Someone Explain Headspace to Me

Alright Folks, I have been reading a little here and there on the importance of head-space in primary and secondary fermentors.

Why does the amount of head-space matter in relation to the size of my batch?

What happens if there is too much head-space?

What happens if there is to little head-space, besides blow off?

OK so in a primary, you typically want more headspace, because that is when fermentation is active. If you have too little headspace, you will blow off krausen and potentially end up with an explosive beer device.

In secondary, the fermentation is mostly done and you're in more of a conditioning phase. In this case you want less headspace, because (at least initially after racking) more headspace means more oxygen, and you are trying to reduce the amount of oxygen that your beer is exposed to in order to prevent spoilage. Beer won't spoil right away in the secondary, but more exposure reduces the shelf life.

Too little in primary = possible blow-off

Too much in 2ndry = possible oxygenation (skunky) although I've never had a problem w/ that

In primary, you want sufficient headspace to allow the krausen (foam) to expand without coming out of your airlock. If it does, not a big deal you just rig up a blow off tube.

In secondary, you want as little headspace as possible so your beer is not exposed to air, this prevents unnecessary oxidation.

While you'd ideally want as little head space as possible in the secondary, I don't think it usually makes a difference. There's enough CO2 in the beer when you put it in there that it will push most, of not all, the O2 out of it. If there's any O2 in there, it'll be protected by a blanket of CO2.

Iniquity said:

Alright Folks, I have been reading a little here and there on the importance of head-space in primary and secondary fermentors.

Why does the amount of head-space matter in relation to the size of my batch?

What happens if there is too much head-space?

What happens if there is to little head-space, besides blow off?

Click to expand...

Headspace is the amount of air between the top of your beer and the airlock. This is important since after fermentation we want to keep the beer as free of oxygen as possible. If there is too much headspace then the risk of oxygen is greater, if there is too little headspace then you have a problem with blow-off and beer lost due to that.

Headspace in primary fermentation is not that important since fermentation releases a lot of CO2 which, since CO2 is heavier than air, will displace any air in the headspace. The issue arises during secondary and bottling. In secondary, where no actual fermentation occurs, headspace should be minimized to reduce air contact with the beer. Some CO2 will be given off, but not as much.

Hope that makes sense.

sp1365 said:

In secondary, where no actual fermentation occurs, headspace should be minimized to reduce air contact with the beer.
Hope that makes sense.

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First do not equate primary to aerobic and secondary to anaerobic. During aerobic fermentation the energy the yeast makes goes into budding and making more yeast cells. It used the O2 in the solution putting off CO2. Quite allot of CO2 gets dissolved into the solution. Under anaerobic conditions instead of putting energy into budding it goes into the production of alcohol. That is not to say it is one or the other but more that it does more growing in aerobic and more alcohol in anaerobic. As the solution around the cells becomes saturated with CO2 it forms bubbles that then float to the top.

The krausen is caused by primary fermentation, the bubbles are by secondary. It does not simply flip a switch and go from aerobic to anaerobic. It does this gradually as the O2 in the wort is used. CO2 is heavier then air so as long as you do not disturb the wort it will continue this progression gradually. This is the major argument for fermenting in the primary only.

So to claim there is no fermentation in the secondary is rather misleading. And depending on when you rack to secondary you could actually be fermenting more alcohol then you did in the primary.

what about bottling headspace? How much should be there? 1/4"? 1/2"?

motobrewer said:

what about bottling headspace? How much should be there? 1/4"? 1/2"?

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I use 3/4 to 1 inch just to be sure that the bottle doesnt pop its top.

Torg said:

First do not equate primary to aerobic and secondary to anaerobic. During aerobic fermentation the energy the yeast makes goes into budding and making more yeast cells. It used the O2 in the solution putting off CO2. Quite allot of CO2 gets dissolved into the solution. Under anaerobic conditions instead of putting energy into budding it goes into the production of alcohol. That is not to say it is one or the other but more that it does more growing in aerobic and more alcohol in anaerobic. As the solution around the cells becomes saturated with CO2 it forms bubbles that then float to the top.

The krausen is caused by primary fermentation, the bubbles are by secondary. It does not simply flip a switch and go from aerobic to anaerobic. It does this gradually as the O2 in the wort is used. CO2 is heavier then air so as long as you do not disturb the wort it will continue this progression gradually. This is the major argument for fermenting in the primary only.

So to claim there is no fermentation in the secondary is rather misleading. And depending on when you rack to secondary you could actually be fermenting more alcohol then you did in the primary.

Click to expand...

Not sure that I follow.

Yeast goes through a 5 stage life cycle; Lag, Growth, Stationary, Flocculation, and Dormancy.

Lag - Obviously the time between pitching and the growth phase.

Growth - This is the point where the yeast breaks down sugars and produces alcohol, CO2, flavors (esters, etc.), and heat. This is also the point where O2 and other nutrients in the wort are being consumed by the yeast. As the nutrients are used up the growth slows down till it hits the peak count.

Stationary - Peak cell count and yeast begins to store nutrients to survive.

Flocculation/Dormancy - Yeast falls out of suspension and is harvested/thrown out.

Secondary should not occur until after the flocculation of the yeast and thus the idea of a secondary "fermentation" is untrue. Beer should not be transfered until the beer has fully fermented out and the final attenuation has been achieved. This is why the suggestion is made that beer not be transfered until SG has been measured 3 consecutive days without change.

sp1365 said:

Not sure that I follow.

Yeast goes through a 5 stage life cycle; Lag, Growth, Stationary, Flocculation, and Dormancy.

Lag - Obviously the time between pitching and the growth phase.

Growth - This is the point where the yeast breaks down sugars and produces alcohol, CO2, flavors (esters, etc.), and heat. This is also the point where O2 and other nutrients in the wort are being consumed by the yeast. As the nutrients are used up the growth slows down till it hits the peak count.

Stationary - Peak cell count and yeast begins to store nutrients to survive.

Flocculation/Dormancy - Yeast falls out of suspension and is harvested/thrown out.

Secondary should not occur until after the flocculation of the yeast and thus the idea of a secondary "fermentation" is untrue. Beer should not be transfered until the beer has fully fermented out and the final attenuation has been achieved. This is why the suggestion is made that beer not be transfered until SG has been measured 3 consecutive days without change.

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Well the stages you point out are not start and stop times. The process I posted was about how fermentation works and how alcohol is made. It is a metabolic process but I did not want to actually post what enzymes do what process. It would be easier to say what I posted is what you posted as the Growth stage.

However it does not simply flip a switch and go to growth. Depending on a few factors (mainly fermentation temperature) the amount of time it takes to start producing trub is somewhere in the middle of your growth stage.

I was not implying when a person should rack to secondary or even if they should or should not rack. What I was saying is you can not exactly equate each phase as a definitive line. The yeast does not automatically switch. And you will have yeast cells going dormant while you have other cells budding.

You can kick fermentation back into gear simply by adding more sugar. This is exactly what priming sugar does. There are brewing techniques that repitch yeast and malt in the middle of brewing. I have seen it done especially in higher gravity beers (more like extreme gravity beers).

But all of this is way off the topic of how much head space should you use.

Torg said:

First do not equate primary to aerobic and secondary to anaerobic. During aerobic fermentation the energy the yeast makes goes into budding and making more yeast cells. It used the O2 in the solution putting off CO2. Quite allot of CO2 gets dissolved into the solution. Under anaerobic conditions instead of putting energy into budding it goes into the production of alcohol. That is not to say it is one or the other but more that it does more growing in aerobic and more alcohol in anaerobic.

Click to expand...

Aerobic fermentation is an oxymoron. Yeast is a eukaryote like us, fermentation only takes place in anaerobic conditions, in aerobic conditions its called respiration with the products being CO2 and H2O.