closed versus open fermentation

[VermontFreedom]

I have been reading completely contradictory indications about what system to use for primary fermentation: closed or open or airlocked, which I'll consider intermediary for the purposes of this thread.

More to the point, some directions I've read suggest that the wort or must requires oxygen and should be fermented in, for example, an open-top food-grade plastic bucket with at most a piece of cheesecloth over it just to keep a bug from falling in it. I have always done my primary fermentation within a bucket or carboy topped with an airlock. A recent set of instructions I read suggested sealing the primary fermenter with plastic and tying it down. What's up with that!!!


Anyway, looking for an explanation of (1) why these recommendations vary so widely (that is, an explanation of the theory behind why one would work better than another) and (2) what peoples experiences and recommendations are with these different techniques.

Thanks!

 

[Beer Snob]

Hmmm..... well I have never done an open fermentation. Some styles need it if you wanted to be right to the style... like Lambiacs for instance. Officially they are brewed with wild yeasts. I'm seriously looking into sour beers to give it a whirl, but I don't think I would ferment it with anything less then a closed system. I think there is too much of a probablity of the beer turning to vinegar. The main reason for closed systems I believe is to make sure that the specific yeast you add to the wort takes over. This is not to say that they would not take over in an open system, but there certainly is a greater chance of wild yeast doing the same.

Your point on worts requiring oxygen is dead on. But thats why you aeriate the wort when its cooled down. I'm trying to think of the books I have...... the ones I have certainly dont recommend anything less then a closed system. I think that if you used an open system that the consistency of the beer would change... you might have a greater percentage of batches that go bad for some reason.

 

[david_42]

People brew in closed systems to control the flavors the yeast contribute. Places where open ferments are normal are generally so saturated with the "style" strains, that they get consistant results without cultivating a specific yeast and bacteria strains. Any place where beer is brewed will have lactobacteria in the air, which will sour the ale.

As homebrewers, we want to control the yeast strain, hence closed fermentation after aireation.

 

[casebrew]

I don't think it's just saturation that protects from infection. Is it a Miller brewery near Magic Mountain that has external 'silo' fermenters? Look like a grain silo or three, with Krausen foaming out the top. A pillar of Krausen 30 feet round, and 20 feet tall blowing in the desert wind. My guess is that all that head is pushing unwanted invaders out of the fermenter. Then the beer is bottled and pasturised before it gets a chance to infect?

 

[sause]

I don't think it's just saturation that protects from infection. Is it a Miller brewery near Magic Mountain that has external 'silo' fermenters? Look like a grain silo or three, with Krausen foaming out the top. A pillar of Krausen 30 feet round, and 20 feet tall blowing in the desert wind. My guess is that all that head is pushing unwanted invaders out of the fermenter. Then the beer is bottled and pasturised before it gets a chance to infect?

Wierd I never see open fermentors at the miller plant in milwaukee. As a matter of fact if it's a lager than it needs to be in a controled temp enviroment. Leaving it out in the desert would definitly produce something wicked(yes, more wicked than it is).

 

[mysterio]

For primary, I use a bucket with the lid fitted on loosely. The beer is producing so much CO2 during the first few days that it 'blankets' the fermenting beer (as CO2 is denser than air). After a week to ten days or so I transfer it to a closed secondary fermenter. I've always brewed like this and the results are great so I have no reason to change.

Oh, with my lager I used a closed primary, because it took about 20 days or so to ferment out. However i'm sure I could've easily gotten away with an open fermentation - one of the main reasons I used a closed one was so I could move it about more easily.