There has been an increase in the interest in meadmaking among homebrewers in the past decade. This is due in large part to Ken Schramm’s book, “The Compleat Meadmaker” (2003, Brewers Publications), which introduced the “dump and stir” method of making mead without heating the must (the unfermented honey mixture). Not too long after the publication of his book, meadmakers discovered that you could get a more ordered fermentation if you staggered the yeast nutrient additions. This allows the meadmaker to dole out the nutrients as the yeast need them rather than adding all the nutrients at the beginning of the fermentation, and this leads to faster, more ordered fermentations.
Recently, I spoke to Schramm about two other things that have come to light in recent years that are required for optimal mead fermentations — the need to give the yeast sufficient potassium during fermentation, and the need to control the pH of a mead fermentation. By happy coincidence, you can do both of those by adding potassium carbonate (K2CO3).
In a traditional honey mead — a mead with no fruit or ingredients other than honey — potassium levels can vary wildly. Levels of 30–2,500 ppm potassium ions (K+) have been reported in various types of honey, with lighter colored honeys generally having lower levels (around 200 ppm). Once diluted with water, this range would drop significantly, depending on much water is added (at a minimum, around a three-fold dilution). However, in order to support a healthy fermentation, a mead must should have at least 300 ppm potassium.
In a traditional honey mead, as in beer or wine, the pH drops during fermentation. The pH of the initial honey and water mixture may fall into a wide range (3.5–5.0), depending on the acids in the honey and the level of carbonates in your water. However, the honey and water mixture is poorly buffered, and its fermentation can quickly drop the pH to a level below which the yeast are inhibited. (Below a pH of 3.2, most wine yeasts start to struggle.) A starting pH of 3.6–3.9 will allow the mead to ferment and reach a final pH of 3.0–3.2, and occasionally as low as 2.9. If the mead starts at 3.5 or below, it may ferment sluggishly or not at all. If you adjust the pH initially, you should not need to adjust it again during fermentation. (Note that some meadmakers start as low as 3.4, then adjust the pH if it gets too low during the fermentation.)
Although you could supplement the must with potassium by adding any potassium salt and separately adjust the pH with calcium carbonate or sodium bicarbonate, you can “kill two birds with one stone,” as Schramm puts it, by adding potassium carbonate (K2CO3).
How much potassium carbonate to add should depend on your initial potassium levels. Unfortunately, there is no simple way to measure potassium levels in your mead must at home. However, because parts per million is roughly equal to milligrams per L, you can easily calculate how much K2CO3 you would need to add to 5 gallons (19 L) to reach 300 ppm if your mead must had 0 ppm initially — 19.0 L * 300 mg/L * 138 (FW K2CO3) /39.0 (FW 2 K) = 10,100 mg or 10.1 g (or 0.36 oz). You could also use 14.6 g (0.51 oz.) of potassium bicarbonate (KHCO3 : IUPAC name potassium hydrogen carbonate) to 5 gallons (19 L) of must to yield the same thing.
If you have a pH meter, you should measure the pH of your must initially. If it is below 3.6, add a small amount (around a gram or two) of K2CO3, stir and keep adding small amounts until the pH climbs to this level.
So how much K2CO3 should you add, given that your potassium levels are unknown and the pH of your must may be over 3.6 naturally? Your first move should be to adjust your pH, if needed. If, in doing this, you add 300 ppm K+ or more to the must, then that’s all you need. If not, keep adding potassium carbonate until you have added a total of 10 grams (0.36 oz.) of K2CO3 to your must. This will result in 300 ppm of potassium ions added to whatever unknown (but likely small) amount of potassium in the must.
Ken Schramm is set to open Schramm’s Mead in a matter of weeks. His meadery will initially offer some melomels, and later some traditional meads (as they take longer to ferment). Most of his meads will be made with local Michigan honey and he is looking into becoming a beekeeper.