WorkSpace said:
Hello from down-under :wave: . This is my first post here, and I haven't made mead before. So I have been reading the newbee guide and some relevant threads. As an extract beer, wine and spirit wash brewer, I have been trying to make sense of the process. Two aspects of it seem odd to me, and maybe you could explain what I am missing.
WELCOME TO GOT MEAD?!
WorkSpace said:
I am trying to understand why it should be necessary to heat the must. I understand that this is done to get rid of natural yeasts and micro-organisms. But I would have thought that honey is pretty clean stuff. We have jars of it that has been sitting on the shelves for years, and it is still fine. What happens if the must isn't heated. Has anyone done both and compared results?
Heresy! Not heating the must???? Are you mad man???? LOL
J/K LOL - In fact you'll find most of us here don't heat their must in part because honey is indeed very clean (inherently very bacteriostatic due to the low amount of water) but more because when you heat honey you cook off the enzymes, proteins and delicate floral characters and other volatile aromas that translate more complexity and flavor into your mead.
WorkSpace said:
The other thing I couldn't understand was aeration during the fermentation process. Is this really necessary? With all the beer, wine and spirit washes I have made, I have never done this. After pitching the rehydrated yeast, the fermenter is closed up, the airlock is fitted and it is left alone for about a month (depending on temperature). I know aeration is done to promote yeast growth. But wouldn't it be better to ensure that adequate yeast is available before fermentation starts? I would have thought that interfering with the fermentation process would be counter-productive.
Actually the reason that we aerate is to not only promote yeast growth, but because as generations of new yeast are produced during fermentation, those new generations need a constant supply of oxygen in order to form strong cell walls with other components (sterols, etc.) and keep the cell wall supple and flexible. If the cells do not get adequate supplies of oxygen and nutrient the cell walls will become brittle and they will not form enough strength to regulate osmotic pressure and will undergo premature autolysis. During that time before they do die off they will be stressed from lack of oxygen and nutrient and produce off flavors. When you see a mead fermentation that lasts more than a couple of weeks what you're seeing in many cases is an under aerated and nutrient deprived fermentation.
From a recent SO2 in Wine lab report I did:
...
snip...
Molecular oxygen serves as a micronutrient for many organisms, required for the biosynthesis or degradation of many compounds. PPO successfully competes with the microbes present in wine for O2. Oxygen is required by the yeast for optimal ethanol tolerance (this is why we aerate in order to get O2 into the must for the yeast so they can synthesize sterols to strengthen the cell walls and have a higher ETOH tolerance), if PPO activity is unchecked, the yeast may be in a nutrient deficient situation (in this case O2 as a nutrient). This is an additional reason to add SO2 in grape musts. It is not clear at the molecular level exactly how SO2 is able to inhibit PPO activity....
snip...
OK, we're dealing with honey vs grape must here and the rate of aeration and stages of aeration are going to be different. With grapes you're dealing specifically with a couple of anti-oxidants that will compete with with yeast for oxygen as the skins are in contact with the juice (most specifically PPO - Polyphenoloxidase) While you don't have that in honey must, you do have higher osmotic pressure so a couple of aerations daily during the first 1/3 of the ferment is beneficial (in order to build strong cell walls) and will not present risk of oxidation because the oxygen is being stripped from the yeast cells by the rapid production of CO2.
From Dr. Clayton Cone of Lallemand:
Yeast need a trace amount of oxygen in an anaerobic fermentation such as meadmaking, winemaking and brewing to produce lipids in the cell wall. With out O2 the cell cannot metabolize the squalene to the next step which is a lipid. The lipids make the cell wall elastic and fluid. This allows the mother cell to produce babies, buds, in the early part of the fermentation and keeps the cell wall fluid as the alcohol level increases. With out lipids the cell wall becomes leathery and prevents bud from being formed at the beginning of the fermentation and slows down the sugar from transporting into the cell and prevents the alcohol from transporting out of the cell near the end of the fermentation. The alcohol level builds up inside the cell and becomes toxic then deadly. Lallemand packs the maximum amount of lipids into the cell wall that is possible during the aerobic production of the yeast at the factory. When you inoculate this yeast into your must, the yeast can double about three time before it runs out of lipids and the growth will stop. There is about 5% lipids in the dry yeast.
In a very general view:
At each doubling it will split the lipids with out making more lipids (no O2). The first split leaves 2.5% for each daughter cell. The second split leaves 1.25% for each daughter cell. The next split leaves 0.63%. This is the low level that stops yeast multiplication. Unless you add O2 the reproduction will stop. When you produce 3-5% alcohol beverage this is no problem. It is when you produce higher alcohol beverage or inoculate at a lower rate, that you need to add O2 to produce more yeast and for alcohol tolerance near the end of fermentation. You definitely need added O2 when you reuse the yeast for the next inoculum.
Dr. Clayton Cone
References:
Texts:
Bisson, L., 2005. VEN 124 Wine Production for Distance Learners, Lesson 5: Juice and Must Treatments and Additions Topic 5.2: Juice Additions
Boulton, R., V. Singleton, L. Bisson, and R. Kunkee. 1996. Principles and Practice of Winemaking. Chapman and Hall. New York
Peynaud, Emile, 1984. Knowing and Making Wine, (English Translation) John Wiley and Sons, Inc. USA
Journal Articles:
Baldwin, G., Basic Effects of Sulfur Dioxide on Yeast Growth. American Journal of Enology & Viticulture Volume 2: 45–53. 1951
Cocolin, L., and D.A. Mills Wine Yeast Inhibition by Sulfur Dioxide: A Comparison of Culture-Dependent and Independent Methods. Am. J. Enol. Vit. 54: 125 – 130. 2003
Other Articles:
Delteil, D., Enological yeast effect on the sulfur dioxide content and management in wines. Institut Cooperatif du Vin, 1 – 4 1992
WorkSpace said:
Introducing air slows fermentation, and opening the fermenter increases the risk of contamination. What happens if you don't aerate?
Introduction of air does not slow fermentation. Opening the fermenter does indeed increase the risk of contamination, but with proper aseptic technique that possibility is heavily mitigated. If you don't aerate you'll run into issues as outlined above.
WorkSpace said:
I hope this doesn't sound too argumentative. I just need to understand why things have to be done. ???
Not at all, they're good questions. I hope my answers will help you decide to try something different and compare your results in a blind tasting with friends and other mead makers.
Cheers,
Oskaar