School me in wine biology

[forces]

After recently screwing up a the fermentation on a batch of mead, I started reading on wine making and stumbled across this article

So, my issue/ question with this article is that he says to pitch the yeast (after 24 hours of cooling) and just set a towel or something over the fermenter for the first several days, then rack to secondary and add an airlock. In another section the guy says that you will rack to secondary when your gravity reaches 1.030-1.040. Is this a normal procedure for mead/ wine? 'Cause I can't make sense of it

School me in biology please:

So my limited knowledge of biology and fermentation says that if when glucose sugar is metabolized, it first goes through glycolysis and is broken into 3-carbon pyruvate. Then the pyruvate is either metabolized aerobically or anaerobically. If it is fermented anaerobically (like most of us beer guys do exclusively except when making a starter*) then the pyruvate is broken into ethyl alcohol and CO2. However, if it is metabolized aerobically (in the presence of oxygen) it will go through the Kreb's cycle and create CO2 and water... And if you started out at say, 1.095 and fermented aerobically (without and airlock) down to 1.040 then you would have created a very watery solution devoid of alcohol, and with only 1.040 residual sugar, you would only have enough sugar left to make a wine with an ABV of roughly 3-4 %.

Here's my issue

A 4% wine is rare... really anything less than about 9-10% is relatively uncommon, even for whites. I understand the need for yeast cells to reproduce in order to eat all of the sugar in the must, but letting it eat half the sugar before even starting fermentation seems strange to me. Am I missing something, or is this aerobic fermentation method not commonly used?

Using a little chemistry here in a hypothetical:
A. you have 10.5 # glucose in 5 gallons of water = 1.097 SG (according to beer smith)
B. It ferments partially to 1.039 SG = 4.25 # glucose in 5 gallons of water left to go around
C. 1.039 OG to 1.000 FG fermentation = roughly 3.5 % abv.

6.25 # were metabolized aerobically above, this would yeild about 1700 grams of water produced from the sugar, which is just less than a half gallon of water.

 

[Nateo]

If the must is properly aerated, or even better, oxygenated, then an airlock during primary should be fine.

The O2 solubility of must isn't very good at high gravity. Air doesn't have very much O2 in it. So even if the top of your must is exposed to air, not very much O2 will actually make it into solution. The only time you'd have a prolonged aerobic fermentation would be if you added O2 every day for like a week.

I would say the number one reason for poor fermentation is lack of pH monitoring and correction when necessary, yet that doesn't even make that list.

 

[forces]

Thanks for the explanation. That makes sense... So even in open-vat fermentation, it isn't necessarily 100% aerobic respiration. More questions ahead:

1.Do any of the wine makers on this forum use this technique?

If so, how long do you ferment "open" before adding an airlock? and do you rack to secondary THEN airlock, or just install the thing, and go to secondary when you've hit your desired FG?

2. Is there anyway then to accurately determine ABV? (ie; is there any way to know how much water you've created vs. alcohol?) It would seem to me that final gravity wouldn't be a great determinate of alcohol percentage, because both the water and alcohol produced are less dense than the aqueous sugar from which they were created.

Thanks again for the help

 

[Yooper]

I cover my primary with a clean towel to keep out fruitflies. It makes it much easier to stir daily (or twice a day) when I need to. Once fermentation slows down, at about 1.020-1.010, that's when it is moved to a carboy and airlocked, as the co2 production slows down and can no longer dependably protect the wine from oxidation.

I don't know how much "water" is actually produced and present in the wine. I doubt much at all. Very little is actually metabolized aerobically (as oxygen update only occurs during yeast reproductive phase and not during fermentation), and ethanol production is an anaerobic activity, so I just use the old standard (OG-FG) x 131= approx. ABV and it's close enough for me. Alcohol is produced by the yeast anaerobically and the waste product is c02, not water. Saccharomyces cerevisiae prefer fermentation to respiration. These yeasts will produce ethanol even under aerobic conditions given the right sources of nutrition.

 

[Nateo]

Learning about winemaking teaches you a ton about fermentation. Yeast health and fermentation management are what winemaking is all about. Winemakers know yeast way better than beer guys. Beer brewers know sanitation really well, and seem to be much more interested in fermentation temperature control. The strange is they don't generally talk to each other, even though they use the same bug.

If you can combine the two knowledge bases, there's nothing you can't ferment well.

 

[forces]

Learning about winemaking teaches you a ton about fermentation.

I'm finding that to be true after just a day and a half of poking around the internet periodically.

It seems like this open-fermentation is kind of like using your must as a starter (producing lots of yeast cells in the presence of O2). Is there a reason why wine makers don't just use liquid yeast and starters to get the # of yeast cells required to ferment the batch?

 

[forces]

I cover my primary with a clean towel to keep out fruitflies. It makes it much easier to stir daily (or twice a day) when I need to. Once fermentation slows down, at about 1.020-1.010, that's when it is moved to a carboy and airlocked, as the co2 production slows down and can no longer dependably protect the wine from oxidation..

Anyone know if this is appropriate for fermentation of mead??

 

[Sardoman]

Fermentation: Sugar used anaerobically to generate energy. CO2 and ethanol are the biproducts.

Respiration: Sugar and O2 used to fuel the generation of lots more energy per sugar molecule than with fermentation.

Yeasts used for fermentation, including beer, wine and baking yeasts prefer to ferment, and will do so simultaneously as they respire in an oxygen-rich environment. This is not necessarily true for other yeasts, such as most laboratory strains of S. cerevisiae. It is thought that the fermentation yeasts might have developed the tendency to ferment simultaneously with respiration, even at a cost of lower energy generation efficiency, in order to rapidly deplete their environment of simple sugars, thus outcompeting other microbes and making a niche for themselves. They could then reverse the fermentation process at their leisure, utilizing the ethanol as a source for respiration. No, yeasts used for fermentation can't utilize ethanol, but many wild yeasts and laboratory yeasts can.

You can use liquid yeast for wine. White labs carries several strains. I imagine you could make starters as well.

 

[Nateo]

My WAG about the lack of starters with wine fermentations is that there are different philosophies concerning fermentation. Picture fermentation like a battle. Beer guys want to pitch a bunch of active yeast to plow through the sugar. The yeast wins with sheer numbers and brute force. Wine guys start with smaller numbers of yeast, but the fermentation is more carefully controlled. So it's more like small units with superior tactics.

 

[pdxal]

Wine is also full of simple sugars to metabolize, and beer is only partially full of them, with lots of more complex sugars like maltose to metabolize.

 

[Nateo]

Wine is also full of simple sugars to metabolize, and beer is only partially full of them, with lots of more complex sugars like maltose to metabolize.

Wort composition:
http://hbd.org/brewery/library/EnzStuckFermAW1095.html

I think it's interesting that certain wine strains can metabolize maltose and maltotriose, while some ale strains cannot metabolize, or can only partially metabolize maltotriose. Lager strains generally can metabolize maltotrios.