Aeration on first fermenting

[growlrr]

What is the consensus on how often you aerate must during primary fermentation? I've seen everything from "pitch the yeast, give it a swirl and don't touch it for a month minimum" to "open it twice a day, drop in a power drill with a cato'nine tails and whip it until the battery dies or your arms fall off". Is there a difference for aerating needs between a basic mead and a melomel (a Perry in this case). Thanks!

 

[fossilcat]

The more oxygen you can introduce to the must early on regardless of your additives, fruits, spices, etc., the happier and healthier your yeast will be. The yeast is looking for sugar, it doesn't care if the honey carries it in or the fruit, it's gonna eat it and it enjoys oxygen while it's doing it.

 

[bernardsmith]

Great question. I suspect that most mead-makers aerate a couple of times a day but it is a little unclear to me whether such aeration in fact makes for a better fermentation (one with fewer off flavors) or a faster fermentation or whether it increases off flavors (due to oxidation). Honey, for whatever reason tends to be rather impervious to oxidation but fruits are not (slice an apple and it turns brown in a few moments - that is due to oxidation), although the volume of CO2 the yeast produce may serve to protect the fruit.

 

[Kody_Wulfe]

Yeah... I was wondering the same thing.. my first two batches were slow bubble scene.. next two I plan to aerate into submission.. HEHEHHE

 

[thm57]

Aerating in early days is very important in my opinion. I made a huckleberry mead 4 years ago when I was first starting to make mead. I used the same recipe in November but used SNA and aerated 1 or 2 times a day. The first one took about 8-10 months to be able to drink, the second was so good at 4 months that anything left after bottling this morning has already been drunk. Also there was an increase in ABV from 15% to 17%.

 

[bernardsmith]

Aerating in early days is very important in my opinion. I made a huckleberry mead 4 years ago when I was first starting to make mead. I used the same recipe in November but used SNA and aerated 1 or 2 times a day. The first one took about 8-10 months to be able to drink, the second was so good at 4 months that anything left after bottling this morning has already been drunk. Also there was an increase in ABV from 15% to 17%.

Right... but was the difference caused by your use of SNA (the nutrient protocol) or the aeration ... or both? Certainly, when you add fruit one problem is that the CO2 that the yeast produce force the fruit towards the surface. One way to ensure that the fruit then do not rot because of their contact with air and the relatively low moisture content of the surface is to frequently stir the fruit back down into the mead or wine. But if stirring to soak the fruit is all you are doing then how much O2 are you in fact adding? It is not entirely clear to me what the benefit is of true aeration is throughout the active period of fermentation. I stir but I don't really aerate and as a skeptical Scot and I want to know what the science is behind this activity - especially if I am making, say a low ABV mead with a large colony of viable yeast. Brewers don't aerate after pitching their yeast, do they?

 

[Baabaadoo]

Soo...What's the consensus?? There's still a lot of variation in the responses. New guy here just trying to figure things out. Just to set a biological context for thought here: I'm a biochemist so I know my biochem, but am a newb in home-brewing.

Yeast need oxygen for aerobic respiration, which I'm assuming is more preferred early on for yeast to replicate, but anaerobic (with oxygen present) does not produce ethanol.

So the question is: When is oxygen most beneficial for the yeast's health so we can then suffocate them into submission via aerobic respiration and get our desired fermentation outcome (desired ABV)?

Obviously, the goal is to get a clean fermentation (to the designated yeast strain's tolerance, not any earlier) and not introduce off flavors, right?

I don't know the answer, but it makes sense to me to introduce oxygen early for optimizing the reproductive phase of the yeast, but I fail to understand why to do it later on in the fermentation. As a newb, I think I'd rather not aerate at all and just see how my brews do.

 

[Maylar]

Your assessment is correct, in accordance with the most modern mead protocols. Aerate prior to pitching the yeast and once again after the lag phase. After that, regular stirring - both to degas (expel CO2) and to keep yeast in suspension - along with phased nutrient additions promotes the healthiest fermentation.

That's my understanding of the state of the art in mead.

 

[thm57]

So I think we are all in agreeance with the protocol Maylar layed out. The debate is over exactly what it is achieving. And that's a very good point about the sna Brenard, after some reflection the co2 would blanket the surface and reduce any oxygen input.

The science is also important to me, there's already enough myth around homebrewing and I try not to add to it if I can.

 

[bernardsmith]

My sense is that if you start with a large enough yeast colony (over-pitching is really harder than you might imagine)* then you may not need the yeast to reproduce so that after the initial uptake of O2 (that I believe the yeast need in the processes they use to strengthen their cell walls .. (?) ) I am not convinced that aeration has any real value. I guess the only way to really determine this is if enough mead and wine makers make enough wines and meads where they make identical batches of their wines/meads and where they aerate one batch with known volumes of O2 and don't add any O2 to the control batch and look for any differences - in off flavors, speed of fermentation, problems in fermenting etc. Stirring, by all accounts does not effectively aerate the must.
* Groennfell Meadery argues that if you are making five gallons of mead you want to pitch five packets of yeast...

 

[Maylar]

To add to the knowledge base, here's a quote from a dry yeast FAQ from Lallemand / Danstar -

(Link at http://www.danstaryeast.com/about/frequently-asked-questions)

I always aerate my wort when using liquid yeast. Do I need to aerate the wort before pitching dry yeast?

No, there is no need to aerate the wort but it does not harm the yeast either. During its aerobic production, dry yeast accumulates sufficient amounts of unsaturated fatty acids and sterols to produce enough biomass in the first stage of fermentation. The only reason to aerate the wort when using wet yeast is to provide the yeast with oxygen so that it can produce sterols and unsaturated fatty acids which are important parts of the cell membrane and therefore essential for biomass production.

If the slurry from dry yeast fermentation is re-pitched from one batch of beer to another, the wort has to be aerated as with any liquid yeast.

 

[bernardsmith]

But this is about aeration before pitching and not continually throughout active fermentation. The implication though is that O2 is critical for biomass production. The subtext is that if you are growing the colony then O2 may be important but if the biomass is already large enough when you pitch all you want to ensure is that the yeast cells remain viable not that they bud. In which case O2 (aeration) may be unnecessary - and if you are working with fruit may be potentially harmful if the oxygen oxidizes the fruit in ways that depress or spoil the flavor...

 

[fossilcat]

So do you fellas think more emphasis should be placed on building an appropriate biomass before pitch? Bray is pretty high on starters for liquid yeast, while you can just buy more dry yeast since it's cheap. I've been bumping into this subject on and off for the last year or so without really dedicating enough effort to understand - just sort of glossing over the subject. What bernardsmith says makes sense to me. So if O2 is only necessary to build the colony to a viable fermentation population then to build a better must it makes sense to do it as much as possible before the pitch, to avoid O2 exposure to sensitive additives like fruit. Besides, it's easier to introduce O2 to a 2 liter starter than a 5 gal must.

I'm adjusting my technique: My first feeding is after the lag phase, that will be my last effort to introduce O2. Thereafter, I'll stir to release CO2 and keep the yeast in suspension. We'll see how it goes.

 

[FunkyMunk]

I'm actually trying to figure out the same thing. I'm planning my first batch and listened to the podcast with Ricky from Groennfell Meadery after seeing this post . I gathered that he only aerates at the very beginning (which is what beer brewing typically entails). However, he's brewing "beer strength" (~8% ABV?) mead that is meant to be consumed fairly early, while the majority of the recipes I've seen (and the traditional mead I'm planning to make) generally have a much higher starting gravity and will finish with higher ABV (probably taking longer to get there). He also starts with a ton of yeast. I'm wondering if the decision to aerate only at the beginning, or throughout the primary fermentation, is dictated by how high of a SG you start with and how much yeast you pitch.

To me, it makes sense that oxygen is necessary during the lag phase, to allow the yeast to build the necessary biomass for the impending fermentation. However, what I don't know is whether oxygen is a requirement once fermentation is underway, or whether the yeast will continue to build more cells in a higher sugar/nutrient environment, thus requiring continued oxygen (I'm planning to use TOSNA 2.0 for SNA). Also, Ricky definitely railed against the oxygenation that is apparently rampant in mead. Most of what I've read on the interwebs suggests that oxygenation is not a problem... then again I've never drank their meads, and probably wouldn't recognize oxygenated mead even if I had.

The fact that they sell drill attachments for degassing wine also suggests that oxygenation (at least in primary) isn't a huge issue.

Sorry if this is my ignorance talking... I feel like all the reading I've done is just the tip of the iceberg, and I just want to not screw up my first batch.

EDIT: This post at gotmead.com addresses this issue, and seems to confirm my suspicion. Basically, the yeast continue to reproduce as long as there is enough oxygen to support it. In a lower alcohol beverage (i.e. beer) you only need so much oxygen to produce the yeast that can withstand that much fermentation. In contrast, wine (and stronger meads?) eventually reach a threshold, where more yeast cells are needed to handle the continued fermentation (i.e. the higher alcohol), and this is why more oxygen is needed in those ferments. However, there is still a point where additional oxygen is counterproductive -- no more yeast production is needed, and you're eventually going to cause off flavors due to oxygenation.

 

[Kody_Wulfe]

Finally.. a topic I can help with.. HEHEHE

After many a person told me that aeration is important.. I did that on my second and third batches.. and it helped my fermentation and gave the room a wonderful smell...

Kody