Not enough O2 lead to off flavours??

[403Brewer]

I'm still somewhat new to the HB scene and am continually looking to improve my beers, my question is can not enough O2 during fermentation lead to poor flavours or what are the major drawbacks to a lack of O2 in the Wort, is it just incomplete fermentation? I do not use an Oxygenation system at the moment and I just want to justify purchasing one, the first year of home brewing is an expensive one (especially in Canada) so another $100 in gear is fine as long as I understand the benefits. Thanks!!

 

[shtoive87]

Oxygen will ensure the yeast propagates to the necessary cell count for the beer you brew. Personally, I shake the carboy for about 10 minutes to get oxygen in the wort. If you don't have enough cells, you could get incomplete fermentation or off-flavors from unintended esters. Hefeweizens often use a lower pitching rate because those ester profiles are appropriate for the beer. Basically, little oxygen is equivalent to pitching less. Also the yeast cell walls will suffer because they use the oxygen to strengthen their walls, which could affect the final product.

 

[erikpete18]

Yeah, a lack of O2 basically leads to less yeast growth, which results in stressed yeast and off-flavors. Depending on the yeast strain and style of beer you can sometimes get away with it, but its something to consider for improving your beers. How strong are your beers normally? For most normal gravity beers (~5-6% ABV), you can get by just fine with using regular air rather than oxygen. I just use an aquarium pump with a filter for the air hose, and its definitely a cheaper alternative to a full oxygen setup. (You can also shake/stir if you've got the arm strength and the confidence to take enough time to do it adequately.) I'll admit that I also use it for stronger beers and with a good-sized starter I haven't noticed too much in the way of off-flavors, but its something that I'm also planning on adding here at some point.

Edit: Another downside to less oxygen is that due to the lower level of yeast, you can get stuck/stalled fermentations and lower levels of attenuation, which can lead to beer that's overly sweet.

 

[EarlyAmateurZymurgist]

Can you describe the taste of the off-flavors?

 

[shtoive87]

It depends on the yeast. Lots of times it will be a strange fruity flavor. I accidentally did a massive under-pitching of WLP001 and got an over-powering fruity/cough syrup flavor. Kind of interesting, but certainly not what I wanted. Hefeweizens often give banana or clove type flavors. Belgians will give more tropical fruit type of impressions. Either way, esters will always be there, but if you under-pitch, they will be too strong for the style.

 

[grathan]

I think I find some the esters produced from lack of 02 desirable and plan to experiment more with not using any 02 at all. I do make a 2L starter though when using liquid yeast so I am pretty sure I am getting complete fermentations either way.

 

[BigFloyd]

You can always opt for dry yeast (depending on the style being brewed). Those cells are packaged with sterols that provide the needed O2 to carry them through the aerobic reproduction phase which precedes the anaerobic fermentation. It's best to rehydrate before pitching dry yeast.