Do you need to aerate typical gravity wort?

[LayMeister]

Another thread is talking about using olive oil to oxygenate. I noticed the following when reading through the Danstar site about Nottingham yeast:

" Nottingham British Ale yeast has been conditioned to survive rehydration. The yeast contains an adequate reservoir of carbohydrates and unsaturated fatty acids to achieve active growth. It is unnecessary to aerate wort."

and in a FAQ section on aeration:

"Yeast need a trace amount of oxygen in an anaerobic fermentation such as 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 a starter or into the mash, 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 beer this is no problem. It is when you produce higher alcohol beer 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.

If you prepare a starter culture you will need added O2. in the starter and perhaps in the main mash as a precaution. You will need to follow the precautions as mentioned above. If the mash is designed to produce 3-5% alcohol you may not need added O2. Brewing above that needs added O2."

 

[phissionkorps]

When I was a n00b, I didn't aerate, and fermentation would take days to start. Now I aerate the everliving hell out of every batch, and since then, I haven't had fermentation take more than about 5 hours to start, and I rarely if ever use starters.

 

[oguss0311]

Plus one to that- If you have a big starter and you aerate- you can see active fermentation Wicked fast. But I have read that if you do not do full boils- then the ice cold water that you add to make a full five gal will have enough O2 to get things going. I too have noticed the same thing that Phissionkorps reports- and you can have sluggish fermentation. If you follow the same procedure to aerate each time- it's one more variable that you can control and get consistency once you have the knack of it.
In regards to what you read- must say that it reminds me of gym class. It's way more fun outside. I'd aerate.

 

[Brew-boy]

If I cannot aerate a brew I wont brew that day. I always add O2 to every batch and make an appropriate size starter for cell count to gravity size. This is one of the best things that has helped me as a brewer make better beer.

 

[Joe Camel]

I believe that dry yeast needs neither aeration or a starter. Liquid yeast needs both.

 

[Yuri_Rage]

Technically, the answer is no, based on the yeast manufacturer's own verbiage.

However, most homebrewers will tell you that you REALLY need to aerate. Some will even suggest elaborate means of achieving oxygenated wort, up to and including filtered setups with oxygen bottles and porous stainless "stones."

Having used every method of aerating, from none to splashing to shaking to an elaborate oxygen rig, I notice little difference between ADEQUATELY PITCHED beer that is only aerated by a bit of splashing vs an one oxygenated with the bottle rig. I even know of one brew pub whose brewer does not worry much about aeration. It is PARAMOUNT that you treat your yeast kindly and pitch an appropriate amount of it. If you make a big liquid yeast starter or use a good dose of rehydrated dry yeast, aeration can be a lesser concern than if you were to simply sprinkle some dry yeast into the carboy or use a "pitchable" vial/pack of liquid yeast.

 

[Saccharomyces]

Wow, nothing left to say, Yuri hit it on the head.

Aeration is necessary for yeast growth. If you pitch enough yeast, aeration is not as important as if you are pitching a smack pack or tube without a starter. Dry yeast have the advantage of lots of cells (for a normal beer 1 pack is like pitching a decent sized starter of liquid yeast), and they have plenty of reserves already built up, whereas liquid yeast need to build their reserves up before they can get to work.

I still aerate with dry yeast to be on the safe side but I don't aerate much. Well, when I'm not totally anyway. Maybe 20 seconds of oxygen from an O2 bottle. With liquid yeast I will go for 1-2 minutes depending on the gravity.

 

[c1377]

If you pitch enough yeast, aeration is not as important...

Hear hear, O2 is needed for culture growth.

So why not just use 2 packets instead of one?

 

[Orfy]

Because at 2 packs it still need to grow and grow Healthily.

 

[Piotr]

Some beers reqiure some yeast growth in the fermenter, for flavour reasons.