly. Lallemand packs the maximum amount of lipids into the cell wall that is possible during the aerobic production of the yeast at the factory. When you inoculate this yeast into your must, the yeast can double about three time before it runs out of lipids and the growth will stop. There is about 5% lipids in the dry yeast.

In a very general view:
At each doubling it will split the lipids with out making more lipids (no O2). The first split leaves 2.5% for each daughter cell. The second split leaves 1.25% for each daughter cell. The next split leaves 0.63%. This is the low level that stops yeast multiplication. Unless you add O2 the reproduction will stop. When you produce 3-5% alcohol beverage this is no problem. It is when you produce higher alcohol beverage or inoculate at a lower rate, that you need to add O2 to produce more yeast and for alcohol tolerance near the end of fermentation. You definitely need added O2 when you reuse the yeast for the next inoculum.

Dr. Clayton Cone

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Basically as budding occurs, the new generation of yeast needs oxygen. Oxygen in trace amounts will not slow or stop the anaerobic cycle, but will in fact help the yeast to ferment more rapidly and aggressively. Also of note is that during the aerobic and the early anaerobic phase of fermentation the yeast will produce up to and above 30 times the amount of ethanol that will be produced in the rest of the fermentation. This in the presence of oxygen, especially during the first 72 hours of fermentation. Hence, oxygen will not slow, stall, impede or otherwise muck up the works for a good strong anaerobic ferment after most of the alcohol has been produced in the early stages.

Hope that helps,

Oskaar

As for the aeration, there have been good studies in wine that explain the need for aeration/oxygen. The oxygen stimulates the yeast to form more sterols that strengthen the cell membrane, allow for more efficient division, promote increased tolerance to alcohol, and allow nutrients to be taken in and utilized late in the fermentation. Completely anaerobic fermentation results in lower amounts of sugar utilization unless the must is supplemented with sterols and long chain fatty acids. Allowing air will actually speed the fermentation. For meads it seems to work the same. Pitching more yeast will not make them stronger or more alcohol tolerant. In wine, oxygenation on day 2 of fermentation seems to be the critical window, but typically folks here will aerate during the first 2 or 3 days - or up to the point that the gravity has dropped by 1/3 (the 1/3 sugar break).

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I am so thankful to have found this site, already! I have made all of mine with one heavy oxygenation at the time to pitching yeast. I learned from Ken Schramm's book and he instructs the reader to vigorously shake and then lock. I can't find any advice in the book regarding subsequent aeration (I may have missed it, but have re-read it a couple of times). I'm so glad to find this out! I'm starting two batches today and will repeatedly aerate.

I have a question regarding this: when you say "folks here will aerate during the first 2 or 3 days - or up to the point that the gravity has dropped by 1/3 (the 1/3 sugar break)", does that mean that the Specific Gravity drops by 33 of the 100 points that it 'ideally' should drop during fermentation? Or is it 1/3 of something else?

I expect that the 33/100 is right (it's certainly logical), but having missed out on what now seems so glaringly obvious and sensible a technique makes one a bit cautious. I'd rather ask a 'silly' question than miss the information ...

Thanks Again, both to Workspace for asking the question and for so many others for answering it!


Earendil

Earendil,

For simplicity sake if your mead starts out with a brix of 30 take that number and divide it by three, which equals 10 (aka 1/3 or 33%) Then subtract that from the total to get the 1/3 sugar break.

e.g. 30 brix starting divided by 3 = 10 (30/3=10) then to determine the 1/3 sugar break, Original brix - one-third brix (30-10=20) so 20 brix is your 1/3 sugar break, and then 10 brix would be your 2/3 sugar break.

That's why I work mostly in brix, I hate decimals!

Cheers,

Oskaar