To condition or not?

[misterjoe]

Hello
I am making a batch of sour cherry cider. First time I have done this particular recipe. Basically like this:
5 Gallons cider fermented with Mangrove Jack's cider yeast M02, starting ABV 1.05, fermented low 60s for 20 days. Added 3.5 pints of homemade sour cherry "juice" (quotes because it was very thick) made from steaming and mashing the fruits. I stupidly neglected to take ABV pre and post juice addition. Tasted six weeks later and still had a pretty raw bitter taste. I don't know for sure with fruit, but I am a cheesemaker by trade and I know that many bitter tasting flavonoids are molecularly complex and take a long time to be broken down in fermentation so I let it sit for four more months. I want it bubbly so my intention was to bottle condition with honey because the honey, cherries and apples are all from my very small town. It tastes really nice now but retains a surprising amount of carbonation which I did not expect. It is very cloudy so I would like to clarify with bentonite before bottling. If I clarify and bottle, I assume I will loose a good amount of that existing carbonation, but I am getting no activity on the airlock so I wonder just how much more will happen in the bottle. I can't know if the sugar is all gone because I forgot to take the ABV before and after the juice addition. So I am a little afraid of getting bottle bombs if I in-bottle condition. I am leaning towards doing it but if someone has a keen insight I would appreciate it.
Thank you.

 

[Chalkyt]

This is a bit rough, but is the way that I would approach the problem.

If you measure the SG now, it should tell you how much "sugar" is left for fermentation and conversion into alcohol and CO2 (the SG will actually be the result of anything that affects the liquid's density, but typically will be 80%+ fermentable sugar). You might have to adjust this a bit for any substantial solids in your brew since you mentioned that the cherry was quite thick and had some mashed up bits so you could have have some SFDE (Sugar Free Dry Extract) which of course isn't fermentable into CO2.

Fermenting a change in SG of two gravity points (SG 0.002) will generate 1 volume of CO2 (typically around 15 psi), so your current SG will tell you potentially how much CO2 will be generated if it continues fermenting down to 1.000.

A typical carbonation level for cider is around 2.0 - 2.5 volumes of CO2 (roughly the carbonation of beer or soft drink) and results from fermenting four or five gravity points (i.e. a change in SG of 0.004 - 0.005) inside the bottle.

So, without a kegging setup, your three choices are (1) bottle and let the fermentation continue if your SG indicates that it is around 1.005 now (or add priming sugar if it is already lower than 1.005), (2) let the fermentation continue until it falls to 1.005, then bottle and let it continue fermenting down to 1.000, (3) let the fermentation continue to around 0.005 above where you would like the taste to be (very roughly, 0.005 tastes about the same as about 1/2 teaspoon in a cup of coffee), then bottle and let the fermentation continue for another 0.005, then stop fermentation (I use heat pasteurising to do this).

Of course the question is "how do you know when the SG has fallen another 0.005 inside the bottle and generated 2.5 volumes of CO2?" The answers are ... guess (based on the rate that it has been fermenting at), or measure it. Measure is a bit hard unless you have bottled some in a bottle with a pressure gauge, but the easy option is to bottle some in a plastic soft drink bottle and do the "squeeze test". i.e. when it is firm like a Coke bottle, that is near enough. (and... when it is firm, you can "taste test", yum!)

Heat pasteurising involves heating the bottles enough to kill the remaining yeast and stop any further fermentation. Have a look at Pappers post at the top of the forum, or Jim Rausch's post 16 April 2018 (use the search function at the top of the page for other heat pasteurising options). Generally putting your bottles in a waterbath held at 65C for ten minutes, then removing them will do the job.

As the bottles heat up, the CO2 will be driven out of the liquid (cider) into the airspace at the top of the bottle and increase the pressure, which is one of the causes of bottle bombs (the CO2 is absorbed back into the liquid as it all cools down again, thus returning the pressure to normal). Around 2.5 volumes of carbonation in a bottle at room temperature when heated to 65C will create up to 100psi of bottle pressure which is below the pressure standards for most bottles, however you don't know if a bottle has flaws or damage so safety precautions such as gloves, goggles etc are recommended, just in case a bottle fails.

Hope this helps.

 

[misterjoe]

This is a great response, thank you

 

[Chalkyt]

Happy to help. We have all been down this path.

It just occurred to me that if you are bottling in flip-tops you need to be aware that they can start leaking CO2 at pressures around 80psi which is about what you would reach with 2 volumes of CO2 at 60C. Anything more than this needs crown seals.

The "minimum" temperature for heat pasteurisation is about 60C and bottles would need to be held at this temperature for something like 20 minutes to achieve effective pasteurisation (conventional wisdom says that cider needs 50 pasteurisation units or PUs but more recent views are that 30 PUs are enough. For the technically inclined, it is easier to google Del Veccio's formula than to explain PUs here). That said, some 2020 work out of Washington State University suggests that only one minute at 60C will stop the yeast but might not be enough to kill any spoilage pathogens etc in the cider.

As far as bottle strength is concerned. Most glass bottle manufacturers work to batch testing of 1.2 Mpa (about 160psi) however the extreme spread over individual bottles in a batch can be as high a +/- 50%, hence the "rule of thumb" is to limit pressure in common 12oz/330ml beer bottles to not more than 100psi or 7 volumes of CO2, which is about the pressure in some champagne bottles.

 

[misterjoe]

Happy to help. We have all been down this path.

It just occurred to me that if you are bottling in flip-tops you need to be aware that they can start leaking CO2 at pressures around 80psi which is about what you would reach with 2 volumes of CO2 at 60C. Anything more than this needs crown seals.

The "minimum" temperature for heat pasteurisation is about 60C and bottles would need to be held at this temperature for something like 20 minutes to achieve effective pasteurisation (conventional wisdom says that cider needs 50 pasteurisation units or PUs but more recent views are that 30 PUs are enough. For the technically inclined, it is easier to google Del Veccio's formula than to explain PUs here). That said, some 2020 work out of Washington State University suggests that only one minute at 60C will stop the yeast but might not be enough to kill any spoilage pathogens etc in the cider.

As far as bottle strength is concerned. Most glass bottle manufacturers work to batch testing of 1.2 Mpa (about 160psi) however the extreme spread over individual bottles in a batch can be as high a +/- 50%, hence the "rule of thumb" is to limit pressure in common 12oz/330ml beer bottles to not more than 100psi or 7 volumes of CO2, which is about the pressure in some champagne bottles.

thanks this is good info. I am going to be bottling with corked 750ml bottles. I have not done the "pressure test" with a plastic soda bottle method before so I think I will try that so as to have another feather in my cap. Since there are several factors outside of accurate measurement I think I am just going to err on the safe side and stop fermentation a little earlier than I might otherwise.