Learning & Insights

Take a deeper-dive to learn more about the wine industry and insights into the winemaking process.

We use this page to periodically discuss the different facets of the winemaking process.  

Click or touch each topic to expand and learn more...

View our 2-part series of the 2023 Vintage: "The Crush" & "Fermentation"

Facts & Myths about Sulfites in Wine

By David Jammalo - July 22, 2023

The use of sulfites has been a contentious subject for some people.  However many facts are misunderstood.

What are sulfites and why are they in wine?  

What are the facts about the health effects? 

Do European wines have sulfites?


First, as a disclaimer, I am a winemaker and not a qualified physician.  This information does not constitute health advice.  I am qualified as an educated winemaker and not an expert in chemistry or health.  So take it as just a way of expanding knowledge about the industry.  But I give factual references so the information is scientifically verified.

What are sulfites and why are they in wine?

I’ll start with the first question.  Sulfites (or Sulphites) are actually various forms of sulfur dioxide (SO2).  When wine yeasts (s. cerevisiae) ferment grapes into wine, they expel tiny amounts of SO2 as part of their metabolism(1).  So young wines almost always have SO2 with levels typically from less than 10 parts per million (ppm) to more than 100, but typically it is less than 30 ppm.  

How much is a ppm?  To visualize 1 part-per-million, it is about 1 inch in 16 miles, 1 minute in 2 years, or 2.5 liters in an Olympic swimming pool. 

Wine yeast have evolved through the millennia to out-compete and dominate the other native microbes by excreting alcohol and SO2.  SO2 acts as an antimicrobial agent, however the yeast are not inhibited by these small amounts they generate.

Two Benefits of Sulfites in Winemaking

As an antimicrobial, SO2 can be added in the winemaking process to inhibit spoilage microbes and encourage the beneficial microbes: those that make our delicious wines.  Many wineries have modern practices that minimize the need for excessive SO2 additions.  These additions can range from none (in some organic wine), or up to the legal limit of 350 ppm in the United States(2).  But most industry members only need to add 25-35 ppm SO2 in order to maintain the quality.

One tool winemakers use to reduce the use of SO2 is to maintain a lower pH so the wine becomes self-preserving without excess SO2.  SO2 becomes exponentially more effective in higher acid wines like Sauvignon Blanc or Riesling (wines with a low pH)(3).  Another tool is filtration at the time of bottling so that the vast majority of microbes are removed before it is sold.

SO2 is also an antioxidant.  It sequesters compounds that prematurely age wines in a negative way.  Small amounts of SO2 added at bottling, even about 10 ppm, can add years to a wine's aging potential.

European Wines Don’t Have Sulfites: Myth

First of all I want to dispel a common myth that European wines have no sulfites. “Many” European wineries do add sulfites.  Not all, but many do. It is a common misinterpretation of the labels from Europe.  There is simply no European regulation that requires them to state “contains sulfites” on the label.   I am speaking of wines that are only sold IN Europe, not imported into the U.S.  

I’ve personally heard people tell me they don’t get headaches from Italian wine because they don’t add sulfites. There is a lot of confusion on this topic.

Why do most domestic wine labels have the statement “CONTAINS SULFITES”, whereas wines in Europe do not?  (Imported wines sold in the U.S. do indeed have the statement on the label).  This statement is a Federal TTB regulation for consumer protection.  But there is a historical reason for it in the U.S.:  The Salad Bar incident.  

Fast food restaurants back in the 1980’s were adding extremely high amounts of SO2 to keep the fresh vegetables from browning, estimated to be about 10,000 ppm.  That is like taking 200 aspirin tablets per dose.  It was done by inexperienced staff without proper training or instruction.  Over time 13 people died from excessive SO2 in these cases (see “Sulfites in the Salad Bar”(4)).

Laws were passed to stop the practice altogether in restaurants, but remained as a warning statement on wine bottles, even though the wine legal limits are exponentially less.  The United States is the only country in the world that requires this warning statement.

Organic Wines: Wineries that choose to add no SO2, like organic wine, can claim statements like “No Sulfites Detected” on the label among a few others(3).

Health Effects & Allergies

A true sulfite allergy is also commonly misunderstood.  When some wine drinkers complain of sulfite headaches, they most probably have a sensitivity to higher concentrations of SO2, or other compounds naturally occurring in grape wine, like histamines(5).

Let's discuss allergies first.  There are very few people that have allergies to sulfites.  Those who do lack the digestive enzyme sulfite oxidase and therefore cannot metabolize sulfites.  Our own bodies produce about 1000 ppm of SO2 every day as a part of metabolism.  Many people born with a true sulfite allergy have chronic issues or never even survive beyond the first year of life, because our own bodies produce much higher quantities than what is legally allowed in wine(5).

That brings us to sensitivity.  Some people are much more sensitive to white wines than reds, and some are vice versa.  So what is going on?  People that are sensitive to sulfites include people who suffer from asthma.  This is a very real and valid concern for those who consume wine containing higher levels of SO2.  It can actually be dangerous for those asthmatics in rare cases.  

For the majority of wine drinkers and wines, SO2 is barely or completely undetectable.  But is this really true?  It depends on the wine and the winemaker.  

In general red wines have and use less SO2 for long term stability when the tannins are higher (think Napa Valley Cabernet).  Tannin from the seeds and skins provide natural protection against oxidation (and aging).  White wines don’t have tannin, so sometimes winemakers add a bit more SO2 for protection against aging (think antioxidant).  But then again, some bright acidic white wines need a lot less SO2 for the same protection.  So it depends on many factors.

Final Thoughts on Sulfites

Sulfites in wine are a natural byproduct from fermentation.  It generally exists in minute quantities and, according to the FDA, is generally regarded as safe(6).  It has been used since the Roman Empire as a preservative that allowed wines to last and age while avoiding spoilage.  

The natural end state of grape wine is vinegar, unless humans intervene and provide methods of protection.  For thousands of years and with modern winemaking techniques, SO2 is still the best compound of choice that helps winemakers keep oxidation away from wine, and judicious use of minute quantities helps preserve the quality. Some winemakers claim it enhances freshness and fruitiness.

A final tip: sulfites are volatile.  If your wine is younger than about 5 years, open it and pour it while you splash.  Swirl it - not just to look fancy - there’s a purpose for the swirl.  Decant it and let it breathe a bit by exposing it to the air.  All these actions help dissipate the sulfites and aeration improves the aromas.

When we put these myths and facts in perspective when discussing sulfites as it relates to wine, we become better informed about the beverage we love.   


(1) Rankine, B.C. and K.F. Pocock. 1969. Influence of yeast strain on binding of SO2 in wine and on its formation during fermentation. J. Sci. Food and Agric. 20. pp. 104-109. Eschenbruch, R. 1974. Sulfite and sulfide formation during winemaking - a review. Am. J. Enol. and Vitic. 25:3, pp. 157-161.

(2) TTB Federal Code of Regulations: Title 27 CFR 4.22(b)(1)


(3) TTB Federal Code of Regulations


(4) The Washington Post


(5) The Regents of the University of California 2007,Lesson 7: Fermentation & Aging: Sulfur Dioxide (SO2) Topic 7.2: Health and SO2 Sensitivity

(6) Select Committee on GRAS Substances (SCOGS) Opinion: Potassium metabisulfite, sodium bisulfite, sodium metabisulfite, sodium sulfite, sulfur dioxide


What's on a Wine Label?

Do you know what a wine label must contain, and what are the basic requirements for wine producers?  Well even the most experienced producers don't always get it right.  That is why the federal government’s Department of the Treasury oversees and approves labels on most alcoholic beverages, including table wines.  The governing bureau is the Alcohol and Tobacco Tax and Trade Bureau, or TTB.  

So what is table wine?  There was a time when the term “table wine” was thought to mean jug wine or inexpensive wine.  But table wine is a classification used by government agencies to set and collect alcohol excise tax.  Therefore table wine is any wine between 7 and 16 percent alcohol.   This means a jug wine for $5 and a cult wine for $250 are both table wine, if the alcohol is between 7-16%.

Some wines that are not intended to be sold interstate can file for a label exemption, but they must have a statement stating “for sale in MA only” or the state where the wine was produced. Every wine producer must submit an application for label approval or exemption application to the TTB before it can be sold to the consumer.

The minimum information for a wine label

Proprietors of wine premises must label each bottle or other container of beverage wine prior to removal for consumption or sale with the following information:

The rules and requirements are complex.  If you are interested for more information, see the TTB site: https://www.ttb.gov/wine/7percentormore

How Many Servings Per Bottle?

A typical bottle of wine is 750 ml which contains about 25 fluid ounces.  The accepted standard glass of wine will have about 5 oz., so there are usually 5 servings or glasses per bottle.

Some people prefer a bit more and tend to pour a glass with 6 oz., which makes the servings per bottle just four, but this is not the accepted standard that is used, especially when estimating one's consumption of alcohol per hour.

When planning a dinner party or holiday gathering, the question is how many bottles does one need?  One can expect to serve about two glasses of wine per person, which is best enjoyed with a meal.  (Alcohol is consumed into the blood stream 40% slower when consumer with food.)  So a good estimate for entertaining guests is to have 1 bottle per couple.

The Winemaking Process: Overview

Rule #1: Keep everything clean and sanitary.

Rule #2: There are no recipes.

(These are my rule lessons from classes and empirical experience, which may differ between winemakers.)


The winemaking process can be as simple or as complicated as a winemaker chooses.  Every year's grape vintage can be as different as the weather.   It all depends on how the winemaker chooses to proceed and what style they hope to achieve. 

As my professor coined it, "winemaking is a sum of a thousand different decisions"(1) and no two wines can ever be the same.  I'll try to boil it down to the minimal general process steps.

Red Wine Process

White Wine Process

Generally white wine is made using the same Red process steps.  Except step 1 (Crush) is replaced with step 7 (Press) to squeeze out the grape juice before fermentation.  No skins are included in white fermentations (except "orange" wines). 

When bulk wine is moved from tanks or barrels, the term is called "racking".  Read The Winemaking Process: "Rackings"  to learn about why racking is important as a process step.

(1) Grady Wann - University of California - Davis - Wine Production Lecture

The Winemaking Process: Rackings

The transfer of the wine, called racking, is a gentle process with one main purpose: separate the clear wine from the sediment.  The sediment is called lees and has fermentation byproducts that are no longer desired, like the dormant and dead yeast cells, bits of grape particulates, and other natural microbes.  These microbes were responsible for making the wine and have given many positive qualities, but their job is finished.  

The First Racking

The first time a wine is racked, the majority of the lees are left behind and removed.  The yeast cells autolyze (or burst open) and provide anti-oxidant protection and polysaccharides which improve the mouthfeel of the wine. The wine is now bulk aging in oak barrels, where it will slowly mature for the next year.  At this stage the wine is still “alive” and can evolve because it is not pasteurized.

Why Use Oak Barrels?

Oak barrels have a way of maturing wines that no other vessels have matched.  Barrels act as an environment and are not simply used as a container.  The barrel and wine interact with small amounts of oxygen to orchestrate all kinds of chemical reactions that create new flavors, but these are very slow and it takes 6 to 12 months for many of them to form.

Many large wineries try to reduce their costs with inexpensive plastic vessels, or very large stainless steel tanks with oak adjuncts that can simulate the conditions of barrels.  The oak adjuncts, like sawdust or oak extract, reduces the time and price of the wine so it can be rushed into the marketplace.

Wine Cost

There is no match for the quality of the wine that has been given the time to age in oak barrels, which most boutique and prestigious wineries choose to do.  Barrels are very expensive ($1000 or more).  Aging wines in hand-coopered oak barrels can significantly enhance the complexity and flavor quality, when winemakers are trying to achieve certain styles.  This is one difference between a $12 bottle and a $24+ bottle of wine. Another main cost is the grapes themselves (a future topic).  

The Winemaking Process: Barrel Aging

Barrel Aging to Achieve Stability, Style and Complexity 

Have you seen a cloudy wine?  It generally indicates the wine is very young or not stable, had possibly spoiled, or was not allowed to properly mature before it was bottled.  Stability and aging are the topics of this discussion.

First: Stability

There are compounds in wine that form hazes and sediments that denature over time that lead to larger complexes.  If sufficient time is allowed for these reactions to occur during the aging of the wine, the particulate matter that forms can be removed using transfer techniques like racking. This reduces the need for clarifying additives, and allows racking to be the preferred clarification method. This is a gentle process that removes the unstable components and therefore the wine will be stabilized. Aging can be a means of achieving wine stability.

Next: Aging to Achieve Style and Complexity

When aging is done to add complexity, it may be done under conditions that add nuances to the wine, as with oak barrels. Allowing time is a way of aging to achieve style. New characters can be derived from yeast lees and oak when they are present during aging.

So aging in oak allows the formation of new characters, from oak cooperage and yeast lees, but the amount of complexity greatly depends upon grape variety and its chemical composition.  As new flavors develop, complexity increases. Thus aging can be used to subtract or add characters and to increase complexity. The increase in complexity can be considered as a multiplication effect. This is because a single compound can interact with several others, producing a spectrum of reactants. Some of the reactants can undergo further reactions, and complexity is greatly amplified. 

Small amounts of oxygen exposure during aging has some positive effects in red wines, but too much can be detrimental. Oxygen aids in reactions which can soften astringency and stabilize red wine color. These changes are critical to quality wines. The use of barrels means constant exposure to very small amounts of oxygen.  Winemakers need to periodically “top up” the barrels with extra wine to make up for the evaporative losses that occur with the porous wooden vessels.

Aging on yeast lees can be especially important in certain white wine styles, but red wines benefit too. Yeast autolysis (when cells burst open) adds flavor compounds into the wine.  This process also adds some anti-oxidant protection, and polysaccharides are released to add richer mouthfeel and help with the integration of oak characters, but it can take 6 months.

Finally, the size and toast-level of wine barrels have a strong impact on the style. Different from whiskey barrels, where barrels are shaped with steam and the inside quickly charred, wine barrels are bent using water over an open flame and once assembled, the inside is slowly toasted to bring out the vanilla and spice characters that we look for in our barrel-aged wines.  Surface area affects the reactions as well so larger barrels have less of an impact on the wine than smaller barrels because they hold more volume and have less contact with the wood.

What’s in the Bottle?

For oak-aged red wines, read the back labels.  Wineries that choose to spend the time and money aging their wine in barrels will often write the supplemental facts on their labels.  It's the only time they have the consumer’s focus on their bottle, and many will try to give the most important facts that make the quality difference.  

For stability, inspect the clarity by looking through the bottle and visually inspecting it.  Use an LED mobile flashlight to shine the beam through the bottle.  You can compare the visual beam in different bottles to know if it is slightly cloudy.  If you can see the beam, the wine has some particulates.  Cloudy doesn't mean “bad” if that was the winemaker’s intention.  Some unfiltered wines can turn cloudy after bottling.  Simply open it and enjoy it with a friend.

Integrated Pest Management

We grow our vineyard in an environment as natural as possible.  We employ organic and integrated pest management practices (IPM) like leaf removal in the fruiting zone to improve air circulation, have no till soils, and utilize cover crops like white clover to help keep the vines naturally nourished and healthy.  These practices reduce the need fungicide sprays.  

We also encourage native and beneficial plants like goldenrod, milkweed, dandelions and Queen Anne's lace (wild carrot) to attract a myriad of pollinators.  This attracts beneficial insects that help ward off pests.  We never spray insecticide or use any chemical weed killers in order to protect birds, pollinators, and the overall ecosystem.

Redox Potential for Quality Control

The winemaking process comes with many challenges.  One major concern to most winemakers is the generation of unpleasant aroma byproducts, like sulfides.  When these "reductive" aromas are not mitigated, they diminish the quality of the finished wine.

We employ advanced monitoring methods to help improve our red wine fermentations that we believe produce more aromatic and fruitier wines.  We monitor and control the reduction-oxidation (Redox) potential by pumping small amounts of filtered air into the fermentation environment, but only as needed in order to keep it less reductive. 

Why?  Generally, when yeast are at their peak of activity, they consume all available oxygen for their life-cycle processes and reduce the Redox to negative levels, enabling other natural chemical byproducts.  Some of these byproducts are considered detrimental to wine quality.  The main byproduct from low Redox levels is the natural generation of hydrogen sulfide (or H2S).  These compounds are a natural part of wines, but detract from quality when they are in excess.  

When we use controllers to monitor Redox levels and introduce filtered air, we help keep the fermentation in positive ranges and greatly minimize any excessive H2S byproducts.

More Information: This is a trend in the wine industry that we decided to follow.  Some major wineries in California have employed these same techniques at large production scales.  

Read more about the Opus One study: https://www.winebusiness.com/news/article/202368

Read more about the UC Davis lab: https://engineering.ucdavis.edu/news/wine-redox-boulton-nelson

Quality Impact with Small Batch Winemaking

Small batch winemaking is the process of making wine in quantities typically less than 500 cases. This type of winemaking is often done by independent winemakers who have a close relationship with the land and the grapes they use. 

Small batch winemakers have more control over the winemaking process, which can lead to wines with higher quality and more distinctive flavors.

Here are some of the benefits of small batch winemaking:

🔹 More control over the winemaking process. Small batch winemakers have more control over the winemaking process than large-scale winemakers. This is because they are able to make decisions about the grapes they use, the fermentation process, and the aging process. This level of control can lead to wines with higher quality and more distinctive flavors.

🔹  Greater attention to detail. Small batch winemakers typically pay more attention to detail, such as the temperature of the fermentation process and the amount of time the wine is aged. This attention to detail can lead to wines with more complexity and nuance.

🔹  More creativity. Small batch winemakers are typically not bound by the same ​restrictions as large-scale winemakers. This gives them more freedom to experiment with different grape varieties, fermentation techniques, and aging methods. This experimentation can lead to wines with more unique and interesting flavors.

Overall, these benefits can lead to wines with higher quality, more distinctive flavors, and greater creativity. If you are looking for a wine that is truly special, then seek out boutique wineries that produce small batch wines.