Acid Metabolism During Fermentation

[ScotRob]

My question is fairly simple (but I will also post my recipe and results to date so you get the background, below): to what extent are various acids in acid blend (tartaric, citric and malic) metabolized and thus lost during fermentation?

I am following a recipe from a 70s book, the Penguin Book of Homebrewing and Winemaking:

For 1 gallon light mead:

2.5 pounds honey
4 level tsp acid blend
2 tsp vitaminized nutrient
0.25 tsp tannin
yeast (i used Gervin universal wine yeast)

My adaptation was to add more honey (approx 3.3 pounds) and the starting SG was about 1.105. Fermentation went rapidly and it fermented to dryness (SG 0.998) in around 2-3 weeks, but I am concerned about the acid level....4 tsp seems pretty high and in fact my tsp measurements were slightly mounded rather than level, although obviously the yeast didnt mind since it fermented so well. I racked off the lees into secondary at 3 weeks, topped up with honeyed water and am leaving it. Taste wise it tasted "hot" (as brand new meads often do), and very tangy (a bit too much in fact)....can I expect lessening of the acid as it ages/ferments out? I dont want to waste time on this if it will
never improve. Maybe just adding more honey each time I rack will be sufficient?

thanks

 

[Chevette Girl]

Hey ScotRob. Welcome to the forum!

Well, my first reaction to your recipe is "Holy crap, that's a lot of acid to add up front!" I'm glad your fermentation went well.

If you do a little reading around here, you'll find that honey has its own acid (do an advanced search for "gluconolactone" with the author Dan McFeeley for more info) and generally does not require MORE acid or else you run the risk of having too low of a pH for the yeast to work comfortably. Yours apparently got the job done anyway

You might want to take a look around here for some traditional mead recipes before starting your next one, generally we only recommend adding acids to a finished mead, and only if it needs it for taste.

Yeast also produce acidity, so even if the yeast metabolize some of the malic acid into the less acidic lactic acid (which maybe one or two yeasts are capable of but I can't recall offhand which ones, usually you need to add a bacterial culture after fermentation), you're still going to end up with more acidity at the end of a fermentation than at the beginning.

Now, for your particular situation with a finished mead: sometimes you can get spontaneous malolactic acid reactions during aging, I had one batch do that once, but short of adding chemicals or bacterial cultures, I think you're pretty much stuck with your current acidy level. Hopefully if one of the more experienced folks around here knows better, they will correct me.

Have you any idea of the pH of your mead?

If you want to decrease the acidic taste a little, I would recommend trying very small amounts of potassium or calcium carbonate to neutralize some of the acidity, like, less than 1/4 tsp per gallon, and give it a few days to reach equilibrium before tasting and determining if you need to add more. Too much calcium carbonate can leave a wine tasting chalky but so far I've used it sparingly without any problems.

It's possible that some combination of age and backsweetening may also balance the acidity a little. I don't know if addition of more tannin (or oaking) might help balance the acidity or if it would accentuate it.

 

[ScotRob]

thanks Chevette Girl! the pH is currently around 3.2, which doesn't seem to bad....although this is possibly too low to allow any MLF to occur

 

[Chevette Girl]

Keep in mind, vinegar is around pH 3... and mlf will only occur if you either happen to have the bugs kicking around in your must anyway, or add them, and they'll only deal with the malic acid as far as I understand the process. Mine was just blind luck at having some native bugs and the right conditions for it to happen spontaneously.

 

[ScotRob]

ok- thanks for the tip regarding MLF. I think what I will most likely do here is simply wait (I am loathe to simply throw the batch away) and keep rakcing and topping up (which will take out some of the acid too), backsweeten a bit, and see what it's like when it comes time to bottle....if it is still too tart then I will try the calcium carbonate method in tiny doses to see what happens....I actually prefer my wines quite crisp and tangy so I'm not too worried, although what I don't want is a sweet-and-sour mead.

Two other points to raise- 1. the honey I used for this was Linden (Basswood) blossom, which I am told has about the highest (least acid) pH of almost any honey...so maybe this will also help a bit?

2. I am currently drinking a nice crisp New Zealand Sav.Blanc wine which measures pH 3.3 (thus almost the same as my mead)....i know grape wine is different from honey wine, but I am taking encouragement from this since this wine is one of my favourites and just the right mix of dry and tangy

 

[Medsen Fey]

During fermentation, tartaric acid will not be metabolized. Some of it may precipitate out if the solution is saturated (unlikely unless you have a lot, such as in a pyment) and you cold stabilize.

Malic may be metabolized partially by some yeast. 71B is an example of one reputed to be able to reduce malic acid by around 30%. MLF with bacteria can reduce it further.

Citric acid is hard to predict. It can be metabolized by yeast during phases of their growth and development, but ofter they will secrete some, raising the level of citric acid. It varies by yeast strain.