Natural fermentation - stuck?

Hi. My dad and I have been making red and white wine for some years (concord and niagara grapes), and we use a straightforward, natural fermentation process. We have never added any yeast, and the wine almost always turns out pretty nice. This year, however, I’ve got a stuck fermentation. The initial sugar level of the must seemed a bit low (6.2 brix for the red and 4.0 brix for the white), but I added sugar to bring the red to 23 and the white to 21.5. It went into the carboys on 11/10, and today, the red is only at 22.4 (started at 23) and the white is better at 18 (started at 21.5).

We’ve let the fermentation go in the past until about February, but I decided to check it today, and it seemed stuck. Is it that the natural fermentation process does just take that much longer, or might I have a stuck fermentation? If so, can I kick start it by adding yeast? If not, how might i get it going again? The juice tastes great, although a little sweet for my taste. Any thoughts? Thanks.



The good news is, if the juice still tastes good, you’re in good shape. The starting Brix isn’t too high, so you’ve got that going for you.

After this much time it must be a stuck fermentation. I’d recommend adding a commercial yeast in a starter to get it going. You could use a liquid yeast and the procedure outlined here, but you could do just as well with a packet of Champagne yeast (I’d recommend Lalvin EC1118). First, make sure your juice is above 65F–you need to give the yeast a running start.

Next, for each batch, get a container of natural apple juice without any preservatives (sorbate, sulphite, benzoate, etc), sanitise a small bottle (a pint milk bottle will do, or a wine bottle, anything you can cover with cling wrap to keep dust and bugs out), fill it halfway with juice (minimum of two cups), warm it to 100F (no warmer!) and add the yeast. Cover it with cling wrap (or an airlock, or a cotton ball–you just want to keep it clean) and leave it for a couple of days.

When it’s foamed up, and then mostly subsided (2-3 days), cool the starter to exactly the temperature of the juice. This is crucial. If you don’t do it, you’ll introduce temperature sheer and the yeast will die. Shake the container and add all of the juice/yeast blend to the batch.

Keep the wine at 65F or so until it shows vigorous fermentation. Don’t let it get much colder than 55F or it may stall out again. Check the sg once a week to make sure you’re seeing progress. That should do it.

Hi Tim. Happy New Year! And thanks for replying. You mentioned temperature and it hit me that I didn’t consider this and had the wine in my basement, which keeps at about 60 degrees. Is it possible it was just too cool down there and the fermentation was just slow? I’ve brought the carboys upstairs where we keep the house about 68-70 degrees. I think I’ll wait a couple weeks to see if any activity starts and check the gravity a couple times during that time to see if it drops before trying yeast. If I do go the yeast route, you mention using natural apple juice. Is there a reason I shouldn’t use the grape juice I have? Also, regarding the starting brix, I shot for those levels because I had read that’s about the level I would want for a medium sweet wine. The juice is currently still quite sweet, but I figured that’s because it isn’t done fermenting. Do you have any thoughts on that? Again, thank you for taking the time to respond!

Oh, it looks like we’ve put our finger on your issue!

At this point, I would definitely add yeast. First, there’s no way it can hurt the wine, and second, it will help keep any potential spoilage organisms that might have gotten a foothold in the wine while it was cold, in check. I always use apple juice because it’s easy to get without a lot of added sugar or preservatives–grape juice is harder to find without those.

Keep a close eye on the specific gravity as it warms up, but you’re probably going to be okay.


Hi Tim. Thanks again for getting back to me. My daughter has been in town since right before the new year, so I haven’t had much opportunity to play with this. I can see, though, that the juice is active again after bringing it upstairs and it’s had a chance to warm up a bit. As you suggested, though, I am still considering adding the yeast. As for the juice to use, I was asking if there’s a reason I shouldn’t remove some of the fermenting juice from the carboy and use that as a starter, as opposed to adding apple juice? Thanks Tim!

You could try the juice as as starter, but check the specific gravity first: if it’s dropped by more than half, do a starter from apple juice, because you want to get the yeast off to a good start without competing with a wild strain.

Good luck!

Hi Tim. I just wanted to pass on an update, as I figured it might help someone else too. I got some straight apple juice, no preservatives, and added the yeast and let it set for about 36 hours and added it to the wine. Nothing happened. So I decided to try doing a starter like I do with my beer. I took a couple more cups of juice and added about half a cup of corn sugar (table sugar would probably do also, but I’ve got the refined sugar for my brewing/bottling, so I used that). I boiled the juice for 5 minutes, then put the pan in an ice batch and cooled it to about 90 degrees F. I put that juice in my flask and put it on my stir plate and pitched the yeast. I let it set on the stir plate for a day. The starter was definitely going well this time. I then poured the whole thing into one of my carboys. Within a day, it was clearly evident the juice was again fermenting. I’ve done the same thing to my other carboys, and all are again active and on the way to some tasty wine. Thank you for taking the time to get me on the right track to fixing this situation. Much appreciated!

Awesome! That’s great news. I’m glad you could get it going again. Keep us updated on how it turns out.

Hi. I’ve got a follow-up to this ‘stuck’ fermentation post from February. Both the red (concord) and white (niagara) did indeed restart fermentation after adding the apple juice starter, but they both stopped again at a reading of 13 brix on my refractometer. It’s making me wonder about how I’m doing my conversion, and if it’s the same for wine as it is for beer. I use the Norther Brewer refractometer conversion site for both. My starting gravity for the red was 23 bx and 22 for the white. Per the converter, with an ending gravity of 13, it ends up at 8.9% ABV for the red and 7% for the white. Is that right, and is that normal? I must say, though, the flavor for both came out quite exceptional. :smile: Thanks.

I found a slightly different formula at the site Wine Alcohol Content Calculator – Winemaker's Academy. Here, the formula is %ABV = [(OG-FG)/7.36] x 1000 which puts my red at 9.8% and white at 8.8%. But, that’s using the NB refractometer calculator to convert brix to SG, so would there still be some differences?