Primary Fermentation and Stirring

[dcteague]

So I just read a blog from someone on here about yeasts and their cycle during fermentation. It generated some questions I have regarding the use of airlocks during primary.

I've always just assumed that having the primary under airlock and stirring was okay - haven't had any issues with fermentation on the batches I've done (on my 3rd), but the blog I read indicates that as the initial phase of yeast ends (yeast reproduction), the lack of oxygen is good because they eat the sugar thereby producing alcohol and without oxygen, they stop replication. If oxygen is present however and replication hasn't ended, they will use the sugar to replicate, and use the oxygen as a food source? I'm assuming that when only sugar is present, there's nothing to allow for replication, and they just eat and die.

So, if I have my primary under airlock, and fermentation is proceeding well, it seems to make sense that at some time during the first week, I should stop stirring, and just allow the fermentation to proceed un-interupted. Otherwise, the stirring will introduce oxygen, and impede alcohol production.

So the big question is:

How do you know when to stop stirring and introducing oxygen. What visible or other perceivable observation can be made that would tune you into this point in time? I've simply been fermenting to the point where my bubbler slows to an acceptable rate, then I rack and stop stirring. However, it sounds like I should be stopping my stirring much sooner.

I've not hurt my alcohol production based on hydrometer readings, so I'm assuming its fine, but I'm curious either way what the ill effects of my stirring might have on wine production/results.

 

[Manda]

My wine goes though primary with just a towel thrown over it to keep bugs out. I stir vigorously 2-3 times a day. I stop stirring the must the day before I plan to rack to secondary to make sure most of the solids have formed a cap on the top and I can place my racking wand below in order to get juice and not fruit. I follow the same procedure out of habit even when doing a 100% juice fermentation.

 

[TonyP]

I don't know what posting you're referring to, so perhaps you can be more specific. Clearly oxygen is helpful during the fermentation process in that it helps maintain yeast vitality. Basically when there's no sugar left fermentation is over and the yeast die off (or hibernate), irrespective of whether there is oxygen in the wine.

 

[robie]

This is a highly debated subject. Lots if disagreement.

Things to consider:
Wine has been fermented to at or near dry in open vats, sometimes simple concrete vats for years and years. Still is in many places.

Many wine makers, including professionals, lock their wine down from oxygen exposure ALL DURING FERMENTATION, especially white wines. Some even do this for reds.

So which is right?

For most wine kits, we are told to move the wine from primary to secondary, where the wine is placed under an air lock, at a given SG. Consider that given SG point as the point where the experts have decided oxygen should be withheld; that's why it goes under an air lock. At that point the heavy part of fermentation is completed and has started slowing; yeast multiplying is not as important anymore.

White wines are a little more sensitive to this process, as they tend to oxidize much quicker. For this reason, they are the ones most often kept under an air lock during the whole time of fermentation.

I know successful wine makers who, once fermentation starts, never stir. There wines turn out just fine.

What I do for reds and whites. I stir daily during primary time. I loosely place the lid on top, mainly to keep critters out of the wine. A towel will work just as well for reds, buy I like a little better covering for whites. When the SG gets at or below about 1.010 (or whatever the instructions say), I either rack to a carboy and add an air lock or I leave the wine in the primary container, seal the lid and add an air lock.

In the end, whatever has been working for you, stay with it until you determine there is a problem. As you get more and more experienced, you will start seeing that little things can make a big difference in your wine; they are cumulative. At that point minor issues will be more significant and you will be better able to deal with them.

 

[dcteague]

Great responses from all, but it still doesn't quite answer the question. As I understand things, there are phases to a fermentation:

Lag - after initial pitching when they're getting used to the environment
Exponential Growth - this is when they are eating the sugar to make alcohol
Stationary Phase - fermentation slows and yeast begin to settle

It seems that during lag, they need oxygen, but in exponential, you don't want to introduce oxygen. So how can tell its gone from one stage to the next so that you stop stirring oxygen into the must? It also seems like the stationary phase is when you want to rack off the bulk solids and start your clearing process. Again, how do you know when this occurs. Is hydrometer reading able to determine this based on starting gravity?

I'm not sure if there's a way to determine this with certainty, but it seems one might see some physical evidence of the changes in fermentation.

 

[saramc]

I think Wyeast Lab does a good job explaining the phases as related to the yeast cycle during fermentation: Lag, Log, and Stationary.... http://www.wyeastlab.com/he-yeast-fundamentals.cfm
We need to remember that each yeast strain performs differently. Throw in any type of environment you expose them to & expect them to work in & the outcome is always going to vary from batch to batch, yeast to yeast, fruit to fruit, house to house. What you see, what you measure on Batch 1 will not be the same in Batch 2. There may be similarities but not an exact duplicate.
If you want to get to the nitty gritty of knowing for sure which phase your yeast are in you will need labaratory setup for cell counts and such. But keep it simple, use your hydrometer and your senses. Read about the yeast you plan to use. Work with pH/TA, nutrient balance and how all of that plays into successful fermentation. Intervene where you can.

You mention visual indicators of the phases. For me I see the fine bubbles on the surface and hear a fine sizzle. This typically occurs within 24 hours of pitching yeast, as I stir and incorporate 02 the sizzle is more audible and large bubbles break the surface, the must may foam. The reaction varies dependent upon all juice versus all fruit or a blend of. As the ferment gains speed I can actually see whirls of movement from the base of the container moving in various directions. It is cloudy. I smell the fermentation. The cap gets punched down twice a day but pops back up. Usually within 5-8 days the ferment is slowing, it may even be dry, the cap may sink on its own or may not pop back up after I punch it down. The color may be different in some way than what it was on Day 1. Sediment is dropping now. All that I described are things you can see during the ferment, but large volume containers are not typically constructed for that level of visual.

To get even deeper in terms of stirring you also have to consider sur lie and bâtonnage (lees contact and stirring) & what that can bring to the table. Good overview here: http://www.brsquared.org/wine/Articles/surlie/surlie.htm

Sorry if I am off base in my response, but I hope it helped...even one person.

 

[Elmer]

I dont stir until the SG hits about 1.4
At this point I have skipped the 1st racking to a carboy (find getting the must into the carboy too much of a pain), instead I add some yeast nutrient and stir the heck out of it every day!

I am most likely wrong and prepared to be flamed!

 

[dcteague]

saramc - thanks. This is what I was hoping for in a response. I figured there was really no precise way of knowing when one phase starts and another ends, but figured there might be some evidence and your info helps.

The write-up you posted on the sur lie process is also very interesting. At the end of all of this debate, it all seems to boil down to your preference based on your own outcomes (with a little science to inform you along the way).

Thanks to all for great responses....

 

[TravelingTea]

I think Wyeast Lab does a good job explaining the phases as related to the yeast cycle during fermentation: Lag, Log, and Stationary.... http://www.wyeastlab.com/he-yeast-fundamentals.cfm
We need to remember that each yeast strain performs differently. Throw in any type of environment you expose them to & expect them to work in & the outcome is always going to vary from batch to batch, yeast to yeast, fruit to fruit, house to house. What you see, what you measure on Batch 1 will not be the same in Batch 2. There may be similarities but not an exact duplicate.
If you want to get to the nitty gritty of knowing for sure which phase your yeast are in you will need labaratory setup for cell counts and such. But keep it simple, use your hydrometer and your senses. Read about the yeast you plan to use. Work with pH/TA, nutrient balance and how all of that plays into successful fermentation. Intervene where you can.

You mention visual indicators of the phases. For me I see the fine bubbles on the surface and hear a fine sizzle. This typically occurs within 24 hours of pitching yeast, as I stir and incorporate 02 the sizzle is more audible and large bubbles break the surface, the must may foam. The reaction varies dependent upon all juice versus all fruit or a blend of. As the ferment gains speed I can actually see whirls of movement from the base of the container moving in various directions. It is cloudy. I smell the fermentation. The cap gets punched down twice a day but pops back up. Usually within 5-8 days the ferment is slowing, it may even be dry, the cap may sink on its own or may not pop back up after I punch it down. The color may be different in some way than what it was on Day 1. Sediment is dropping now. All that I described are things you can see during the ferment, but large volume containers are not typically constructed for that level of visual.

To get even deeper in terms of stirring you also have to consider sur lie and bâtonnage (lees contact and stirring) & what that can bring to the table. Good overview here: http://www.brsquared.org/wine/Articles/surlie/surlie.htm

Sorry if I am off base in my response, but I hope it helped...even one person.

This is exactly what I was looking for. My wine is sizzling and I wanted to double check and make sure that was a sign of a good fermentation.