Composition of Grape vs Honey Musts, Part 2

This part will deal with yeast assimilable nitrogen. Now, we are all familiar with the concept that mead musts don't have enough yeast assimilable nitrogen (YAN), or at least they tend not to have enough for us to be comfortable with. Here, we will take a look, not only at the total levels of YAN, but which constituent parts are involved in the differences between grape and honey must.

What is going to be our baseline? That is a very interesting question as the specific amino acid profile of a grape must depends on the variety, specific clone, climate, vintage, soil type, and what vineyard practices occur. There are some basic profiles that can be drawn based on grape varietal, and differenced between red and white, so we will look at a few white varieties and the average for them. The same problem exists with honey: the specific amino acids and their ratios are heavily determined by floral source, but the weather will also play a major role (with drier weather usually meaning more pollen content, and thus more amino acids), as will the region (again having to do with nectar sources).

Just look how different they all are. To better illustrate the point, lets look at the profiles of an average white grape must, honey, and pollen.

Notice how honey and pollen have much higher levels of proline compared to the other amino acids, over half, while grape musts have proline representing about one fourth of the amino acids. Keep in mind that yeast can only use minute traces of proline (only when respiration is dominant compared to fermentation, which is incredibly rare in fermenting musts), and while arginine is utilized by yeast, they far prefer glutamic acid and glutamine, which show higher ratios in pollen (and therefore honey), in comparison to grape musts. 

Here we get to see how two different honey musts compare to average white grape must. The honey must with pollen (30g/L) is closer to the levels of wine must, but it still has a ways to go. This represents a mead must made with 3lbs honey per gallon, but changing the concentration of honey to water changes the amino acid levels to a considerable degree. 

The more honey, the more amino acids, but also a higher starting gravity. Increasing pollen additions also help add amino acids, and if your honey is not filtered you may have anywhere from 1g/L to 5g/L, though this still represents only a small increase in YAN (<20ppm), far from what is considered acceptable.

While pollen additions seem very effective, there can be a bitter flavor that accompanies the pollen, especially if it is of low quality (be warned, the majority of freeze dried pollen sold in the US is from china, even if the guy at the farmers market is selling it).

P.S. See . . . I told you more pictures! Also I'll get a half-a$$ bibliography soon; just a busy drone, even if I am male.

Composition of Grape vs Honey Musts, Part 1

This will be a series of articles that compare the constituent compositions of grape musts and honey musts, which is worse than comparing apples and oranges. Although we try to use similar practices on both for the production of wines and meads, there are intrinsic differences that can cause problems; but that also make each unique, even down to the specific grape variety or nectar source. These will not be all encompassing, comparing Russian River Pinot to Burgundy, or Arizona orange blossom to Floridian, but will serve as a guide to how we should treat our musts: what to add, when to add it, and what not to add it.

First we are going to take a look at the minerals in wine and mead. Why? Brewers worry night and day about their water, and for good reason; winemakers almost never consider it because whatever is in the grapes is considered good enough (most of the time); but mead makers don't tend to consider it at all, even though we are adding considerable amounts of it to our honey. As it stand now, no one has done a comparison of different water salt additions to test the organoleptic quality imparted by them, something I hope to do when I bottle some of last years traditionals. Until such time, all we can do is compare the minerals in mead musts to those of wine musts and try to guess what is going on and what needs to be corrected.

So, what specific minerals are we interested in? There are actually two questions there:

1. What minerals do yeast need for healthy growth? 
2. What minerals have an impact on the flavor of the product?

The first is readily available thanks to decades of extensive research on yeast metabolism and preferred growth media. The second is very hard in this context: I have yet to find any published papers on the effect of specific minerals on the quality of wine, let alone mead. Aside from obscure remarks about vineyard salt levels and the quality of grapes from them, it seems that no one is putting in any research on the organoleptic side. This is an area where brewers run circles around winemakers, and it is rather strange considering all the hype over the "minerality"of certain wines, although anyone who says they can taste slate is an idiot (go ahead, lick a piece of slate, then granite, and then quartz, they all taste the same; do it blindfolded if you want!).

To the right is a chart comparing the levels of common ions in wine musts, honey, and mead musts, as well as a common synthetic must that is used in experiments. From it, we can see just how different wine must, mead must, and what scientists think wine must is, all are. Wine musts have far greater levels of potassium (K⁺), magnesium (Mg²⁺), zinc (Zn²⁺), sulfate (SO₄^2-), phosphate (PO₄^3-), in fact, all the minerals listed are in higher concentration in wine musts than mead musts. This is just further proof that honey is a very inhospitable environment for most organisms.

So, the question remains: do we need to adjust these levels, or is grape must just in excess? For that, we need to look at several very important ions, and a few ratios, and ask they yeast what they want, what they need, and what they prefer.

Potassium (K⁺)
In brewing, potassium is not considered in a water profile because malt provides the amounts needed for yeast, but in wine and mead it is a very important consideration. Potassium plays a few vital roles concerning the yeast cell; first and foremost, yeast will uptake potassium ions in exchange for hydrogen ions in order to balance the pH in the cytoplasm. H⁺ is produced in several steps of glycolysis, and if allowed to remain in the cell, the pH will drop to fast and cause many problems with the glycolytic pathway (and several other pathways). The second role potassium plays is to increase glucose uptake rates via an unknown process that probably occurs with the yeast's hexose transport pathways.

How much potassium is needed? It depends on the amount of H⁺ ions within the medium. It has been shown that yeast need a molar ratio of 25-30:1 K:H in order to successfully complete a fermentation. If the ratio falls below this level, the fermentation is prone to sticking early, leaving a considerable amount of residual sugar. The amount of potassium needed can easily be calculated utilizing the pH of the must as seen to the right, but this calculation can be complicated when concerning mead due to the low pH buffering of meads. I'd suggest estimating how much you need based on the pH when the must is first created (before any additions are made), and just use that. To simplify matters, an addition of 0.25g/L (~1g/gal) potassium carbonate will yield 141ppm K, adding this value to the average 237ppm K in a SG 1.108 honey must gives 378ppm K, enough for a pH above 3.45. 1g/L cream of tartar  yields 208ppm K, and 0.25g/L potassium carbonate and 1g/L creamo of tartar added together will give 349ppm K, enough to supplement even the lowest K levels found in honey.

It is also important to note that supplying K later in the fermentation does not correct an initial deficit, so there is no point in waiting to add potassium.

Calcium (Ca²⁺)
Considered important by brewers because it stimulates yeast flocculation (and helps control mash pH), calcium is not terribly important in wine or mead making as the bulk aging time will easily clear yeast from the product. In fact, calcium acts antagonistically to magnesium and zinc uptake, and while small amounts (~1ppm) are needed for cell wall maintenance, it's use should be limited to low levels if any is added at all (be aware that almost all nutrient blends contain calcium as a cation attached to certain vitamins, and they usually contain magnesium to help balance this out). Also note that bentonite additions will add calcium to the product if used as a fining agent.

Magnesium (Mg²⁺)
As seen in the glycolytic pathway, yeast need magnesium for almost all cellular function, especially glycolysis. This is another mineral that brewers don't have to worry about because malt provides a ton of it; and winemakers tend to have enough of it, they just need to worry about if they have a proper amount compared to their calcium content. What is the proper amount? Something higher than 1:1 Mg:Ca. Many studies have been done showing that yeast function better with higher Mg:Ca ratios (2-4:1), but this may be excessive. I think a 1.5-2:1 ratio is right about where we should be to optimize yeast performance and not risk too rapid growth, zinc interference, or off flavors.

Sodium (Na⁺)
Have you ever noticed that Australian wines tend to be really savory, almost salty? This mineral is responsible for a lot of that flavor. Yeast don't need it, but it is always amazing how it can bring that cup of broth up to the next level, if used carefully. Brewers concern themselves with the chloride ion to give round, mouth-filling, savoriness to a beer, and some add a lot of salt (NaCl); others would never touch it and just use calcium chloride; but there is a difference between adjusting chloride levels, and adding sodium, and in moderation sodium just gives things that extra bit of something. How very scientific of me!

Chloride (Cl^-)
Chloride, just like sodium, has no important function in yeast metabolism, and is an unknown as far as flavor contributions to mead. The levels found in grape musts are obviously higher than those in mead, but most commercial nutrient blend provide small amounts in the form of thiamine hydrochloride and other vitamin or amino acid based salts.

Sulfate (SO₄^2-)
Sulfates are very important for yeast health as yeast need two sulfur containing amino acids (cysteine and methionine) which are often synthesized from other amino acid skeletons and sulfate via the sulfate reduction pathway. It is very important to note that this pathway relies on sulfate (SO₄^2-) and not sulfite (SO₃^2-) or elemental sulfur (S), of which the latter can lead to increased hydrogen sulfide (H₂S) production.

Sulfate is generally added as an anion attached to another mineral that we choose to add (ie. MgSO₄, magnesium sulfate). The addition of sulfate may have an affect on the flavor profile of wine and mead, though it is unclear what the impact is.

Phosphate (PO₄^3-)
Phosphates are very important for yeast metabolism (see how many times they occur just in glycolysis), allowing the construction of nucleic acids, energy transferring compounds (ATP), cell membranes and other internal structures, and are vital for the transport of extracellular compounds into the cell. Simply put, yeast needs phosphate, and honey does not have enough! The levels found in wine are on average 20-30 times those found in mead musts. Luckily, the P in DAP (diammonium phosphate) is there to help out; this compound is put in all non organic nutrient blends to provide both easy nitrogen, in the form of ammonium, and phosphates. A simple 0.25g/L addition of DAP will give 180ppm phosphate which is more than enough for yeast health. Note, however, that the 53ppm yeast assimilable nitrogen (YAN) provided by this same addition is normally not enough for mead musts; in order to get 212ppm YAN form just DAP, an addition of 1g/L is needed, which results in 719ppm phosphate (almost double the levels found in the highest testing wine samples, and above the legal limit of some countries).

Trace Minerals
Small amounts of manganese (Mn), copper (Cu), iron (Fe), molybdenum (Mo), boron (B), zinc (Zn), cadmium (Cd) and even lead (Pb) are present in grape musts with the table to the left representing an "average" Portuguese white wine must. Manganese tends to run at about 0.5-7.3ppm (mean of 2.7ppm) in most european wines, and zinc is be all over the board from 0.1-10ppm (with some chinese musts registering >12ppm). Typically lead is below 1ppm, as well as copper and iron. Almost all the same trace minerals can be found in honey, but in much lower quantities, with almost no copper or iron.

Fermentation rates seem to be best when there is about 2ppm Zn, 11ppm Mn, and 15ppm Fe, however those concentrations of manganese and iron would clearly impact flavor, and as they are not essential (above trace amounts), there is no need to supplement musts with them. Zinc, however, can have a major impact on the progress of fermentation and should be supplemented to sufficient levels (servomyces works very well at the recommended rate of 8.5ppm (0.32g/gal)).


Takeaways

• Add potassium, even if you don't have a way to measure pH, your must is probably lacking
• If you can measure pH, use the chart to guess how much you need, keeping in mind that any addition will raise the pH
• We don't know what flavor is added or changed, by what ion, yet
• Don't worry about calcium, maybe try to get it to >50ppm if you want, but make sure you add enough magnesium
• Add enough magnesium to get to about 100ppm, or about 1.5 times the calcium; remember that nutrient blends usually have it so don't go too crazy, maybe 2g/gal epsom salt
• Sulfates are needed, but are usually provided by nutrient blends or added epsom salt
• Phosphates are covered by DAP additions
• Trace minerals are present, but zinc may need to be added 
• Lighter honeys have less minerals than dark honeys, but not by a lot

Birch, Rosslyn M., Maurizio Ciani, and Graeme M. Walker. "Magnesium, Calcium and Fermentative Metabolism in Wine Yeasts." Journal of Wine Research 14.1 (2003): 3-15. Taylor & Francis Online. 04 Aug. 2010. Web.

Kudo, Masayoshi, Paola Vagnoli, and Linda F. Bisson. "Imbalance of PH and Potassium Concentration as a Cause of Stuck Fermentations." American Journal of Enology and Viticulture 49.3 (1998): 295-301. Print.

Larcher, Robert, and Giorgio Nicolini. "Elements and Inorganic Anions in Winemaking: Analysis and Applications." Hyphenated Techniques in Grape and Wine Chemistry. Ed. Riccardo Flamini. Chichester, England: John Wiley, 2008. N. pag. Print.

Ribéreau-Gayon, P., Y. Glories, A. Maujean, and Denis Dubourdieu. Handbook of Enology the Chemistry of Wine: Stabilization and Treatments. Chichester: John Wiley, 2006. Print.

Ricardo-da Silva, George/Jane M., H. Mira, P. Leite, and A. S. Curvelo-Garcia. "Metal Reduction in Wine Using PVI-PVP Copolymer and Its Effects on Chemical and Sensory Characters." Vitis -Geilweilerhof 46.3 (2007): 138-47. Print.

Somda, Marius K., Aly Savadogo, Nicolas Barro, Philippe Thomart, and Alfred S. Traore. "Effect of Minerals Salts in Fermentation Process Using Mango Residues as Carbon Source for Bioethanol Production." Asian Journal of Industrial Engineering 3.1 (2011): 29-38. Science Alert. 29 July 2011. Web.

Stobbaerts, R., H. Robberecht, F. Haesen, and H. Deelstra. "Manganese Content of European Wines." International Journal of Vitamin and Nutritional Research 64.3 (1994): 233-36. Print.

Sourcing honey

Honey is the most important ingredient in mead (duh!), and using quality honey is the first step to making quality mead. But how do we get it? Where can I find it? And what is it?

Let's start with what quality honey is. I'm going to say that unheated, minimally filtered, fresh honey is the best; we'll call this "raw" honey. Having said that, not all "raw" honey sold meets this definition: many products labelled as such have been heated and filtered beyond what I would prefer. It is very important to get to know your beekeepers for this reason, but I'll get to that in a bit. You should also be aware that not all honey that matches my definition tastes good, some types of honey, from certain vintages or floral sources, just tastes downright bad. Some honeys taste great, but make bad mead. And some honeys taste terrible and make great mead. Some need to be blended with other types and end up being very interesting, or they can ruin a batch. This is all part of the risk in using exotic honeys, or trying new honeys that you haven't had before; and there is very little advice anyone can give for many of these as they may work great sometimes and turn out bad other times, it's a matter of personal taste.


Where to find honey
 Start local; it will be fresh and you may know exactly where it came from. It also give you a sense of "terrior" in your mead making (sorry to use the controversial wine term, but it's the best way to get the idea across). I will also say that small does not always mean better; a large honey producer who cares about his product is better than the small "honey guy" who has no concept of quality.

Your first stop should be any of the several homebrew/meadmaking/winemaking forums. Post something saying where you are and try finding mead makers in your area. You can also try your local homebrew shop; ask if anyone makes mead in the area, they might also have local honey and a quick conversation with the owner may get you somewhere.
Next stop is the USDA honey board locator. While it will not list all the producers in your area, you are bound to find some. They usually list some form of contact information (website, email, phone, etc.) that you can use to contact the producer. The site also lets you see what the common honeys produced in your state are.


Local farmers market are your friends when it comes to finding local producers. Any good farmers market should have a honey booth (or several), and if it doesn't try another one. Try as many as you can drive to, and try them several times a year as some honey producers don't show up year round. When you do find a honey booth, try every sample they'll let you have, if you have to give the guy 5 bucks/quid/euro/whatever do it.


The next thing to try is a local Whole Foods, health food store, or other hippie store (no offense, again best word for the job). Go to their honey section (usually near maple syrup) and look for any products labelled as local, or start looking at the containers to find the producers address and try to find one that's near your area. Buy some honey from the producers you find and start tasting it; if it's good, try to contact the producer. If you don't have a hippie store in your area, move (seriously, it's probably a bad indication no matter what you views are). Local supermarkets (the publix/target type, not Walmart) sometimes carry local honey as well, try to find some and contact the producers.


After this, if you can't find anything local your in a tough spot. You can try contacting your local university extension office and see if they have any registry of apiarists, or a local club. Even a hobby beekeeper can produce a decent surplus that you can buy or trade some mead for. Don't be afraid to stop at roadside honey venders either, they usually have their own hives or buy from someone local.


Honestly, if you can't find a local beekeeper your either not looking hard enough, or your in a place that humans should not live. However, there are a number of alternatives.


Many large scale apiarists have websites and commonly ship honey cross-county. Beefolks has high quality honey at a good price and can ship you many different varieties. Dutch gold, while limited in offerings and processing their honey a little too much for my preference, is another such company.

The last resort should be generic store honey. Costco's, BJ's and Sams club all have large containers of honey. I find Costco's to be the best of the three, but all are cheaper than regular supermarket honey.


Befriend your beekeeper(s)
 While not necessary, it is a very good idea to get to know your beekeeper. He'll let you know what crops aren't good in a certain year, and can point you toward some interesting rare honeys he might get. After you've tasted his honey selection and deemed it worthy, bring a bottle of mead and offer it to him, if he refuses for reasons other than religious or philosophical, check to make sure he's not a Dalek, cyberman, or other "bad guy". Often times a reduction in price can come with buying a certain volume or bartering with mead, and a good level of trust in the person supplying your most precious ingredients is not something to shy away from.



Diversify
 The best strategy for any investment portfolio, and trust me, mead making is an investment, is to diversify your sources. I get most of my honey from two local sources, one in central Florida (Webbs honey) and one in south Florida (Smak attack, or something like that) by me. The first is a larger producer who can sell by the barrel, and I get great consistency from him. The latter is very small and gets certain rare honeys that are hard to come by. There is a price difference, but there's also a difference in hive locations which allows for more complex meads via blending (either within varietal boundaries or not). I have also bought from larger online producers, and roadside vendors, and even used generic bulk honey for some melomels (though I tend not to anymore). The more options you have, the more creative you can be, and the better bargain you can get. I think the strategy of "infinite diversity, in infinite combinations" is a very good one to adopt when it comes to honey varieties and mead making (is my geek showing?).

Mead: Etymology Part 1

I have a fascination with linguistics, particularly etymology. So instead of the standard "here is how to say mead in 20+ languages", I'd like to take you on a journey through the Indo-European language family via a single word: *med^hu.
First a quick note on some linguistic things. The * means that the word is reconstructed, meaning "we don't really know, but this is a very, very, very good guess that a few dozen people, with a few dozen letters following each of their names, have come up with using historical linguistic techniques (like comparative analysis, and internal reconstruction)". A proto language" is a hypothesized language that would account for similarities between several other languages; strictly speaking it is the youngest language that contains traits of several members of a language family or subfamily.
Proto-Indo-Eutopean (PIE) is the hypothetical language that led to all Indo-European languages; it was probably highly inflected, and would have had a considerable number of crossover words that could have meant the same (or similar) thing(s). Over time, PIE broke apart (probably into dialects which would later represent individual proto languages) and formed different branches of the Indo-European language family, which in turn broke into further classifications or became extinct.

This diagram represents the Centum languages in the Indo European language family; what one might consider the "european" groups. The gray/grey areas are proto-languages for which we have reconstructed words. The yellow/gold indicate languages for which the word listed means mead (or honeyed, sweet, alcoholic drink). Note that the Mycenaean language is in teal due to the fact that the liner B script used to write their language was borrowed (probably from the minoans) and does not fully account for the sounds of their language (ma-tu-wo could have been spoken as matuw, matwo, matuwo, or any number of variations). 

*méd^hu vs *mélid 

All three of these words could have been used to describe what one harvested from a beehive (honey).

*mélid  survived to specifically mean honey in many branches of the language family (greek, celtic languages,  italic languages, anatolian languages, and even germanic languages usually evolving into the word mildew (I have no f**king clue why!)). 

Mead/Wine/Drunk(eness/ard)

It is interesting to see that the etymological root word *méd^hu came to mean a number of things. In it's original form from PIE, it may have meant any drink made with, or having a honey-like flavor, but also could have specifically meant mead (I could describe sauternes as *méd^hu, but I would not call it that as it's name (adjective vs noun sort of idea)).

In hellenic languages it came to mean wine by the time of Old Ionic, and by modern it means drunkenness, and stands in ablaut relation to the word that means drunkard. It also stands as the root for the words that come to mean methanol, methylene, methyl, and methane.

Of very interesting note is the complete disappearance of this word from the italic languages, only for them to re-invent a word for it. I could list theories and cite shady evidence, but it does no good to do so. It is more interesting to see the word that the italic languages use for mead: 'water' + 'honey'. Note that I do not say 'water-honey' as a single idea, if that were the case Spanish, French, Portuguese and Catalan would all have similar phonology (sounds), instead of the obvious translation of 'water' + 'honey'. 

The Germanic and Celtic languages preserve this word and the meaning almost in its entirety. Mjothr, mid, mead, met, meede and medd all descend (rather obviously) form the same historical root, *méd^hu, and all preserve the meaning of fermented honey, regardless of how rare the term is, or how niche the word in their respective cultures (with the older ones probably retaining it's use more than the surviving ones).

Honey Composition: Acids

An acid can be described as any chemical that donates a proton (note this post will use the Brønsted-Lowry definition). They can be simple ionic compounds like HCl (hydrochloric acid), or complex molecules like CH₃COOH (acetic acid). They can be strong or weak (relative terms to describe how easily they disassociate, measured via pK_a ), organic or inorganic (containing carbon, or not), but all have an important role in mead making (and winemaking, even brewing).

Why are they important? Take a glass of cheap pinot gris and add lye (NaOH) to pH 7, taste it. It's terrible; lacking body, aroma, flavor, depth, everything. Acids are flavor enhancers, and they all have aroma or flavor contributions. They can also combine with other chemical to make new aromas and flavors (via esterification, acting as catalysts in reactions, or any other number of changes they themselves can undergo).

TA vs pH

TA stands for Titratable Acidity (not total acidity), and is a measure of how many free Hydrogen ions (H⁺) are available to react with a strong base (usually Lye (NaOH)) in and acid-base titration. Compare this to Total Acidity which is a measure of all H⁺  available in a solution from acids (even if they are not disassociated) using spectrometry or chromatography. Total acidity will always be greater than titratable acidity, but I don't have a gas chromatograph to take advantage of (and I doubt many home wine/mead makers do), so titratable acidity is the common language.

pH is a measure of the concentration of active H⁺, and it can only give you an estimate of the amount of acid in a solution. Because H⁺ can react with a number of compounds and get bound up, pH can not accurately account for the true amount of H⁺ ions.

Units

So how do we quantize this data? How can we put it into scale? Because we are looking to count the number of H⁺ ions in solution we can use a fancy trick: there are 6.02214129×10²³ things per mole. Atoms, molecules, muons, whatever. There are that many per mole. What's a mole? It's6.02214129×10²³ things! It's really just a useful conversion tool that allows us to convert from tiny masses, to numbers of things in a larger mass, and some other useful conversions. The atomic weight of H is 1.008, and 6.02214129×10²³  H atoms weigh 1.008 grams. See, useful conversions.

Now for something interesting. Tartaric acid has 2 H⁺ ions it can loose (making it diprotic), so a mole of tartaric acid should contain 2 moles of  H⁺. Citric acid is triprotic (3  H⁺), so a mole of citric acid contains 3 moles of  H⁺ (for those playing along thats 1.80664239 x 10²⁴ H⁺ ions). One mole of Lye (NaOH) has 1 mole of OH^-, and can react with 1 mole of H⁺ to make water (H⁺ + OH^- = H₂O). So 2 moles of NaOH can neutralize 1 mole of tartaric acid (because it's diprotic), and similar for other acids. So we can just count how many moles of  H⁺ it takes to get to a certain pH and get a measure of the amount of  H⁺ there is; this is titratable acidity.

The amount of  H⁺ in solution can be measure in equivalents, with 1 mole of H⁺ equaling 1 Eq of H⁺  (with the amounts we'll be using, the miliequivalent (mEq) is more practical, being 1/1000^th of an equivalent). Once in this measurement it is easy to convert to other acids (saying the amount of H⁺ in solution is the same as X amount of some acid in solution).

1 mEq/L H⁺  = 0.0750435 g/L as Tartaric Acid

1 mEq/L H⁺  = 0.0490395 g/L as Sulfuric Acid

1 mEq/L H⁺  = 0.06005 g/L as Acetic Acid

1 g/L = 0.1 g/100mL = 0.1 %

In the US it is common to write the acidity as a percent, but it is easily converted to g/L. The US, and most of northern Europe report acid as equivalent to tartaric, while Latin countries, and southern Europe report as sulfuric acid. Volatile acidity (a fault in wines and meads) is reported as acetic acid.

Organic Acids in Honey

Organic acids are those acids that are organic compounds (containing carbon). Honey contains, on average, 0.57% organic acids by weight. They can be categorized as aromatic (containing an aromatic ring like benzene) or aliphatic (non-aromatic). Many of the acids in this group are carboxylic acids (containing a carboxyl -COOH group).

Gluconic Acid HOCH₂(CHOH)₄COOH - The predominant acid in honey, responsible for much of it's unique flavor. Gluconic acid, and it's related salts, are added as a flavor enhancer in many foods. It is a product of the enzyme glucose oxidase reacting with glucose to produce gluconolactone, which in turn forms an equilibrium with gluconic acid (as a byproduct of this equilibrium reaction, hydrogen peroxide is formed, a powerful antibacterial). This reaction is pH dependent and any change in pH (via titration, or dilution) will shift the balance of the gluconolactone/gluconic acid equilibrium. 

Acetic Acid CH₃COOH - The acid responsible for vinegar, it's flavor and aroma are very distinct and detectable at a low threshold. It is generally considered a fault in wine (volatile acidity), but trace amounts will always be present as a metabolic byproduct of yeast.

Succinic Acid HOOC-(CH₂)₂-COOH - A non aromatic acid that is added as a flavor enhancer to many foods. Commonly found in all fermented products, it is a byproduct of yeast metabolizing nitrogenous compounds. It is very rare in unfermented grape musts; as such mead will have a comparatively higher level than many other fermented beverages. It also produces several esters responsible for general "fruity" aromas in wines.

Mailc Acid HO₂CCH₂CHOHCO₂H - Green apple. That's the flavor, and where it was first isolated from. It's what gives Riesling it's gripping acidity, and what Chardonnay fans want completely gone (via malolactic fermentation). There are trace amounts in honey that add to it's depth of flavor.

Lactic Acid CH₃CH(OH)COOH - This is what gives yogurt and sauerkraut their zing. Also responsible for the gripping acidity of a great lambic beer, or the gentle fullness of many red wines. 

Citric Acid  C₆H₈O₇ - The acid responsible for citrus fruits' sour notes. 

Butyric Acid CH₃CH₂CH₂-COOH - An aliphatic acid that has a slight rancid aroma, and is common in milk products (more in goat than cow).

Formic Acid HCOOH - This is what gives ant bites and bee stings their punch. It has a very unique flavor, slightly acetic, chemical, and spicy (?) note.

Amino Acids

An amino acid is simply an organic compound that has a carboxylic acid, and an amine group with a unique side-chain that determines the specific characteristics of the compound compared to others. Honey contains very small amounts of amino acids (0.05-0.1% by weight), with proline being the most commonly abundant (though some varietals have higher levels of glutamic acid or tyrosine).

Amino acids act as a source of assimilable nitrogen for yeast, and can be used in several steps of glycolysis, though the low levels in honey show that mead musts are a nutrient poor environment.

Argine, asparagine, glutamine, serine, aspartic acid, glutamic acid, threonine, glycine, alamine, proline, gamma-Aminobutyric acid, valine, phenylthalanine, isoleucine, leucine, ornithine, lysine,  tyrosine, methiomine,  tryptophan and histidine have all been found in honey, though methiomine, tryptophan, and histidine are very rare.

It has been shown that amino acid profiles are unique to individual monofloral honeys, and determination of the ratios between them can positively identify the primary nectar source of many monofloral honeys.

pH

pH is vital for yeast, as many reaction are catalyzed at low pH, and yeast use this to their advantage metabolically. It is also important to how we perceive the flavors of foods and drinks (we generally prefer acid tastes (low pH)).

pH = - Log [H⁺]

The above equation shows that pH is a logarithmic function of the concentration of active H⁺ ions, meaning that there are 10 times more H⁺ ions (that are not bound, and able to react) at pH 3 than at pH 4. Most people are familiar with the 0-14 scale with 7 being the theoretical pH of distilled water. Common wine musts ranges are 2.8-4.2, with finished wines ranging from 2.8-3.6 (whites lower (3.0-3.3 common), and reds higher (3.3-3.5)). WInes below 3.0 are rare (santorini can have as low as 2.8) because the yeast will struggle as the pH drops below 3.0; whereas above 3.6 oxidation reactions happen very fast, contributing to premature oxidation, and at 4.5-5.0 bacteria rapidly reproduce.

These values are useful only for an estimate. Mead does not act the same as wine. Why? Buffering. Buffering is a substance's ability to resist a change in pH. Wines have good buffering capability due to the high mineral composition (relative to honey) and their large amounts of weak organic acids (such as tartaric acid). Honey does not have high mineral content, or acid levels comparable to grape musts. As such, it is quite common for an all honey must to drop radically during fermentation (yeast will actually lower the pH of the substrate, and due to a lack of buffering it can fall too quick) , to such a point that the yeast struggle and can produce off flavors or not finish a fermentation. This is a big problem, but an easily fixed one: add buffering capacity! It is common to add carbonates for this purpose, and of all carbonates, potassium carbonate is preferable, not only because it is more soluble than calcium carbonate, but it also provides potassium which is a required yeast nutrient. The other additive that serves the buffering purpose is cream of tartar (potassium bitartrate). This is one of the natural buffering substances in wine, and it has been used for mead for some time (Morse recommends it, and latter in his life, Brother Adam also condoned it's use). I will note, that when using these additives your must may actually rise to pH>4 (which wine makers will advise against), but most of the time (almost all the time) it will drop to normal levels during fermentation.

Adjustments

Winemakers will often adjust pH and TA pre fermentation. This is a bad idea for mead as an acid added before fermentation will make the pH drop faster than normal, which is already a problem in mead. For this reason it is recommended to add acid only after fermentation. There are 3 main types of acid that can be added:

Tartaric - the main acid in grapes, it has a general smooth, acid flavor; it adds a generic fruit-like flavor to wines and meads

Malic - the main acid in apples, it is very sharp and angular; responsible for rieslings crisp nature, and adds a fruitiness to the flavor of a wine/mead often reminiscent of green apples

Citric - yep, it's what gives citrus fruits their zing, less sharp than malic, but more than tartaric; it can give a citrus-like impression to wines and meads and can be inappropriate for some styles

Additionally, there are many formulations of blends, some including all 3, other only two. The acid you choose depends on taste preference, style, and end goals. For example, if I made a light 10%abv mead with orange blossom honey, and was inspired by german riesling, I would probably add citric acid to highlight the citrus notes of the honey, and malic acid to give it the crispness of a good riesling. Generally, I prefer tartaric. The main reason is that it's the least obtrusive of the bunch, only adding a slight fruity flavor and not giving the impression of other, more specific fruits. It is also the fastest way to lower the pH, which can add an impression of acid. If tartaric is used, you should cold stabilize the mead to precipitate potassium bitartrate, that way the crystals do not appear when the mead is chilled in the future. This procedure has an added benefit: if the pH is below 3.6(5), then it will drop as the potassium bitartrate precipitates. This means that some of the acid flavor will be lost, but the pH will be lowered giving the impression of acid, making an acid addition even less obvious.

The real problem with TA

Simply put, TA cannot be measured accurately in mead. At least not by using the simple titration that many winemakers take for granted. In a normal titration the pH is adjusted to 8.2 with NaOH, but in homey this will not work like we want. Recall that the predominate acid in honey (and therefore mead) is gluconic acid, which exists in equilibrium with its lactone form gluconolactone. As the pH increases (via NaOH addition for titration) the actual amount of acid changes and the pH is lowered by this continuos equilibrium reaction. This characteristic of honey requires us to measure the free and lactone acidity separately, and add them together to get the TA.

I will be posting the exact procedure for this in the future, but it can be found in USDA Technical bulletin 1261 on p55.

Numbers vs Taste

So, we can't easily measure TA, but we can measure pH. OK, what number should my mead be? That would be too easy, and no fun. The best number to use is the one that works. You can pull some samples of the aging mead and start adding acid to them. Stop when you get to one that tastes great. Figure out how many g/L that is and add 10% less to the batch. Age and taste in a month. As for pH, as long as it's below 4.0 it's fine (though the lower, the slower it ages).

White, J.W., 1962, Composition of American Honeys, USDA Technical Bulletin 1261

Carratu, B., 2011, Journal of ApiProduct and ApiMedical Science, Vol. 3 No. 2, p81-88

Honey Composition: Sugars

Sugar; its the thing we care about in zymurgy because it what yeast metabolize to make (in the end) ethanol. Mead is differentiated from other fermented beverages due to the use of diluted honey; so it makes sense that we should care about the exact sugar composition of honey. We'll break things down into a few classes of sugars so that things can be gleamed from a larger perspective.

Monosaccharides 
These are the base units from which other sugars are made through different links. They can generally be classified by the number of carbon atoms in the molecule (pentoses have 5, hexoses have 6, heptoses have 7), and can be further classified by their functional group. Honey is about 69.5% (by weight) monosaccharides.

Glucose (D-Glucose, Dextrose) C₆H₁₂O₆ - The sugar. This is what the yeast actually prefer (being glucophilic), metabolizing it faster than other monosaccharides and faster than the production of enzymes to break down other sugars. On average honey is ~31% glucose, though it can vary from 22%-40% based on nectar source and age.

Fructose (D-Fructose, Levulose) C₆H₁₂O₆ - The other sugar, found in almost all fruits. It may have the same formula as glucose but the placement of the atoms are different (it's an isomer of glucose). Yeast will almost never completely consume fructose in the presence of glucose, leaving some residual fructose in most wines. Honey is on average 38%, with a range of 27%-44%.

Fructose/Glucose (F/G) ratio - Much is made about this number in analytical winemaking. In their under ripe form, grapes have higher levels of glucose, and as they ripen the fructose levels increase until picking (with an optimum ratio of 1:1 as seen by most winemakers). As seen by the numbers, the F/G ratio in honey favors the fructose side more than many wine grape varieties. This may result in more residual fructose in mead than in a comparable wine.

Disaccharides
Composed of two monosaccharides linked together, these require breaking by different enzymes produced by yeast in order to form monosaccharides that yeast can metabolize.

Sucrose (Saccharose) C₁₂H₂₂O₁₁ - Fructose and glucose held together by a glycosidic linkage. Yeast produce an enzyme called invertase which breaks this bond and allows the yeast to consume the derived monosaccharides. The average found in honey is ~1%, with a range of <1%-8%.

Maltose C₁₂H₂₂O₁₁ - Two glucose molecules joined together. Yeast excrete the enzyme maltase which breaks this molecule down to 2 glucose molecules. Honey has an average of 7% with some having as low as 3%, and others having up to 16%.

Turanose C₁₂H₂₂O₁₁ - Fructose and glucose bonded together. Trace amounts are found in honey

Maltulose C₁₂H₂₂O₁₁ - Fructose and glucose bonded with the same type of bond as maltose (and can be broken down with the same enzyme). It is produced via enzymatic reactions within honey between sucrose and enzymes present. Trace amounts are found in honey.

Kojibiose, Isomaltose, and Nigerose C₁₂H₂₂O₁₁ - These are made from 2 glucose molecules and are commonly found when glucose goes through caramelization and oxidation reaction. Trace amounts are present in honey.

Higher Sugars (Oligosaccharides)
These are the larger sugar compounds that contain more than 2 monosaccharides. The average amount in honey is ~1%, with a range of <1%-9%. Most of these are not fermentable (or partially fermentable in specific circumstances).

Melezitose C₁₈H₃₂O₁₆ - This is found in honeydew (a substance produced by certain insects commonly used by bees for food) and is present in all honey even if it is a nectar honey. It can undergo hydrolysis producing glucose and turanose. Trace amounts.

Erlose C₁₈H₃₂O₁₆ - Trace amounts.

Kestose C₁₈H₃₂O₁₆ - Glucose and 2 fructose molecules. Trace amounts.

Raffinose C₁₈H₃₂O₁₆ - Galactose, glucose, and fructose. Trace amounts.

Dextrantriose C₁₈H₃₂O₁₆ - Trace amounts.

OK. What does this mean? While the complexity for wines usually comes from an abundance of aromatic compounds, it seems that honey has a very complex sugar profile that is not found in many other products.

Variations
At the top of the post you'll notice a chart comparing many different varietal honeys. Ken Schramm's book The Compleat Meadmaker has a similar chart on pgs. 96-97, both his chart and mine are compiled from the same raw data (with some differences in which samples were chosen): Dr. White Jr's study Composition of American Honeys.  Why can such a chart exist? Because honey from different nectar sources shows marked differences in the sugar profile, and while this may vary with vintage and location, the difference is less than the difference between different nectar sources.


Age
The length and condition of storing honey has an impact on it's sugar profile. To the right you will see a data table showing how the composition of honey can change over time, however it does not agree with the findings of Dr White Jr.



Here are two graphs of the table above.

In Dr White's findings, he states that there is a decrease in both fructose and glucose as honey is stored. He also notes that the reducing sugars (maltose here) increase, as well the sucrose and higher sugars.


Looking at the graphs, none of these seem to be correct. The data from the above two graphs is from an experiment that used "a honey sample of 1kg . . . collected and mixed with 1kg of winter store after it had been deposited by bees from the syrup (sucrose:water ratio of 3:2) fed to them". What?! It has been common practice for quite some time to remove as much honey as possible from hives and to feed the bees a syrup that is supposed to provide the same benefit as honey. Using this method beekeepers can collect >90% of the honey in the hive, where traditional methods (leaving some honey behind for the bees) cannot come near this.

Why have I reported this data if it is useless? I'll quote from Dr White:
"These Changes [changes in sugar due to storage] are in the direction of increased complexity of sugars. They are probably brought about by two mechanisms – chemical and enzymatic. A high sugar concentration and a considerable acidity, both of which are present in honey, are known to promote a slow combination of simple sugars. It is also thought that the enzymes in honey bring about slow increases in the amounts of more complex sugars."

What this means is that honey increases in complexity as it is stored, while it would seem that techniques used by very large beekeepers deprives honey of this aging potential. This may become useful if you wish to highlight certain aspects of a honey, or are looking for more complexity in your mead; or if you forgot you had some honey, you can use it and know that it will be slightly different than fresh honey. If I were you, I'd get to know my beekeeper and make sure that it is truly quality honey, even if the price is more.


Rybak-Chmielewska, H., 2007, Changes in the Carbohydrate Composition of Honey undergoing During Storage, Journal of Apicultural Science, Vol. 51 No.1, p39

White, J.W., 1961, A Survey of American Honeys 3. Identity of Honey Sugars, Gleamings in Bee Culture

White, J.W., 1961, A Survey of American Honeys 8. Effect of Storage on Honey Sugars, Gleamings in Bee Culture

White, J.W., 1962, Composition of American Honeys, USDA Technical Bulletin 1261