Advice needed regarding a slow fermentation

[Terry Chalk]

I need a bit of advice about a slow fermentation. Sorry this tale is so long but I have included all the information that I have. I have been making “hobby” cider with some success for about 8 years.

This year because of a “killer” frost that trashed my fruit just as it was forming. I have had to use juice from a commercial orchard that wasn’t affected by the frost. I have used their preservative free juice previously without any issues. The juices are single variety, some of which I have previously blended together to make a nice “quaffer”.

The current fermentation is much slower than usual. After 70 days (10 weeks), it is only at SG 1.010 and 12 FSU, with no noticeable change over the past week. I am concerned it may never reach close to 1.000. A few bubbles are still rising in the carboys, and the airlocks occasionally bloop, but at less than one bloop per minute.

I have used the same source of juice before in similar circumstances and it has taken between three and five weeks to fully ferment. This is the norm for juice from my own trees. Just to add to the confusion, a batch of “new” juice from a friend’s tree (also from a nearby area that wasn’t affected by the frost) is down to 1.000 after only three weeks.

The “problem” batches are quite normal (OG 1.050, pH 3.8, TA 5.5g/L, S02 5% solution to start at 50ppm) fermented with S04 (usually reliable and well behaved) and supplemented with Fermaid at SG 1.026. Because of the slow fermentation, the “new” batch is on M02 just in case there is some problem with the S04 which was from a new pack, in date, etc.

So, my dilemma is do I add some M02 to see if things kick along or just wait and see. I have a couple of M02 starters developing as I write.

The only difference between this and other years is temperature. We are suffering very cold mornings below freezing (Snowy Mountains, Australia), so I have brought all batches inside to a 10C-18C environment. This is below the ideal range for S04 but O.K. for the M02.

My initial fermentation is usually completed by the end of Autumn (May) when it is a bit warmer. Is the slow fermentation typical of cold climate winter behaviour or do I have a problem with the S04?

Any advice regarding what might be happening is gratefully appreciated. 

[Bartek Knapek]

If my calculations are correct, 12 FSU means the gravity is dropping ~0.8g/L per week - such a rate is quite normal for low temperatures and low initial YAN conditions. If the apples come from a low/non-fertilized orchard, they are likely to be quite low in YAN. Your friend may have different soil or use some fertilizer. The apples may also have a different natural microflora. All this makes a difference. 

How did the fermentation rate behave over time?
Have you observed any difference after supplementing with Fermaid?
Is it slowing down, or steady at 12 FSU? 

I suppose you are not interested in preserving any natural sweetness, but rather want a shelf-stable product?

Have you considered warming up the carboys for a couple of days to see the difference, or is that not possible or too costly?

//Bartek

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[Claude Jolicoeur]

Le jeudi 23 juillet 2026 à 21:24:20 UTC-4, Terry Chalk a écrit :

The current fermentation is much slower than usual. After 70 days (10 weeks), it is only at SG 1.010 and 12 FSU, with no noticeable change over the past week. I am concerned it may never reach close to 1.000. A few bubbles are still rising in the carboys, and the airlocks occasionally bloop, but at less than one bloop per minute.

You could take this opportunity for making an off-dry sparkling cider.

By bottling it now as-is in bottles that can take some pressure (e.g. beer of champenoise), the cider would ferment a few more points of SG in the bottles and finish probably around 1.007, thus yielding a cider with about 15 g/L of residual sugar.

Who konws, you might like it!

 

[Terry Chalk]

Thank you for the replies Bartek and Claude. Your comments have given me something to think about.

I have considered bottling now for a potentially off-dry cider but was concerned that at SG1.010 it may continue to ferment to the point where I have 4 volumes or more of C02 (a bit fizzy). Normally I would completely ferment then add the right amount of sugar for 2.5 volumes of C02 plus some for residual sweetness (i.e. bottle and monitor bottle pressure to assess sugar converted to C02 and how much is left for sweetness, then pasteurise).

I have had an occasion in the past when fermentation stalled around 1.010 but started up again after DAP was added. This is why the Fermaid was added at 1.026 “just in case”. However, it didn’t seem to make any difference to the fermentation rate which was more-or-less normal (i.e. started quite fast then slowed down), except for a bit of a burst in the airlock for a couple of hours. I do suspect that the juice is from well fertilised trees as the orchard’s main commercial business is juice rather than fruit (they also make their own cider).

Because I added Fermaid at 1.026 as “insurance” against stalling, I have been a little reluctant to add DAP at this stage but maybe 0.25g in one batch is worth a try. Similarly letting another batch sit in a warmer environment at least might tell me if I have a nutrient or low temperature issue.