Mead is stabilized for several reasons. A stable mead will not restart fermentation. This allows it to be safely packaged and to maintain flavor consistency. This also allows the meadmaker to back sweeten the mead if desired. Lastly, stabilized mead is more resistant to degradation and infection.
Mead should be stabilized once fermentation is complete and the mead has begun to clear. You don't have to wait for it to clear completely (as that may cause you to need to wait for it to clear again), but trying to stabilize mead too early can curtail the final stages of fermentation when yeast are cleaning up after themselves.
Stabilization may happen naturally (see below). For some meads it can be beneficial, though unnecessary - for example a normal strength mead that is completely dry.
Always confirm that your mead is stable before storing in sealed vessels or packaging. Confirm this by taking gravity readings after back sweetening and a week or so afterwards.
There are two chemical additives widely used together to stabilize mead: potassium metabisulfite and potassium sorbate. In summary, potassium metabisulfite (k-meta) removes oxygen, resulting in a severely lower yeast population that can reestablish fermentation in time; potassium sorbate (k-sorb) effectively sterilizes any remaining yeast so they cannot reproduce. Together they are very effective at preventing further fermentation, but probably not effective at completely stopping a healthy fermentation.
When back sweetening, you may wish to wait 24 hours after adding stabilizers to add the additional sugar. Fermentation has been known to restart when racking a mead with residual sugar.
Potassium metabisulfite and potassium sorbate should be used only when the mead has fermented dry or fermentation has stopped for other reasons (cold crashing, or the yeast reaching alcohol tolerance). Confirm that a fermentation has stopped by taking two hydrometer readings a week apart. If they are not the same, fermentation is still ongoing and chemical stabilization will not reliably prevent refermentation.
Both chemicals will typically be used, but potassium sorbate may not be useful above 14-15% ABV.
AKA: PM, K-Meta, Campden Tablets
This is widely used in meadmaking to remove excess free oxygen from an aging mead. As an antioxidant, it helps to protect color and flavor during long aging. The lack of oxygen also causes much of the yeast population - but not all, keep reading - to die off, especially if they are already struggling. It's available to the homebrewer in two main forms: Campden Tablets and powdered potassium metabisulfite.
Potassium metabisulfite breaks down, dissipates, and loses effectiveness within a few hours of dosing. It was once common to add a dose at every racking to minimize oxygen exposure. Some recipes also call for its use prior to pitch to remove oxygen for the purpose of tamping down the population of any unwanted microogranisms, giving the yeast a big head start out-competing them for resources.
Campden Tablets are widely available at any homebrew shop. Think of Campden Tablets as a pre-measured easy-to-use form of potassium metabisulfite. Since this substance is used in very small quantities and by weight, the tablets are useful if you don't have an accurate gram scale. A campden tablet provides .44 grams of potassium metabisulfite. You may find Campden Tablets that are made with sodium metabisulfite. Check the packaging carefully and avoid these. They work the same, but will leave sodium in your mead instead of potassium, which may affect the flavor in undesirable ways. Campden Tablet packaging recommends 1 tablet per gallon to stabilize mead.
You can also buy potassium metabisulfite in a pure, powdered form. This is useful if you have a gram scale with at least .1 gram accuracy. This is great for very accurate additions, but be careful when using it, and don't breath the dust. Packaging usually suggests that about 1/4 teaspoon will treat 6 gallons of mead (and add 50-75 PPM of free sulfites - keep reading).
So how does it work? When dissolved in water, potassium metabisulfite breaks down into three sulfuric compounds: sulfite, bisulfite, and sulfur dioxide (SO2). Each of these compounds is capable of binding with oxygen molecules which prevents those molecules from oxidizing the mead or being used by yeast and spoilage organisms. These free sulfites are also capable of binding with other molecules or even evaporating out as gas, which can complicate the dosage. You also need to know that 57% of potassium metabisulfite is free SO2. The rest is already bound or otherwise unusable.
The package-recommended dosage is acceptable but probably excessive. Some people report sensitivity to high sulfite content. Excessive dosing can also add a noticeable bite that can take months to age out. To minimize or avoid these problems, we can tailor the amount of added free SO2 to the specific needs of the mead. To do this, we need to know the pH of the mead after fermentation is complete, and the free SO2 already present in the mead. Note that if you intend to back sweeten after stabilization, you may need to re-check the pH and adjust the SO2 upward again. If you add honey (pH 3.5-6.0) as a sweetener to a mead that had a pH of 2.9, this may change the final mead's pH enough to require more free SO2.
If you cannot check your pH and free SO2, you can use what the packaging recommends or adjust it downward based upon whatever information you do have.
Testing pH is the simpler of the two. Test strips are widely available at most homebrew shops or even the aquarium section of your nearest big box store, but they are not precise. A electronic pH meter is far more accurate but also much more expensive.
There are test kits to detect free SO2. Accuvin makes one of these and provides the following chart for free SO2 ranges based upon pH.
| pH | Target Free SO2 (PPM or mg/L) | K-Meta (grams/5 gallons) † | K-Meta (grams/gallon) † | Campden Tablets per 5 gallons (roughly)‡ |
|---|---|---|---|---|
| 2.9 | 7-11 | .23-.37 | .05-.07 | .5 - 1 |
| 3.0 | 8-13 | .27-.43 | .05-.09 | .5 - 1 |
| 3.1 | 10-16 | .33-.53 | .07-.11 | 1 |
| 3.2 | 13-21 | .43-.70 | .09-.14 | 1 - 1.5 |
| 3.3 | 16-26 | .53-.86 | .11-.17 | 1.5 - 2 |
| 3.4 | 20-32 | .66-1.06 | .13-.21 | 1.5 - 2.5 |
| 3.5 | 25-39 | .83-1.29 | .17-.26 | 2 - 3 |
| 3.6 | 31-49 | 1.03-1.63 | .21-.33 | 2.5 - 3.5 |
| 3.7 | 39-63 | 1.29-2.09 | .26-.42 | 3 - 4.5 |
| 3.8 | 49-79 | 1.63-2.62 | .33-.52 | 3.5 - 6 |
| 3.9 | 62-98 | 2.06-3.25 | .41-.65 | 4.5 - 7.5 |
| 4.0 | 78-123 | 2.59-4.08 | .52-.82 | 6 - 9 |
† Assumes 0 pre-existing free SO2.
‡ Divided the values from Required K-Meta column by .44 and rounded to nearest .5.
A finished dry mead's pH is often below 3.2. 3.5 and below is fairly typical for a sweet mead. As you can see, most meads will need far less than 1 tablet per gallon or 50-75 PPM (same as mg/Liter) free SO2 provided by 1/4 teaspoon of potassium metabisulfite powder.
If you're able to test for free SO2 and pH before adding potassium metabisulfite, use the following formula to determine how many grams of potassium metabisulfite to add.
( (gallons of product) x (3.785) x (required free SO2 PPM) ) / (1000 mg/g) x 0.57) = grams of Potassium Metabisulfite
When physically adding campden tablets, crush them into a powder with a spoon to make them easier to dissolve. Once you have a powder or if you're starting with pure potassium metabisulfite powder, take a small sample of mead, then dissolve the powder thoroughly. Add this sample back to the fermenter and gently but thoroughly mix it back in. If you are racking at the same time as stabilizing, you can add your powder to the bottom of the destination vessel and rack on top of it. The siphon hose will circulate the mead and thoroughly mix it with the potassium metabisulfite.
AKA: PS, K-Sorb, K-Sorbate
Potassium Sorbate can be added to a mead to prevent any surviving yeast cells from reproducing. This helps to prevent significant renewed fermentation if there are very few living yeast cells remaining in a finished mead. Like potassium metabisulfite, its effectiveness and therefore the dosage required is relative to the finished mead to which it's being added.
When added to water, potassium sorbate works by breaking down into two substances: sorbic acid and potassium. Sorbic acid, 75% of potassium sorbate by weight, acts as an anti-microbial.
It does not inhibit all microbes, so it is important to be sure that your mead is stable, and to add potassium sorbate only in conjunction with potassium metabisulfite. In fact, Lactobacillus metabolizes sorbic acid to produce a compound that smells strongly of geranium leaves.
Sorbic acid has another drawback: in the presence of alcohol it will eventually form ethyl sorbate, which has an aroma reported to be similar to pineapple or celery. This could put an inherent shelf life on your mead; but, at very low concentrations, it may not be noticeable. It also isn't necessarily a flaw. Fruity characteristics can enhance some meads.
According to the University of Minnesota's Enology Blog post on the subject, there is "no clear consensus" on the required dosage, and the most frequently cited study comes from French enologist Émile Peynaud, in 1984.
> [Peynaud] notes that sorbic acid is half as effective at a pH of 3.5 than it is at a pH of 3.1, but then lists his recommended dosages based on alcohol content. Sorbic acid’s action against yeast is reinforced by alcohol.
> These recommendations by Peynaud assume a pH < 3.5, and adequate SO2 protection.
| Mead ABV | Sorbic Acid mg/l | K-Sorbate mg/l | K-Sorbate g/gal | K-Sorbate g/5 gal |
|---|---|---|---|---|
| 10% | 150 | 200 | 0.758 | 3.79 |
| 11% | 125 | 165 | 0.625 | 3.125 |
| 12% | 100 | 135 | 0.512 | 2.56 |
| 13% | 75 | 100 | 0.379 | 1.875 |
| 14% | 50 | 65 | 0.245 | 1.225 |
| †15% | 25 | 50 | 0.132 | 0.662 |
†The 15% row has been extrapolated for this wiki.
This linear chart suggests that the usefulness of potassium sorbate at higher alcohol content is reduced at higher ABVs, and is consistent with the ABVs that delle stabilization becomes practical.
As a meadmaker, you may decide that high alcohol content, aging, filtration, pasteurization and/or other factors render the addition of potassium sorbate unnecessary. There are some drawbacks to potassium sorbate as lactic acid bacteria can digest sorbic acid over years and make for a mild fault called geranium taint, and more naturally focused mead makers to not care for inorganic additives. It is however an extremely useful tool for the new meadmaker, meadmakers without access to other tools or methods, and for mead styles that don't lend themselves to other methods of sure stabilization.
Weight to volume testing conducted by /u/balathustrius suggest that potassium sorbate averages 1.95 grams per flat teaspoon.
When physically adding potassium sorbate to mead, be aware that it does not easily dissolve. It's easiest to dissolve it in a small sample before adding it back to the mead as described for potassium metabisulfite, above. It will not easily dissolve when added to the bottom of an empty carboy and mead is racked on top of it. The circulation is not necessarily vigorous enough.
With careful selection of yeast strain, careful dosage of nutrient additives you can cause a mead to ferment up to the yeast's natural alcohol tolerance and halt with some residual sugars, or add small additions until the yeast is no longer able to continue to ferment and ends sweet. This can be several points higher or lower than the value stated by the manufacturer, but is repeatable if you keep your process, specifically yeast strain, sugar load, pH and target final gravity, the same. This method assumes that you are trying to produce a medium-sweet to sweet mead, and is not reliable in dry meads until very high ABVs.
You may have trouble hitting exactly 14% with 71B-1122; but, if 13-16% is fine with you, this is a very easy calculation-light method of preventing renewed fermentation after sweetening and bottling.
Begin with a high enough starting specific gravity (and therefore potential alcohol) to reach the stated alcohol tolerance of your yeast. As long as it has enough nitrogen from nutrient sources, it should have no trouble reaching the published number. If it falls a point or two short, that isn't a big deal since you've accomplished the goal of stopping fermentation.
Monitor specific gravity as fermentation is tapering off. As it falls below 1.010, add enough honey to raise it back to 1.015 - 1.020. If you care about your final ABV, keep track of how much you had to increase the gravity and add that to your original gravity for the purpose of calculating ABV in the end. Eventually, fermentation will stop and the gravity readings will stabilize somewhere in the 1.010-1.020 range. This is similar to step feeding and will often cause the yeast to greatly exceed it's stated tolerance. If you desire an even sweeter mead, simply add honey to the desired sweetness level and continue to monitor the gravity. Diluting the alcohol content at this stage with additional honey may cause fermentation to briefly restart.
The other option is to put in enough sugar that the mead will end semisweet and then back
sweeten to taste from there. This generally only works at above 14% ABV, or with very high final gravity. The unit of calculation for microbial stability is called a Delle and is referenced by Mike Simmons here.
The formula is 4.5 * the %ABV + the % Residual Sugar. % residual sugar, known as RS, is the grams per liter of remaining sugar, divided by 10
For a 14% mead according to Simmons you need at least 1.006 FG in a stable reading to prevent restarts. Other sources, port and wine focused, list the Delle value for microbial stability as 73, which for 14% corresponds with a FG of 1.037. At 15%, the FG would be 1.020 for stability with a required Delle of 73. Both pH and temperature can effect Delle units, and Delle calculations are only valid if the fermentation has actually paused, either artificially through a cold crash, Campden addition or by a natural yeast halt due to ABV.
It is optional to still use chemical stabilizers when relying on alcohol tolerance. This largely eliminates the chance of restarts, and any stabilization should be carefully watched for continued fermentation.
If you use ABV to halt a mead and do not dose with stabilizers or another method, it is never certain that fermentation will not restart. It's possible that some yeast metabolic activity will happen during a lengthy storage especially with temperature fluctuation, making it possible to create bottle bombs. You can take the following precautions:
Allow the mead to age (12+ months) before bottling.
Drink it young.
Store the mead in a cool place with a stable temperature.
If you notice bottle carbonation, store remaining bottles in the refrigerator and drink up.
This is both the simplest and most complicated solution. It's simple in concept: sterile filtration is the removal of microbes by merely filtering them out of the mead! It's complicated because you need more relatively expensive equipment: pumps, filter housing, filter cartridges. Lastly, it's probably the most reliable method. It's widely used by the commercial wine industry, but is still within the price range of serious home meadmakers willing to spend a few hundred dollars on it.
Sterile filtration is done by pumping the mead from one vessel through a filter into another freshly sanitized vessel. You need a filter with pores .5 microns or below to achieve sterile filtration.
The process for filtration is going to differ depending on the pumps and filters you use. As an example of what it entails, this video is a demonstration of the Buon Vino Mini Jet Filter. I reiterate that there are a lot of options and that we're just using this as an example.
Pasteurization is a common stabilization method generally used to result in sweet, carbonated product. It can also be used when other methods are not accessible or desired for still mead. Pasteurizing inherently has some risks. You can have either incomplete pasteurization, you can boil the mead and over pressurize bottles, or heating can result in over pressurized bottles. Boiling can occur as low as 180F at high ABVs, and as high as 190F at low ABV. Heating from 60F to 145F increases bottle pressure by 16%. Important things to keep in mind while pasteurizing this way is that it is very important that any sugar distribution and pressure in the bottles is very uniform, and that bottles should be secured with crown caps or other closures that can hold pressure. Do not pasteurize bottles that had priming sugar or similar added separately to each. Typically when aiming for carbonation, a control bottle in plastic is used. When they are carbonated and firm you are ready to pasteurize, and the plastic bottle can be used as your probed bottle for your mead temperature.
For this method, always wear safety equipment and use bottles that don't show any signs of damage. Even small chips or cracks can lead to bottle bombs.
Monitor the bottles for carbonation progress by opening one every few days or wait for a plastic bottle to become firm. You must perform this process as soon as the desired level of carbonation is met. The desired pressure is firm to tight when pressure is applied, you then know that your glass bottles are carbonated. You can give yourself a test pour from the plastic bottle just to be sure.
Pre-heat the closed bottles in a sink or cooler full of hot tap water, somewhere around 100-120F. Leave them there while you complete the next step. This lessens the thermal shock and makes breakage less likely.
On the stove, bring a large pot of water up to 160° F. There should be enough water in the pot to submerge the bottle up to the neck. This step can be greatly simplified by using a sous vide controller/heater and a lower temp can be used, 145F. The safety and control of sous vide removes a lot of challenges of pasteurization.
Safety glasses, long sleeves and pants are a good idea. More protective clothing like gloves can be a good idea. Be mindful of your work area, popping bottles is a real concern. Remove the pot from heat if using a stove top. Bear in mind that temperature will continue to increase from stored heat in the pot. Monitor the temperature of a control bottle. 160F is enough to instantly pasteurize. When the mead is held at an internal temperature of 145F for 20 minutes this is also enough to halt fermentation, and that temperature of a water bath can be used if you have good control over the water temperature.
Remove bottles and allow them to cool. Store in a safe place in case pasteurization failed. Check carbonation on a bottle in a few more days to ensure you don't have a crate of time bombs.
Winemaker's Academy: Using Potassium Metabisulfite to Make Wine
Winemaker's Academy: Adding Potassium Metabisulfite to Wine
Winemaker's Academy: Using Potassium Sorbate When Making Wine
University of Minnesota Enology Blog: Potassium Sorbate as a Wine Preservative.
Brew United: How to Pasteurize Your Bottles for Sweet Carbonated Cider