Pressure Fermenting Mead and Wine

Why this is worth knowing

Nobody writes about it

Pressure fermentation is thoroughly covered for beer and almost entirely absent from mead and wine content. That is a gap rather than a verdict: the technique works for both, and for mead in particular the benefits line up unusually well with the problems mead actually has.

The mechanism is the same as in beer -- see pressure fermentation explained -- but the reasons to do it are different, which is the point of this page.

Benefit one

Fusel suppression, which mead needs most

Elevated dissolved CO2 suppresses the yeast metabolic pathways that produce esters and fusel alcohols. In beer that is used to ferment lagers clean at warm temperatures.

In mead it addresses the category’s signature fault. Honey is nearly devoid of nitrogen, so mead yeast is prone to stress, and stressed yeast throws fusel alcohols -- the hot, solvent-like harshness that is the whole reason mead is said to need a year. Pressure suppresses exactly those compounds.

Important caveat: this does not replace a nutrient schedule. Pressure masks a symptom of malnourished yeast; it does not nourish the yeast. Do both -- stagger your nutrient properly per your first mead, step by step -- and the pressure is a belt alongside the braces.

Benefit two

Oxygen exclusion, which matters more here than in beer

This is the stronger argument, and it is specific to these beverages.

A beer ferments for two or three weeks and gets packaged. A mead or wine ferments for two to four weeks and then ages for months. Across that span oxygen is the dominant threat: it dulls honey character, browns whites, and eventually produces sherry-like oxidation. Every exposure counts more because there is more time for the damage to accumulate.

• A sealed pressurized vessel cannot draw air in. An airlocked vessel does, every time the temperature drops -- the contracting liquid pulls room air and airlock sanitizer back through the airlock.
• Closed transfer to the aging vessel. This is the big one. Instead of siphoning through air into a carboy, you push the mead or wine across under CO2. Starting a nine-month age with less dissolved oxygen is worth real money.
• The headspace is CO2, not air, for the whole fermentation.

What it does not do

Three honest limits

It does not carbonate your wine, usefully. In beer, partial carbonation at transfer is a benefit. For a still wine or a still mead it is something you then have to remove, which means degassing. If you want a sparkling mead it is an advantage; otherwise vent the vessel down before transferring and expect to degas.

It does not fix headspace during aging. Pressure helps during fermentation. Once the mead is in its aging vessel for nine months, the vessel’s geometry and fill level are what matter -- see best mead fermenters and best wine fermenters.

It does not suit every style. As in beer, pressure suppresses yeast expression. For a traditional mead where you want the honey and the yeast character to show, or a wine where varietal character is the point, heavy pressure flattens things you wanted. Keep to 10 to 12 psi rather than 15 for these.

How to do it

The practical sequence

1. Use a rated vessel. A FermZilla with its pressure kit, a KegMenter, or a rated conical. Never an unrated vessel -- best pressure fermenters.
2. Aerate the must thoroughly and pitch yeast with the first nutrient dose.
3. Leave it vented for 12 to 24 hours so the growth phase is unrestricted.
4. Set the spunding valve to 10 to 12 psi. Lower than a beer, because yeast expression matters more here and you do not want the carbonation.
5. Add nutrient on schedule. This means venting and opening, which is the one practical awkwardness of pressure fermenting a mead. Vent fully before opening.
6. When fermentation finishes, vent down and do a closed transfer to the aging vessel under low pressure.