Industrial fermentation tanks are multi-storied structures. When I visit commercial breweries, I often wonder, whether they build the tank first and construct the whole factory around it or vice versa. The amount of CO2 emitted by these large tanks is so large that one whiff of the fermenting tanks can leave us dizzy due to lack of oxygen. Home brewing, unfortunately, suffers from high surface area to volume ration. This is the reason why the prevention of degradation due to oxygen contact becomes so important.
Oxygen oxidizes alcohol into acetic acid, making it too sour for consumption. That’s why all recipes of wine and beer would mandate fermentation and age under an airlock. The goal is to vent off all CO2 produced due to yeast activity and yet prevent O2 from entering and ruining the batch.
Airlock (armed on right)
You can pick either of the airlocks: S type (left) or 3 pieces (right) to get the desired result. Load the airlock with some water (usually alcoholic spirit or a disinfectant). This forms a barrier through which the build-up CO2 is released without allowing the air from outside to enter inside, causing oxidation.
For bulk aging of wines, it is recommended to check for airlock water level every week to 10 days and replenish for evaporation loss. Another advantage of the airlock is that they keep the fruit flies at bay. A lot of fruit flies are attracted to the CO2 produced during fermentation and hover around the open fermentation vats (in the first week of winemaking).
Siphon: Pouring the wines/beers from one vessel to another (for transfer to secondary fermenter or bottle) is not recommended. As pouring causes the air to mix with the beverage. The method followed widely is siphoning the liquids as illustrated in the diagram.
This is a simple gravitational method where the water flows inside a pipe and hence shielded from oxygen contact. The CO2 being heavier creates a blanket that prevents oxygen to come in. Even after the fermentation is over, the primary fermenter has some residual CO2 to create this shield. Industrial breweries use a CO2 purge to flush out oxygen by releasing some pressurized CO2 in the tank before pouring the liquid for aging or secondary fermentation.
Use a pump (or syringe) to start the flow in the siphon (via suction) rather than sucking the air through our mouth. Human saliva can cause contamination and also is unsanitary.
I use a three-level approach in my fermentation. The primary happens on top of the refrigerator (about 6 feet high), the secondary vessel is kept on top of my kitchen slab or table height (about three feet high) and the final bottles are on the floor.
A fellow hobbyist with fragile glass fermenters often uses a vacuum pump technique. They create a vacuum in the secondary, which can start the transfer from primary to secondary. This has three advantages:
- There is no need to move or lift fermenters around. All equipment can be at the same level and vacuum can suck out the juices.
- The vacuum sucks all O2 out. Which eliminates any oxidation chance in the secondary vessel
- This also facilitates a rapid de-gassing which is beneficial if we are planning to serve fresh wine which is less than a month old and is tart because of carbolic acid (dissolved CO2).
Conical fermenters are a boom to the most advanced home brewers. Firstly, it allows for the timely removal of dead yeast (the cake at the bottom of the fermentation. The autolysis of dead yeast can introduce a lot of off-flavors). This means that by just emptying out the dead yeast, we can use the same tank for primary and secondary fermentation without having to transfer the fluids and risk oxidation during the pumping.
For larger than 50 liters in tank size, industrial glycol jacketed cooling system is recommended to maintain a controlled fermentation rate. For smaller conical fermenters, an old refrigerator or an ice-cream chest freezer or air conditioner with the thermostat is ideal. Lagers brewers need refrigerant even to make a small batch. Hence they use a conical fermenter. Lagers take 60-90 days to ferment and mature and without the professional setup, one will not be able to control temperatures, oxidation, and other parameters with a simpler setup.
Headspace is the air trapped between the lid and the water level in the fermenter. Every time we open, this area gets filled with Oxygen and ruin the batch. Making headspace zero is a bad idea, as fermentation causes the brew to rising and spillover. Having too much headspace means that every time the lid is opened (for transferring, bottling, infusing spices, or taking a reading) the batch gets oxidized more and more. Two to three fingers width of the gap is optimal.
If the must or wort is more than the fermenter size, we can always use a small glass container, attach an airlock and divide the liquid. If it is too less, we need to insert inert glass marbles balls (kanche). Just like the crow and water pitcher story that we heard growing up. These stone-like glass balls will help reduce the headspace.
Another source of oxidation is the bottling process. Pouring beer/ wine using a funnel agitates them and causes oxygen to get dissolved. A better approach is to use a bottling wand. This essentially is a spring-loaded valve at the base of a stainless steel pipe. When the valve is pressed, the liquid starts to flow and after the bottle is filled, lift the pipe. The valve ensures that there is no spillage in the process. The negative displacement due to the removal of the tube will help in establishing a uniform water level in all bottles and gives a professional look as well.
Mild micro-oxidation (as through a porous cork) is desirable as it can introduce nutty, almond-like notes in wines. Too much oxidation (esp. due to lack of proper equipment, bottling and storage) is the reason why so many of the amateur home brew taste stale, winy/ vinous, cardboard, papery, or sherry-like aromas and flavors. It is usually caused by exposure of beers to oxygen at high temperatures. In the case of wines, it could even result in a change in color from red to orange. The use of proper equipment, processes and temperature control during aging is all that is needed to overcome this beast.
The above discussions should give a good idea to home-brewers about the ways to eliminate most of the sources of oxidation. Temperature and sunlight are two other aspects that one needs to be wary of. However, for an educated soul, a bit of precaution and common sense is all that is needed to make the perfect batch.