How hot will ferment get

Michael,

Fermentation temperatures are difficult to predict. Heat production depends on fermentation rate, the sugar available, etc. About 0.14 calories are produced by each gram of sugar fermented.

Heat lost depends on the fermenter (size, shape, material), ambient temperature, cap management, carbon dioxide gas evolution, etc. In general, the larger the tank, the higher the peak fermentation temperature.

Sixty gallons is a relatively small fermentation, and heat will be lost nearly as fast as heat is produced. If you have a fast fermentation, I suspect your temperature might reach 75 degrees. See Amerine, "Table Wines," page 374.

lum

I don't think you'll have any problem - either with runaway temperatures or too cold. Just be sure not to overfill your fermenters. About 400 pounds in a 60 gallon drum is ~2/3 full, and that's just about right. As for holding 90+ degrees for several days, forget it! The temperature may _peak_ over 90°F, but the reaction rate speeds up as the wine warms, so it tends to quickly run out of "gas" at elevated temps, and it'll cool right back down.

Tom S

Thanks Lum. Any ideas on how to raise the temperature by 15 degrees?

I guess I'm still a bit concerned that the fermentation by itself won't raise the temperature 25 degrees over the ambient temperature in such a small fermentation vessel. BTW, I also have the option of fermenting in neutral oak which should hold the heat a bit better. Do you think that fermenting 40 gallons in a 60 gallon oak barrel (sans top) has a better chance of rising that much?

...Michael

A 60 gallon drum isn't really that small a thermal mass. It'll get pretty warm in there!

BTW, I also have the option of

I wouldn't bother with fermenting in neutral oak. The temperature difference won't amount to much, and oak is a lot harder to sanitize than plastic.

Tom S

Someone needs to tell this to T. Mondavi. Here's an excerpt from an interview by WBM back in July of 2001:

Oak by virtue of its temperature holding properties, will allow for fermentations that give off heat to come up to temperature. Once fermentation is complete, the oak by virtue of being a highly insulated material will retain that temperature for a much longer period of time in a gentle fashion. As a result, some of the activities of extraction will be promoted better at a warmer temperature than a colder temperature. There is more development of the tannin structure, more subtle tannins, stronger tannins, bigger tannins, but more elegant tannins as a result of that. Additionally, there is more complexity of flavor as a result.

for the rest of the interview, try this link:

clyde

Hi Clyde, Tom,

But isn't Mondavi referring to oak tannins in his quote--the temperature is a good thing because it leads to increased extraction of oak tannins? Because if that's what he's saying, it seems like Tom is maybe right. If it's old neutral oak, the tannins are gone, and it's not clear that any temperature difference would be enough to make any difference.

Or did I misunderstand Mondavi?

Dave

I don't think he was referring to oak tannins. It sounded like he meant tannins from the fruit itself.

Because if that's what he's saying, it seems like

I think you overlooked the fact that he's not _barrel_ fermenting in oak; he's fermenting in oak _tanks_ - probably in the 1000-2000 gallon range. That's a different kettle of fish - so to speak. I don't know of any commercial winery that barrel ferments reds.

Tom S

I can recall a picture, either online or in WBM, of some central coast pinot noir vintner that had the heads off a whole slew of 59 gallon barrels and was going down the line punching them down. Looked like a royal PIA. Got enough of those going already!!

I agree with Tom and think Tim was eluding to "sculpting" the grape tannins with heat retention from the oak's insulating qualities. Their tanks are indeed sizable, to the tune of 5k gallons (see WBM article "To Kalon"). You can bet they use these for a few years before 'discarding', which means oak tannins is not a concern/factor.

clyde

From my reading he was saying that because oak retains heat better than stainless, it will extract more grape tannins (higher temperature = greater tannin extraction). He explicitly mentions that the oak doesn't directly contribute flavors. I just re-read it and it seems like standard winemaking gobbledegook - it works but he doesn't know why. If it were just temperature, then Mondavi could heat up their tanks to maintain the same temperature.

Well, we have a half-dozen 2000 oak barrels that we've just taken the tops off of. I'm in the middle of a test where I've filled the barrel

Note that there was wine in the barrel until a month ago. It was sulphered and handled well. BUT... I went down this evening and noticed that four days after we took the top of the barrel, there is mold growing above the water line on the still moist from wine inside of the barrel. So I'm a bit concerned about the sanitization issue you raised.

...Michael

I've considered doing that myself, but I seriously doubt that it would be worth the effort - even for a ton or so of fruit.

Maybe someday - when I have nothing better to do...

Tom S

The problem is, you filled the barrel with _water_, at pH 7 or so, and _warmed_ it in the presence of air. That's an ideal climate for molds and fungi to grow in.

If you'd acidified the water to pH 3 or so and sulfited it to 20-30 ppm free SO2 you wouldn't have any mold growing in those barrels - at least not until the free SO2 dropped to near zero.

Now, those barrels need an ozone treatment or steam cleaning to kill the stuff that's growing in them before you can safely put wine into them again.

Tom S

Yeah, but I had assumed we were talking about Chardonnay (that is where we started, right?), and if so, there's no where to extract grape tannins from.

Thus my comment that it had to be oak tannins.

Dave

I've never had any luck getting water, even heavily sulfited water, to not mold if left in barrels longer than it takes to swell the barrel (a day or so).

I don't know why. But anyway, I never leave water in barrels that I care about.

Dave

IIRC, the original post was concerning _red_ grapes. I'm not sure if the varietal was mentioned.

Tom S

You only have a couple of options:

(1) Water with sulfite and citric acid (to keep the pH down and the SO2 in the molecular form), or

(2) Rinse the barrel thoroughly, gas it with SO2 (either from a cylinder or a burning sulfur wick), bung it tight and let it dry out. You may need to tighten the hoops and soak the barrel until it stops leaking again if you leave it dry for more than a month or two, but this method is the best for long term storage without losing oak flavor. Most of the commercial wineries store empties dry.

Tom S

I let them sit dry, burning a sulfur wick every 6-8 weeks, and then swelling them when I need them.

That's worked pretty consistently.

Dave

Ah. Sorry, my mistake. I guess I just assumed chard, since we were talking about fermenting in barrels.

Nevermind.

Dave