Oxygen: Yeast needs oxygen to jumpstart fermentation and this is why it is important to aerate your mash before fermentation. You can aerate your mash by pouring it from one bucket to another about 12 times or picking up your bucket and shaking it for about 60 seconds.
Once you put it to ferment leave it alone to do it's thing. If you shake it or stir it and introduce o2 you only slow it down. Leave it be, when the bubbles stop it's done.
It's not recommended to stir the mash after adding the yeast, especially after fermentation has begun. There are risks of contamination by bacteria or oxygen. It could also cause the yeast to clump together, and the beer would not ferment properly.
The yeast need this oxygen to grow and to produce important cell wall constituents. It is important to introduce enough oxygen into wort at the beginning of fermentation. Shaking the fermenter will, at best, add about half the recommended level of 10 parts per million oxygen into solution.
Once you add the yeast you will want to stir the fermenting wine must around as much as you can. The goal is to not allow any of the pulp to become too dry during the fermentation. Stirring it around once or twice a day should be sufficient.
The fermenting container should not be metal or have scratches or cracks which could harbor harmful bacteria. Some metal containers (other than stainless steel) may react with the acid in the food and give it a strange flavor or color and could leach into the food.
Trying an Open Fermentation
As soon as you notice fermentation starting to slow down rack into a carboy and put the airlock in place. Your fermenter should only be open during “primary” fermentation which is when the first 70% or so of your sugars are fermented (here's more on Primary vs Secondary Fermentation).
The most common causes are: Dead (not vital) or unhealthy (not viable) yeast cells. Too little yeast pitched. Too much yeast pitched, causing excessive krausening and loss of healthy yeast through blow off. Not enough nutrients in the wort to sustain yeast activity.
Temperature, pH, aeration, substrate concentration, and nutrient availability all influence the fermentation process and metabolic processes.
Generally speaking, wine can't ferment for too long. The worse that can happen is a “miscommunication” between the sugar and the yeast due to either using the wrong type of yeast or fermenting under the wrong temperature. Even if this happens, you can still salvage most if not all wines.
So in the end I guess the answer to the question: “can I add sugar during fermentation?”, is yes you can. With the only side note being “but it only makes sense if you are making a high alcohol wine”.
No, you do not need an airlock, but you need some way of releasing the CO2 as the mash is fermenting. The airlock has a cap with little pinholes, the carbon dioxide escapes and prevents bugs from entering the airlock.
You most definitely can bulk ferment sourdough too long. If you leave the dough to ferment for too long, it will become "over fermented". Over fermented dough will lose its structure and become a soupy, sloppy mess that you will not be able to shape.
Burping is essentially just opening your bottles ever so slightly during the second fermentation process to release air or “excess pressure” in the bottle. Many brewers recommend burping bottles every day, or every other day while your bottles are fermenting at room temperature.
If there are still bubbles in the airlock after 14 days let it sit for another few days, or at least until there is no bubbling for at least a minute or two. Once there is no activity in the airlock, fermentation is complete.
Fermentation times can be shortened by using powdery (non-flocculent) strains of yeast or by mechanically stirring the fermenting wort. The yeast can also be roused toward the end of fermentation by the injection of carbon dioxide or by using a re-circulating device.
Temperature, pH, acidity, ethanol, sulfite and availability of nutrients are all important for the growth and metabolic activities of the lactic acid bacteria. The lactic acid bacteria are more fastidious in their growth requirements than the yeast.
If too much sugar still appears to be the only problem, you can try adding 3 or 4 packs of Red Star Pasture Champagne Yeast to the batch. This won't be two much wine yeast since the pack you added before multiplied itself to about 150 times the original amount.
If the airlock is not bubbling, it may be due to a poor seal between the lid and the bucket or leaks around the grommet. Fermentation may be taking place but the CO2 is not coming out through the airlock. This can also be caused by adding too much water to the airlock.
You can tell if your fermentation is stuck if you notice no activity in your airlock and no layer of Krausen in the wort. A lack of changes in the hydrometer reading three days after the start of fermentation and a high amount of sugar in the brew is another tell-tale sign.
Leaving the lid and airlock off will allow the primary fermentation to start sooner and continue more rapidly, but it can also leave the fermentation susceptible to contamination should it not start in a timely fashion.
That being said, a general guideline is usually 2-3 weeks for primary fermentation followed by several weeks or even months of cold conditioning/lagering in a secondary vessel. The whole process takes about 2-3 months, depending on the style. This article dives into more details on lager fermentation.
Is a Fermentation Airlock Necessary? Some types of fermentation require airlocks and others don't. For most types of homebrewing, distilling, or fermenting, people tend to use airlocks. Airlocks provide a few key benefits to the fermenter.