Questions from a Beginner

[NuMu436]

The first question is a bit scientific:
Why do the pros encourage "degasing" during the first few days of fermentation?
This confuses me from a biochemical standpoint, because I understand fermentation to be the anaerobic (oxygen-lacking) metabolic process that produces ethanol as a side product in unicellular organisms (yeast in this case). By degasing, the meadmaker stirs in oxygen to release carbon dioxide. It just seems to me that adding oxygen takes away from that ethanol production, regardless of whether carbon dioxide is unhealthy for the yeast.

Second:
How do you calculate Final Gravity? Is it completely dependent on Original Gravity?
I see a lot in FAQs about doing X at 50% sugar depletion, doing Y at Z% sugar depletion (mostly talking about Staggered Nutrient Addition). I need a way to predict the Final Gravity in order to figure out where those depletion points are. My first batch OG was 1.136.

Third:
Is it possible to mix a large container of sanitizing solution and store for long periods of time?
My local supply vendor told me today that it isn't possible, but honestly I want to make sure he wasn't just encouraging me to be wasteful so I have to come back to buy more.

Thanks!

Jay S.

 

[cyberlord]

During the initial phase of yeast activity the yeast are multiplying at an incredible rate and that phase of activity requires oxygen. If the must is full of CO2 then the must can't contain O2. So the CO2 is degassed to allow more O2 into the must so the yeast can multiply.

Final gravity is measured just like OG. Then you can mathematically calculate the approximate alcohol content of the finished product using the OG and FG values.

Yes, I make a gallon of Star San and keep it for a bout a month. I am a proponent of the spray bottle method as it wastes little and you don't need a dipping container.

 

[biochemedic]

1) cyberlord notes the need for oxygen during the initial phases of yeast reproduction, which is indeed aerobic. This is why aeration, and preferably actual oxygenation, of the must is important at the time of pitching. There is probably also benefit to a second addition of oxygen sometime in the first 12-24 hrs after pitching. Once active fermentation starts and CO2 is more actively being produced, it is beneficial to remove it to assist in keeping the pH from dropping, which can be toxic for the yeast. Additionally, CO2 itself at higher concentrations can be directly yeast toxic. As I understand it, it has nothing to do with allowing more oxygen in, nor are you "replacing" CO2 with oxygen while degassing. In fact, you can degas without even opening your carboy...I use a blow off tube, and basically just swirl/shake the $h!t out of the carboy every time I go near it...

2) Predicting your FG so you can determine where various break points are for nutrient addition is at best a guess. If your expected ABV at dry is well above your yeast's tolerance than you can just use 1.000 as an endpoint (realizing that truly dry is actually somewhere between 0.990 and 1.000) The real trick comes when you're starting with a really high OG, and expect that you might peter out somewhere with some residual sugar left. Yeast don't know they have a rated tolerance, and in your brewery a given yeast might go from 1.136 to 1.020. In mine, it might get to 1.010 or only reach 1.035. For this reason (plus, I'll admit it, because of a bit of laziness) I just do my SNA's at time of brewing/pitching, shortly after real active fermentation/krausen starts, and then about a day or so later.

3) Star San indeed keeps well...if you're concerned, you can get cheap pH test strips, and check to see that the pH is still below 3.0 I mix Star San 5 gal at a time in my bottling bucket, and keep it in cleaned out milk jugs.