MW Topic of the Week: Temperature in Winemaking

Hello!

This week, we're back in Paper 2. Many Paper 2 essays can include direct or indirect calls to discuss the effects of temperature. So this week, I've selected the following question:

Temperature management is the key to modern winemaking. Discuss. (2017)

Uh oh, a black hole question for me! I get a bit over excited when responding to these technical questions. For me, this can lead to responses that get bogged down with details that are accurate but not always the most situationally relevant (see: anything I write on sulfur dioxide). To focus our study this week, I read through the examiner's report and found some guidance for tackling the question.

  • We need to discuss all the main winemaking stages - harvest, fruit storage/transport, processing, fermentation, bulk storage/aging. We could write a full essay on fermentation temperatures and forget to discuss the others.
  • Better papers were structured in the chronology of winemaking.
  • We need to provide temperature values. Ranges like 10-16°C may be seen as too broad.

Does anyone have a winemaking stage that they would like to discuss? Does anyone have specific examples for producers, temperatures, and why they select (or don't select) those temperatures?

Thanks for studying with , and I!

  • can you talk a little bit about how temperature at pick time affects quality? Like why some producers insist on nighttime picks, especially for fresher styles of wine? I'd also love for you to explore temperature and ester formation in the fermentation process.

  • Hi Sabrina and Team,

    I started to think about this question and since it is a Paper 2 question I think the focus is from GRAPE RECEPTION (so excluding harvest and transport) through the end of MLF (again excludes bulk storage and maturation). Am I wrong here?  Given we only have an hour to crank these out, I have been advised that bounding the question is paramount, so checking my understanding with the team. 

    I also feel there is a pitfall here if one doesn't define "modern winemaking" before launching onwards.  It is a pretty loose term meaning everything from clean, precise, fault free and consistent to extracted, oaky, fruitbombs, lacking a sense of place.  In the context of this question the former seems logical, but probably worth spelling out, right?

    I am wondering if the focus should just be control of pre fermentation holding period temperatures, fermentation temps, and any post fermentation holding temperatures through MLF, or designed to avoid MLF.  Looking for feedback on my reading of this before I go further.  Thanks, as ever. 

  • Hi Anne!

    I totally agree that we have to set the scope before we dive in. I read through the Examiner's Report and they specifically mentioned "fruit storage" - which I'm interpreting as transport to winery. They also mentioned bulk storage so I'm putting my bound on those sides.

    But I'm at a bit of a loss for "modern winemaking" because it is so loose. Maybe a simple definition of commercial wine produced in a certain time period (NOW)?

  • It is confusing.  I think fruit storage could be in the winery after transport.  I visited several Chilean Pinot Noir producers who held the grapes cold for at least a day before the cold soak started,  I looked at the examiners reports too and was still not clear.  I will take a shot at the whole period you detailed.  

    As for definition of "modern winemaking" an approach focused on purity of fruit, aromatic expression and fault exclusion through the use of technology and innovation. 

  • OK so RE fruit storage... I can't quite remember but I believe it was Ch Ste Michelle that has chosen to machine-harvest their Riesling despite some potential downtick in quality specifically because that means they are able to harvest at night, which more than makes up for it. I also recall a Greek producer (again, can't remember which -- I need to dig through my old notebooks!) saying that, as it's pretty warm when they harvest, they store their fruit overnight in a "cold room" in order to get the fruit so that it will start the fermentation process at a lower temp. 

    Then there is cold-soaking. Many producers who both employ cold-soaking and native yeast will let cold, night-harvested fruit slowly warm up and start fermenting. I believe a cold soak happens in the high 40s/low-mid 50s and that fermentation won't really kick off on its own until at least the high 50s but at least the 60s? Are these numbers close?

    I also know fermentation temperatures tend to be higher (around 90 is often common) in reds, and lower (60s?) for whites. That said, there are always exceptions. Heitz ferments their Cabernets at super low temperatures because they don't want too extract too much tannin. And I know some winemakers ferment "non-aromatic" whites at higher temps than aromatic or floral whites because the lower temps preserve the delicate and easily broken-down esters. 

    Also during fermentation, too cold or too hot temps can cause stuck fermentations and extreme heat can even kill the yeast. Again, don't have ranges handy.

    Following primary fermentation but prior to pressing, I've seen more than one producer wrap an electric blanket around their (albeit small and wooden tanks), in order to elongate tannins. This was specifically for Sonoma Coast Pinot Noir.

    Malo likes some warmth, too. That's why in Burgundy where the cellars are super cold in the winter malo generally doesn't kick off until well in the spring. In California some cellars or caves come with "hot rooms" where they can wheel barrels in order to kick start malo.

    Low temps can also help avoid microbiological issues. For example, in my brettanomyces article (shameless plug!) I interview some winemakers who keep their barrel cellars lower temp during elevage in order to stave off or stall any brett that might be present.

    Additionally, wine can absorb more dissolved oxygen at lower temps, so I know some producers won't bottle their whites in the winter so as to not pick up excessive DO on the bottling line.

    Also, in general, I think that high temps speed up or enhance both extraction (color, tannin, oak, etc), microbiological and oxidation. 

    Do you think it is worth talking about flash pasteurization and cryo-extraction?

    Sorry this answer is so rambly and vague, I'm tired.

  • I’m so tired! Sleeping 

    I’m going to incorporate these rambly ideas into my response in the next few days. I’m having a text conversation with a winemaker at 25k ton facility which employs must heating/chilling and standard set points on their tank chillers. I’d like to get us some hard numbers. 

  • At a winery I used to work at, there was one batch of wine that got so hot, due to a wild fermentation, that wine was coming out of the top of the stainless steel tank. 

    Which pushed us back about 5 hours when we were hoping to take down nets and tie up another layer of nets so that harvest could start bright and early. 

    Can you expand on what you mean by elongating tannins? Are they looking for the tannins to last longer?

    Also, I have been trying to come up with a question to broach the subject of dry ice. I am not entirely sure if it is relevant to this topic. However, I saw over the weekend that Daou(?) was adding dry ice to one of their tanks of sauv blanc to put off the start of fermentation so it got me thinking about how often dry ice is used, when it is used, and if there are any negative side affects to using dry ice. 

  • Hi Adam!

    I've had a similar experience with some native ferments - we've had thunderous ones that roll their own cap and go sugar and malic dry very quickly.

    For elongated tannins, I think Kelli means "polymerized". This is when the small and slightly bitter tannins bind together into an elongated chain. The result is a smoother and richer texture.

    And I use dry ice! I think it is relevant to this question because it is a tool that smaller wineries can use to manage heat. At our winery (College Cellars of Walla Walla / Institute for Enology and Viticulture) we mainly use dry ice to keep air off of delicate juices or grapes. However, it also serves the double function of cooling fruit or juice so that oxidation reactions happen more slowly. I don't believe that there are many negative effects of using dry ice. However, many producers may not want to keep air off of juices/musts or may want to keep lots warm so that they're ready for inoculation.

  • I tried to contrast a warming to each cooling example. night harvest I stated alone and said it might be considered winemaking, but contrasted cold transport with a calculated warming to start ferment just as juice arrived at facility, cold storage vs a drying and warming of Randal graham, cold soak vs flash detente. cool ferment in Marlborough suav blanc vs heat spiked at rippon to blow off primary aromas. cool Malo vs warm to express more or less diacetyl . cooling at winter to stop Malo and get better color set, vs warmed stuck ferments and warm rooms for Malo starters. cold room storage vs a tuscan producer that wants ambient storage as part of imparting terroir. I know its more part of QAQC but I mentioned cold stabilization and protein stabilization. 

  • Thanks Sabrina!

    So the tannins are going from a clunky or disjointed tannin to a smoother tannin?

    Thank you for the insight for the dry ice! I would think wineries/producers would more than likely want to avoid any spoilage or oxidation. Is there a general ratio that is followed or do you just eye ball it?

    Lastly, how do you do tartrate stability? I know at the winery I worked at just did the traditional cold stabilization so I am interested if you do something different.

  • I like this compare/contrast method. It makes sure that you show both sides and lots of perspectives!

  • Hi all

    I have “harvest brain” and it took me way longer than I’d like to produce this response. This “essay outline” is leaning towards “semi-organized ideas”. For an essay, I would work to include linking language in each paragraph - I’ve got ideas, but I know that they need a sentence to link them to “modern winemaking”.

    Introduction (template)

    Restate the question: Temperature management is the key to modern winemaking. 

    Short justification: Temperature influences microbiological growth, microbiological flavor production, and reaction rates both positive and negative. Control of the winemaking process is key for modern winemaking.

    Scope: This essay will address winemaking stages from fruit transportation through raw wine bulk storage.

    Definition: Modern winemaking is defined as wine production for the international market in the 21st century.

    Fruit storage/transport

    I’m going to discuss fruit transport instead of storage because I don’t have any firm producer examples for storage. If anyone can give one, please comment!

    • If fruit is machine harvested, must oxidation can set in quickly. Microbes can thrive in warmer conditions, and abiotic reactions will occur more rapidly in warmer conditions as well. Fruit harvested at night will have the lowest possible temperature that can be achieved without refrigeration. The large thermal mass of cool, machine harvested must will help to keep the must cold during transportation to the winery. This serves to minimize the risk of oxidation and/or spontaneous fermentation.
    • Example: Ste Michelle Wine Estates in Washington, USA machine harvests almost all fruit. Transport times can be be up to 3 hours from vineyard to winery with daytime temperatures over 25°C. Harvesting at night during temperatures closer to 10°C keeps the must cool and stable during transport.

    Processing and Pre-Fermentation

    The same microbiology and oxidation principles are at play during processing and pre-fermentation cold soak. 

    • For an effective cold soak, temperatures should be below 10°C to limit native fermentation.
    • At this stage, the dominant yeast may be Hanseniaspora and there is potential for volatile acidity production if fermentation is native and unintentional.
    • However, cold soak with temperature climb may be employed to let cold, night harvested fruit warm up to for native fermentation or inoculation with cultured yeasts. (Kelli, your numbers are close. I like saying 10°C for cold soak and 20°C for inoculation because they’re close and easy to remember!)
    • Does anyone have a specific producer for cold soak? Something Burgundian?

    Thermovinification and flash detante and modern techniques for color, flavor, and tannin extraction. Must is heated to over 80°C and subsequently chilled. 

    • Example: Frescobaldi in Tuscany, IT uses thermovinification on Pinot Noir and Sangiovese. However, they only utilize it for a small portion of the production because it highly increases extraction but minimizes varietal character.

    Fermentation

    • For red wine, temperature is the main factor affecting phenolic extraction. Higher fermentation temperatures (between 30-35°C) result in greater color and tannin extraction. This is similar to brewing tea - the tea extracts quickly in boiling water.
    • Example (stolen from Kelli): Heitz Cellar in Napa, USA ferments their Cabernet Sauvignons at lower temperatures to minimize phenolic extraction on ripe and phenolically concentrated fruit.
    • However, unchecked fermentation temperatures can result in stuck fermentation due to excessive heat. Temperatures over 37°C can result in yeast cell death.
    • Yeast lipid metabolism is strongly affected by fermentation temperature. Therefore, temperature will impact a wine’s aromatic potential, especially in white and rosé wines. It was traditionally thought that cooler fermentation temperatures impacted ester formation. However, according to Scott Laboratories, this is no longer credible. Slightly warmer (in a white/rosé context) temperatures of 16-20°C have maximum ester production.
    • Example / counter point: DuMOL in Sonoma, USA ferments Chardonnay 15-25°C. This is not “managed” via refrigeration and is a result of yeast heat production in cool cellar. The temperature range is naturally produced.

    Malolactic Fermentation

    Malolactic fermentation is performed almost universally on dry red wines and is common in some full bodied whites. In modern winemaking, malolactic fermentation is intentional or blocked. Temperature plays a large role in the promotion or blocking of MLF.

    • MLB have an optimal growth temperature between 15-30°C. 15°C is warmer than most ageing caves.
    • Example: in Burgundy, some winery caves become too cold for immediate MLF during the winter. MLF is not blocked, but may be delayed until spring. MLF is still intentional, but temporarily inhibited by temperature.
    • Example: Does someone have an example of a winery with a warm MLF room? I’m trying not to mention College Cellars or Ste Michelle Wine Estates too many times.

    Bulk storage/ageing

    Similarly to pre-fermentation processes, temperature management post-fermentation impacts microbial activity and abiotic reactions.

    • According to Scott Laboratories, higher post-fermentation temperatures can result in loss of delicate aromas. This includes the degradation of terpenes which are signification varietal character aromas in Muscat, Torrontes, and Gewurztraminer.
    • Cooler barrel cellar temperatures will also suppress microbial growth, most significantly, the growth of Brettanomyces. According to research from Washington State University, only one third of Brett strains can grow at 10°C and their growth is very slow. 

    I cut off here because I think the post-storage processes fall under P3 (and I didn’t see them mentioned in the examiners report).

  • Just for you ;)

    Background: the fatty acids in yeast cell membranes and their subsequent metabolism play a large role in ester formation. Imagine the membrane like fats that you cook with - butter is a solid at room temp but olive oil is liquid. If the fermentation temperature is cold, the yeast change their membrane fats so that they stay "liquid" (more olive oil, less butter). Same principle applies in the opposite direction (if the kitchen is hot, the butter will melt). Different fat, different flavor.

    Previous research has indicated that there was higher ester formation at cool temperatures. However, I just read a post from Scott Laboratories from 2018 (the latest thing I could find). They say that current research indicates that ester formation is higher in slightly warmer ferments (16-20°C) and this is accounting from loss due to the esters being "blown off" by a more bubbly/vigorous fermentation.

    Learn something new every day!

  • I think the vast majority of small to medium sized producers in the US are doing traditional cold stabilization, potentially seeding with cream of tartar which speeds up the rate of crystallization (though this seems uncommon). I'd think some larger wineries are using some of the more high-tech techniques. Enartis (wine supply company) recently released a new additive (called Zenith) that can be used for cold stabilization. It's basically another salt that keeps tartrate crystals from forming. I don't know anyone using it, but it's inexpensive (whereas refrigeration is expensive) so I'd guess some people will use it on inexpensive wines to cut costs. That said, most winemakers I know aren't too keen on unnecessarily adds. 

  • Chateau Fieuzal in Pessac and Realm Cellars in Napa store their fruit in cold storage overnight to lower the temperature prior to processing. This also helps with logistics since the precise tonnage of fruit is unknown until it's been picked. 

    I'll also throw out that MANY wineries in Napa harvest at night. I know it's common elsewhere too, but most picks start early enough to ensure that picking is finished by 9am or 10am (so, often starting between midnight-3am.) You could use almost any place there as an example as it is a big cultural norm.

    The place I worked in Burgundy, Domaine Bitouzet-Prieur did an interesting version of a cold soak. Our tanks didn't have refrigeration, but we did have a heat exchanger tank, so every day, we'd pump the entire liquid contents into the heat exchanger, chill it to 10C, and put it back (like a rack and return). The cold soaks were long, roughly ten days. We had very high levels of ethyl acetate prior to fermentation but most of it blew off by the time fermentation was finished.

    It's also worth mentioning that cold soaking can be used for logistical reasons. When a cellar is very busy, it helps the winemaker control the timing of fermentation to make sure that there is enough bandwidth for management during fermentation.