Monday, November 12, 2007

Heating and cooling your wine

The past two weeks have seen rather low temps at night, which have slowed my ML fermentations down quite a bit.

Harvest is when my energy usage is at its peak, most of it going into cooling during the early part of harvest, which then turns to a need for heating at the end of harvest. A winery’s heating and cooling is generally the lion’s share of the total energy usage of any winery.

Because of the amounts of CO2 that are generated by fermentation, remote operated fans are constantly flipping on and off drawing out the invisible gas and replacing it with breathable air from outside the winery. At the start of harvest, that outside air is usually pretty warm due to our Indian summers, and that has a tendency to cause the ferments to spike temps upwards…which of course, speeds up the fermentation, releasing more CO2, thereby needing more exhaust, etc…

It’s a vicious circle: on the hottest days, you pump out your coolest air (replacing it with hot air from outside) to make the cellar a safe place to work while simultaneously causing the ferments to pump more CO2 into the cellar. Nighttime temps are still relatively warm at the start of harvest, but cool enough to moderate the ferment speeds, so much of the cooling is attempted by drawing in air at night – a great strategy in cool coastal areas, or an area where fog is common.

In the cooler harvests, we see the opposite with exhaust fans drawing in a large amount of cooler air and retarding the ferment speeds, and that might keep us from extracting as much flavor and color from our red fruit as possible. Warming is our task here, and the need for exhausting gasses puts all our warmed air out into the environment instead of keeping our ferments going strong. But higher spikes can cause problems for both yeasts and bacteria and may cause “off” flavors to be formed in your wine. Usually, we’re looking for our white ferments to stay in the mid 60’s (°F) and our reds to be mid 80’s - the higher temps for red are needed to extract the cooler and tannins properly. The Primary ferment (the conversion of sugar to CO2 and alcohol) causes much more heat to be released than the Secondary (ML) fermentation does, and that’s reversed from our needs for heating, as the Primary happens when its warmer, and the secondary when the weather has cooled quite a bit.

Most times we need the wines to finish with the ML ferment before we can add SO2 and stabilize the wines…and that is sometimes delayed due to the ML bacteria needing higher temps to work to completion. Since this fermentation happens when the nighttime air we draw in is quite a bit cooler, we generally need to heat at this point.

Ways to create wineries which are more energy efficient are well known, and include the above mentioned passive cooling of night air, insulation for any tanks which are outside – as well as the buildings, and possibly using a cave to keep the wines cool.

Many more wineries are exploring solar panels to help them offset the energy needed for production, and that is buoyed by the wineries which have already installed them and have good results. It’s a good time for creating a new winery since technology has progressed, and even for retro-fitting an older winery to make them more efficient. And the press for "greening up" your operation has never been better...

A true win-win situation for all.

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Anonymous Wine Scamp said...

Not to display a shocking level of ignorance, but is there a way to vent the C02 coming out of the fermentation vessels directly? Stovepipes going straight outdoors, or something? I've never seen that in a winery, but reading your post, it seems like a good idea...

Thanks for an interesting write-up of a complexity to fermentation that seriously never occured to me! Really enjoyed it.

November 12, 2007 10:19 AM  
Blogger St. Vini said...

Wine Scamp,
I'm afraid stovepipes or some ducting like that wouldn't really be feasible...
Outdoor cellars have been employed since mankind started to purposely ferment fruit for wine, and that would solve that problem but then you have to deal with diurnal temp fluctuations and seasonal fluctuations as you cure one problem by trading it for another.

The cooling weather after harvest is over as we move towards winter has a tendency to kick the ML bacteria in the teeth -seriously slowing down the rate at which it completes- and historically that is what gave way to the term "secondary fermentation"...
The juice would vigorously ferment through the sugar and then fall quiet for the winter when it was cooler. In the springtime, warming weather would "restart" the fermentation process by making the bacteria active again, and the "finished" wines would get cloudy, start to bubble and seem to ferment a second time.

These days, we'd rather see this happen earlier in the cycle -preferably right after the primary fermentation- so we can add SO2 to the wine & help keep it from spoilage.

All that said, I still feel that there's a lifetime worth of patent royalties for the person who can come up with a way to capture & purify the CO2 gases which are released during fermentation. There's a big enough market then selling that captured CO2 back to the wine industry to gas tank headspaces, or other industrial uses, etc, to make the idea lucrative...once it can be captured, that is.

Thanks for the comment,

November 13, 2007 5:00 AM  
Anonymous Wine Scamp said...

Yes, it would seem that someone should be working on this CO2 capture idea even as we type...

Thanks for answering my question!

November 14, 2007 10:39 AM  
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