Hello Paul,
Last year we did Merlot and Cabernet Sauvignon. We picked up one batch about a week after the other so their primary fermentations were a bit staggered. Anyway, to answer your question, the Merlot grapes remained in the primary for 4 weeks and it was reading 0.996 Brix 6 days before pressing. Remember there will be a blanket of CO2 emitted from fermentation and so long as you don't mix it up too and allow ambient air to become exposed to the must, you should be fine.
Once primary was done, there was less of a defined cap on the must. I still wanted to punch down to get the skins in contact with more of the must but when I did, I did so very slowly in an attempt to keep the CO2 atmosphere above the must as undisturbed as possible. One aspect of our setup that was beneficial was the amount of head space in the primary. I would estimate there was 12-18 inches of wall from the top of the must to the top of the fermenter; this allowed a large amount of CO2 to accumulate. One gentleman did recommend the option of using food grade argon but I decided not to go that route.
-Jenks
I am trying to understand what you did.
Wine was completely dry 6 days before you pressed, so basically, you did a 6 day extended maceration. Right? In other words, for all but the last 6 days, the wine was still fermenting. Still right?
So if the wine was in primary for 4 weeks, that means it took about 3 weeks to ferment to dry, if I am understanding you. That is a pretty long period of time to go dry. What yeast were you using and what was the temperature of the must during most of that 3 weeks?
Right now I am doing a rose from fresh Zin grapes with D47 yeast at a maximum temperature of about 70F, which is a little higher than I want. Even at that, the SG is dropping like crazy. 70F is as low as I can realistically keep the temperature or fermentation would go a little slower.
Like you said, if you kept the container closed and didn't overly agitate the must, there would still be a good amount of CO2 left even after 6 days of maceration. Wine with all the skins after fermentation would be saturated with CO2, even when pushing down the cap. The key is keeping the container closed whenever possible.
That's where a little dry ice can help. You can put small pieces on top of the must; it won't change the temperature of the must by much; but it will produce nice amounts of CO2 for protection.
In Paul's case, I would not recommend him to try an extended maceration his first time. He needs to get through a complete cycle before he tries something like that. Especially since he doesn't really know the tannic structure of the grapes. It will give him something new to try next time.
