I’ll be honest, this blog post contains all the biochemistry that I care to discuss for a long, long time. However, I do feel it’s important to touch on this to help set the record straight and clear up some of the misconceptions. I find the volume of information out there about this topic quite cumbersome; there are many articles written by “experts” (aka sommeliers, wine educators, bloggers) that while surely well-intentioned, contain many errors. Sulphur chemistry in winemaking is an extraordinarily complex technical topic, and I wish more educated, technical winemakers would respond to the inaccuracies and misconceptions that exist in the ether.
Let’s start with Sulphur, generally. It is extraordinarily abundant in nature, and its commercial uses include matches, as an odorant in things like propane, it’s a component in insecticides and fungicides. Yes, it’s a chemical. No, it’s not evil. It depends on the form and concentration it exists in. Water, for example, is a naturally occurring chemical compound. It’s necessary for life, but too much of it can kill you. The same goes for Sulphur; it is essential for life. It’s a vital component for some amino acids and vitamins, necessary for the life cycles of microorganisms (such as yeast), and used in a host of ways in the medical, food, and industrial sectors.
Are people allergic to some forms of Sulphur? Absolutely. Sulfa allergy, for example, is something you want to discuss with your doctor, as Sulfa-drugs are extremely common and powerful pharmaceuticals.
An allergy to sulphites is debatable. Some people have a bronchial reactivity to things like KMBS (potassium metabisulfite), which is a strong antimicrobial and antioxidant commonly used in winemaking and other food industries. This reaction causes asthmatic symptoms in some people, and I’m one of them… and I’m a winemaker. As such, when I am working with KMBS in the cellar, I take care not to breathe the fumes; it doesn’t kill me and I’m pretty sure it doesn’t make me stronger… it sure hasn’t helped my bench press.
Once the addition has been made to the wine and the concentration has been diluted (usually less than 60ppm as Free SO2), I don’t have an issue. Now I have tried wines that were easily 100+ppm Free SO2, but that’s uncommon and emblematic of poor, sloppy winemaking. Most people can start smelling SO2 at 60ppm and above. There is a legal limit set by our glorious overlords at the Tax and Trade Bureau; formerly part of the Alcohol, Tobacco, and Firearms agency. This is usually expressed as TOTAL SO2. A brief note about that: Free SO2 is different than Total SO2, and Bound SO2 is determined by subtracting the level of Free SO2 from the Total SO2 value. Legal limits are a good thing in my opinion and vary depending on the regulating country. There is plenty of information out there if you would like to google that topic. In the US, the limit is 350mg/L (ppm) as Total SO2… that’s A LOT! In the past, it would be common, but we thankfully we know about science and stuff this day and age… hopefully. There are the equivalent of flat earthers in the “winemaking” community. OK, that was mean. But seriously, if a wine has 350ppm of total SO2, something went terribly wrong.
Sure, the effectiveness of SO2 is pH-dependent, but with what we know about the interaction of SO2 and Dissolved Oxygen, there really shouldn’t be any reason for such high levels. The tools available for oxygen and microbial management are plentiful these days. In years past, SO2 was one of the only tools a winemaker had to keep wine safe from microbial degradation and premature aging.
So why use SO2? As mentioned above, it is a powerful antioxidant and antimicrobial. There are mentions of it being used in winemaking dating back to the Fifteenth Century, the Romans used it, and it is recognized by our other magnanimous overlords, the FDA, as Generally Recognized As Safe (GRAS). We are exposed to it in varying levels in our daily life; dried vegetables (100-500ppm), wine (50-150ppm), salad bars (400-1000ppm), dried fruits (1000-2000ppm). So when people tell me they are allergic to the sulfites in wine, or that they get a headache from it… cue the facepalm. The honest truth of it is that people aren’t allergic to the sulfites in wine, they are allergic to bad winemaking.
When I talk with people, I often hear they have a reaction to red wines, but white wines are just fine. If it’s truly Sulphur they are allergic to, their statements are incongruous. White wines typically have higher levels of SO2 compared to red wines. Here’s the reason why they have a reaction to reds: Malolactic. Technically, this is a biological conversion, a decarboxylation process as opposed to a fermentation per sea. The improper use of terminology, such as referring to Malolactic as a Fermentation, is a topic for a future blog post, yay!
Back to Malolactic Conversion: this is commonly done by different species of Lactic Acid Bacteria. Yes, there is bacteria in wine. It’s not gross, I promise… well actually in the case of Pediococcus sp it can be gross, more on that in another blog. There are three general paths the wine industry uses to complete Malo: “natural/native,” individual inoculation, and then a spread inoculation.
Before I get into the options for conducting Malo, let's discuss why you might want to. In the past, Malo was the second step after alcoholic fermentation that would help render the wine more stable from a microbial standpoint. There’s lore from the old world that the wines would go through alcoholic fermentation in the fall, then they would put them into barrels to “sleep” through the winter. They would “wake back up” in the springtime when temperatures warmed; this was Malo. The amount of carbon dioxide produced is much less than that of primary. Specifically: for every 1 gram of malic acid, .33 grams of CO2 is produced. Compared to primary fermentation, it’s not much, but if you bottle a wine without completing Malo, you can end up with a slightly fizzy wine and at worst corks popping out.
Microbial stability is one thing, flavor is another. The conversion of malic acid to lactic acid causes the pH to increase, and the TA to decrease; it “softens” a wine. There’s a host of other things regarding color, tannins, aromas, and mouthfeel that Malo can affect.
All that may be well and good, but what does that have to do with headaches and Sulphur? Well, generally, white wines do not go through malo, while most red wines do. Depending on which bacterial strain conducts the Malo, they can produce biogenic amines. Ok, Luke, stop saying sciency words! No, I will not. Most all of us are familiar with biogenic amines; the most common ones that come from a wild Malo are Hystamine, Tyramine, Putriscene, and Cadaverine. What do you take when you have allergies? That’s right, an anti-histamine. Hystamine and Tyramine are known to trigger headaches. The other two, Putriscene and Cadaverine smell exactly like you would think they do; putrid and cadaver.
Now, let's revisit the three methods a winery might choose to conduct Malo.
“Natural/Native”
I love buzz words. Oftentimes, they trigger a reaction in people. Look at the back of a generic wine label; you’ll probably see “family,” “farming,” “generations,” “craft,” “we select the finest grapes,” “limited production,” and on and on. I’ll share my thoughts about the warm and fuzzy words on labels that don’t mean a thing and are basically rote for the wine industry on another blog post (geez I’ve got a lot of writing to do). This is the issue with “natural/native;” it has no definition. Sure, there are general parameters that some producers fall into, but nothing legal, as it were. But at a high level, natural wines means little to no Sulphur added, and letting whatever yeast and bacteria are on the grapes or in the cellar, do the work. Often, the innuendo is that somehow “natural” equals healthy. Here’s the truth: wines that go through Malo using indigenous, or “native,” bacteria, have a much higher risk of being chock full of biogenic amines. So, if you’re trying to solve the red wine headache problem, natty wines are the wrong tree to bark up. If you want a higher rate of VA (vinegar), more biogenic amines, off-flavors, mousy taint, etc; then natty wines are your huckleberry.
That’s not to say that natty wines can’t be great, I’ve had some, but in my experience, it’s a losing game of Russian Roulette.
Spread Inoculation:
This isn’t common terminology in the industry, but the practice is widespread at wineries looking to pinch pennies. This is not relying on native bacteria populations. Most commercially available ML bacterial cultures are selected and known to not produce biogenic amines, they don’t have the metabolic pathway.
For spread inoculum, let’s assume you have 5 Cabernet lots. The first one to finish primary is inoculated with a known, selected bacterial strain. Once implantation has taken place, ie Malo is progressing nicely, a portion of that batch is spread out to the other Cabernet lots, thus inoculating the other lots (hopefully) with a viable population of the desired bacterial strain.
This method can work well, especially considering the cost factors. However, it’s indiscriminately sharing the microbial populations between the tanks and comes with an elevated risk of a stuck Malo.
Individual Inoculation:
This is the safest way to conduct Malo. Malo can be difficult to finish, depending on a host of factors. Selecting the right strain for the conditions it will be facing is the best way to ensure Malo finishes without issue. Since most of the strains available on the market do not produce biogenic amines, this means cleaner, better tasting wines that don’t cause headaches. One of the major reasons many winemakers don’t choose to inoculate each tank with its own Malo culture: it’s expensive. Statistically, this is the best choice to produce higher quality wines, but it comes at a financial cost.
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Hopefully, this has been informative, and cleared up some of the misconceptions and shed light on what’s really going on with sulphites, headaches, and flawed wine. It brings up an interesting phenomenon in the wine industry; how some winemakers will choose a certain path due to philosophy (aka natural winemaking) rather than proven science. It takes years to raise a crop of grapes, and many months to turn it into wine. Risking all that hard work and expense to play roulette with wine quality is a curious decision. On that note, I should point out that almost every strain of bacteria and yeast available on the commercial market was taken from nature, rigorously studied to identify its unique characteristics; long before it reaches the winemaking store shelves. In some ways, using commercial strains is just as natural as anything. If a natty winemaker wanted to be truly natural; they wouldn’t prune, train, thin, trellis, or use rootstocks in their vineyard. Truth is, grapevines have evolutionary programming to want to produce the ripest, most delectable grapes.
I don’t wish to admonish a natty winemaker, I appreciate their perspective and what they are trying to do. However, my goal is producing the best quality wine possible. I owe it to the grape grower to first, do no harm. I owe it to the consumer to bottle the best wine possible so that they get the best value for their hard-earned money. For these reasons, I use the individual inoculated method. Each batch gets its own implantation of carefully selected bacteria to conduct Malo. By doing so, I have the best chance to make the most flavorful, tasty, defect-free… and non-headache inducing wine possible.
Luke Holcombe
Partner, Director of Winemaking