Evidence for Damaging Effects of Heat Exposure on Wine During Transport and Storage and Recommendations for Protection

It is well known that long term heat exposure is detrimental to the quality of wine, specifically its sensory characteristics and ability to age.  Excessive heat can also alter a wine’s physical and chemical stability, such as showing a cloudy or brownish appearance and leaking bottles.  To date, most of the evidence for the damaging effects of heat on wine storage is anecdotal, with very little concrete scientific evidence backing up the claims.

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A bottle of wine being transported from winery to consumer risks many abusive shipping processes along the way, including excessive heat exposure.  This risk is exacerbated at times by high shipping costs, limited availability of refrigerated shipping containers, and general ignorance.  Many winemakers have even adjusted their production techniques in order to protect their bottles of wine from heat exposure, including deliberately oxidized and fortified; red wines that underwent extended maceration; and distilled wines.  Nearly all commercial white wines are heat stabilized during the winemaking process, so that heat exposure does not result in a visual change in the wine (haziness).

Even if heat exposure doesn’t damage the wine per se, the ageing characteristics will be changed following a certain time of elevated temperatures.  Specifically, heat exposure can prematurely release glucose-bound flavor precursors, decrease the levels of protective free sulfur dioxide, and cause an increase in browning.  The sensory character could be changed as well, though due to rapid heating and specific reactions of the many compounds in wine, it’s not certain that the “ageing” due to increased heat exposure would be the same as if that wine were aged for a comparable amount of time at a more traditional storage temperature.  It is likely that at least the subtle differences attributable to terroir would be lost.

One potentially hazardous consequence of increased heat exposure to wine while in storage is the formation of ethyl carbamate (EC).  Based on experiments with rodents, it has been shown that there is a probability of a carcinogenic effect of EC in humans when exposed to high concentrations of the compound.  In wine, EC is formed from its precursor, Urea, which is naturally present in wine from 100μg/L to 100mg/L.  Urea can be released by wine yeasts during or at the end of alcoholic fermentation, which then can spontaneously react with alcohol to produce EC.  This reaction between Urea and alcohol to make EC has been shown to accelerate exponentially when excessive heat is applied.  Therefore, excessive heat during storage of wine is a great concern.

The study presented today used EC levels as an indicator of wine quality in order to demonstrate the chemical changes that occur in wine during transport and storage.  The goal of the study was to provide wine makers and producers with information on how to properly handle their wines in regards to transport and storage as they work with transport companies, distributors, wholesalers, and retailers in order to minimize the exposure of their wines to excessive temperatures during this transitional period.

Methods

The wine used for this experiment was a model wine, containing 10mg of urea, 5g of potassium bitartrate, 3g L-malic acid, 1.1g potassium monohydrogen phosphate, and 150mL ethanol, brought to volume by adding de-ionized water.  The resulting pH was 3.5.

Temperatures were tracked and recorded using Dickson SP100 dual-channel temperature data loggers.  An internal temperature sensor recorded the air temperature inside the test package, and an external thermistor was placed inside a wine bottle filled with de-ionized water.  Temperatures were recorded every 15 minutes.

The test packages were created by loading a standard 12 bottle case with one bottle of model wine, one bottle of de-ionized water containing the thermistor, and the rest of the case fitting the data logger.

Test packages were shipped via truck or rail, in standard non-refrigerated containers with non-insulated walls.  Wine cases were assembled onto pallets, with the top of the pallets covered with thermal blankets (fabric quilts or plastic/metal bubble wrap) for insulation.

Test packages were placed in the shipping container in three different positions per shipment: one above the thermal blanket, one in the front of the pallet below the blanket, and one in the back of the pallet below the blanket.

There were 26 individual shipments containing a total of 47 test packages monitored in the summer and fall of 2000 during 13 different shipments throughout the US.  Wines were shipped via truck or rail from winery warehouses in California to wine distribution centers in Georgia, Texas, New York, California, New Jersey, Illinois, Florida, Missouri, Louisiana, and North Carolina.  Upon arrival, test packages were removed from their pallets and returned to California via USPS Priority Mail for chemical analysis.  Wines were in transport for a total of 1 to 3 weeks.

Upon return to California, wines were sent to ETS Laboratories for chemical analysis.  EC was analyzed by gas chromatography and mass spectroscopy.

Heat exposure of wines was calculated by integrating the temperature data for each 15 minute intervals and comparing them to ideal cellar storage conditions.

Results

  •       Temperatures ranged from -13oC to 44oC in the top (unprotected) position.

o   The freezing point of table wine is -5oC.

o   Volume expansion of table wine from 13oC to 44oC is 0.9% or 7mL per 750 mL bottle.

o   Normal headspace volume at bottling is between 4 and 7mL.

  •       There was a 2 to 4oC temperature difference between the temperature of the air in the storage space and the temperature of the liquid inside the bottle.

o   Therefore, the heat capacity of the glass protects the wine from short-term temperature spikes.

  •       Temperature changes during 1 day in the unprotected top position ranged from 4oC to 21oC.

o   This temperature fluctuation could result in significant volume expansion of the wine which could affect the structural integrity of the closure and glass.

  •       There were significant temperature differences between test packages, depending upon where in the container the test package was located.

o   All extreme temperatures occurred in the top location that was unprotected; indicating that wine shipped without additional protection (i.e. blankets) will be more prone to extreme heat exposure and variation between bottles in a single shipment.

  •       EC formation in model wines was found to be between 2 and 94 μg/L during the shipping period tested.

o   This resulted in a 10-fold increase in reaction rate every increase of 19oC.

  •       Heat exposure to the wines significantly increased the effective bottle age and wine shelf life.

o   The true age of the wine jumped forward by 18 months (1.5 vintages).

o   This accelerated aging will likely lead to different wines in terms of sensory characteristics than what they would be under normal aging conditions.

Conclusions

The results of this study showed that extreme heat exposure has potentially damaging effects on the stored wines.  However, current commercial shipping technologies can be sufficient in protecting wines against heat damage, as long as certain rules and procedures are applied each time.  For example, the use of insulation in shipping containers is critical in protecting wine against excessive heat.  Since wine bottles are heavy, they are usually packed at the bottle of the shipping container, which leaves a good amount of headspace above it.  As this study showed, the headspace is prone to excessive heat fluxes, so by insulating the shipping containers, this increase in temperature of the headspace can be hampered.

One concern about these protective measures is that the cost is too much to bear for wineries.  According to the authors of this study, the additional cost for different transport options, including special refrigeration units or protective blankets, usually adds no more than 0.1% to the production cost of even the most inexpensive wines.  Those red wines that are heavily extracted and considered to be very precious are actually the ones that are least apt to be damaged by heat exposure, due to their high abundance of protective phenolic compounds.

One part of the system that this study did not cover that could cause significant damage to the wines due to heat exposure is the time when wines are moved from small un-insulated delivery trucks to the consumers’ doorstep (or some other similar end of transport situation).  There isn’t too much that can be done at this point, other than packaging the wines in protective/insulating case boxes and not shipping during the hottest months of the year.  Overall, however, damage to wines caused by excessive heat exposure can be avoided mostly by ensuring proper protection in the shipping containers during transport and storage.

One thing I’d like to see a similar experiment with actual wine instead of model wine.  Since “real” wine contains many more compounds than the model wine in this study, do the chemical reactions therein change how the wine is affected by the heat?  The authors alluded to the fact that a heavier wine with higher levels of phenolic compounds would suffer less than other wines, so it would be nice to see this backed up with some data.  Also, were the EC fluctuations found in this study enough to be harmful to humans if consumed?  Or did the levels remain below any sort of threshold level?

I’ve love to hear what you all think about this topic.  Please feel free to comment below (no html tags, please).

Source: Butzke, C.E., Vogt, E.E., and Chacón-Rodríguez, L. 2012. Effects of heat exposure on wine quality during transport and storage. Journal of Wine Research 23(1): 15-25.



I am not a health professional, nor do I pretend to be. Please consult your doctor before altering your alcohol consumption habits. Do not consume alcohol if you are under the age of 21. Do not drink and drive. Enjoy responsibly!

12 comments for “Evidence for Damaging Effects of Heat Exposure on Wine During Transport and Storage and Recommendations for Protection

  1. Tony
    May 17, 2012 at 3:20 am

    Great study. If you would like to do some further commercial research, we would be happy to provide you with some real world test samples. We ship in protective packaging beginning right about now. Last year we had a total of 2 heat related complaints across thousands of shipments.

  2. May 22, 2012 at 3:10 pm

    Thanks for your comments, Tony! Unfortunately, I do not have the means to conduct any research on my own, but feel free to contact the authors of this study (just look up the study abstract and you'll find their email addresses). Cheers!

  3. June 16, 2012 at 12:49 am

    Becca, I'm very interested in this topic. I am not surprised to read that most of the evidence is anecdotal while we "all know" (have tasted) the detrimental effects of heat on wine. I'm glad to read of at least one study. I am a total stickler when it comes to storing wine properly and having it shipped properly. As a wine reviewer, I am often dismayed that samples come in less than desirable packaging and I know the wine is not what the winemaker intended me to taste. I have also seen wine lovers who poo-poo that heat is a big deal. That drives me crazy. More studies are needed and at least this study should get out to consumers and those few distributors/importers/grocery stores who think storage doesn't matter to the degree that it does.

  4. June 18, 2012 at 1:15 pm

    Thanks for your comments! I agree with all your points, and I'm happy you shared the post on Facebook to help get the word out about the topic!

    Related to the topic: I was moving out of my apartment this weekend, and I'd taken my nice wines out of my wine refridgerator so we could move that over. Someone had brought some of the wines outside to sit there by the truck and I nearly flipped. At least wait until the last minute to bring them down to the truck instead of letting them hang out in 80+ degree weather! Geez! ;)

  5. jan
    July 22, 2012 at 6:16 am

    In opening a case of foreign import wine, one bottle was found to have wine slightly oozing from the foil. We assumed heat exposure. Does this mean ALL of the bottles in the case are damaged even if the corks seem hard and no leakage is found?

    Thanks!

  6. July 24, 2012 at 2:11 pm

    Hi Jan,

    Was the cork pushed out of the bottle a little bit? When exposed to high temperatures, the cork can expand, which would result it is possibly being pushed out of the bottle a little bit. If it is just oozing but the cork is still in it's appropropriate place, the leaking could be due to other things, such as a faulty cork (which would only be a problem with that one bottle, and not the rest).

    I wouldn't toss out all the bottles in that case, but you may want to open one to taste it, if you can!

  7. November 15, 2012 at 11:51 am

    Becca, although the term “extreme heat exposure” is used in the article, what about fluctuating heat? What if cases of wine are exposed to 80F to 60F daily for a few months? Can you verify for me that this experiment points towards that or your other research shows this? Thanks!

    • Becca
      November 15, 2012 at 3:06 pm

      Thanks for your question/comment, Alana!

      I found this really cool article that came up with a mathematical model that predicts the new shelf life after wine was exposed to 20oC heat and 40oC heat (68F to 104F). It didn’t actually look at temperature fluxes, but it was certainly a starting point.

      They found that at 20C, the time to reach a critical level of SO2 in the wine (i.e. wine going bad) was 59% of the ideal storage shelf life. The time to reach a critical level of browning in the wine at the same temp was 38% of the ideal storage shelf life. At 40oC, the situation is even more dire. The time to reach a critical SO2 level at this temperature was 23% of the ideal storage shelf life, and the time to reach critical browning in the wine was only 8% of the ideal storage shelf life!

      So, just by leaving your wine at 20C, if it originally had a shelf life of 10 years, it would be reduced to 4-6 years (I’m rounding a little). By leaving the same wine with the original shelf life of 10 years at 40oC, the shelf life is reduced to 10 months to 2.3 years! For a wine that’s meant to be consumed young (let’s say a 2 year shelf life), it’ll go back by 9 months to 1.2 years at 20C, and as quickly as 2 months to 1/2 a year. This model isn’t perfect, however, since it was based off of results in the existing literature at the time, which were few and far between (I think it was based off of one type of red wine). More work certainly needs to be done to fine-tune the model, but long story short: higher temps = bad.

      Since your question was really about temp fluxes, I suppose I should give an answer related to that ;) At higher temperatures, the wine can expand if warm enough such that it can seep around the outside of the cork. Then, as it cools back down, the wine condenses and draws air down into the bottle with it, thus speeding up the oxidation process. Coupled with the fact that the wine is being damaged at the higher temperatures for other reasons (see above), the shelf life of the wine will be drastically compromised.

      There is likely a lot more to this story, and you’ve inspired me to dig a little deeper and write a whole post about it!

      Stayed tuned in the next couple weeks and I’ll hopefully have more answers for you!

  8. August 23, 2013 at 6:51 pm

    Great study! I would favor labeling that includes a temperature sensor that displays the minimum and maximum temperature that the bottle has been exposed to. Granted, the dimension of how long the exposure was at any adverse temperature would be more difficult to capture, but a sensor against the bottle would at least capture the max/min temperature of the wine, and would go beyond the shipping environment to capture how the wine has been stored until opened…

    With mass production, a color-coded temperature-sensitive label could be produced that would only add a few cents per bottle.

    • Becca
      August 27, 2013 at 1:51 pm

      Thank you so much for your great comments! Very insightful! Cheers!

  9. Mark Temple
    December 28, 2013 at 2:04 pm

    Over ten years or more, I have drunk countless bottles of wine brought back from S France to the UK in summer in a normal car, parked in the sun at times. The only case where I have doubted the wine has been in good condition has been a case of already oldish champagne.

  10. January 20, 2014 at 2:53 am

    A color-coded temperature-sensitive label is a great idea! It would be easier to decide whether transportation conditions are sufficient.

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