Bulk priming a different approach

I currently have 20L of a Hazy IPA cold crashing in a fermzilla which I need to bottle. I intend to batch prime by dissolving sugar in a small amount of boiling water and after cooling add to a second Fermzilla purge with CO2 and then close transfer the beer on top trying to avoid any oxygen pick up. I will then bottle as usual with a duo tight bottle filler. However I am unsure how much priming sugar to use as I am aware that the calculations are temperature based and whilst it was fermented at 19°c it is now down to 2°c and I also added CO2 to the fermenter before cold crashing to prevent the fermzilla collapsing.

Brewers friend calculator suggests that there is double the amount of dissolved CO2 in a beer at 19° and that at 2°c. I understand that there are many variables but would like to canvass other people opinions before I carry on

I think the temp/carbonation 'equation' is based on the fermentation temp, and that the secondary fermentation temp should be same as initial fermentation - so I would work it out at 19

The calculator notes include this:

However, if the beer was cold crashed, or put through a diacetyl rest, or the temperature changed for some other reason... you will need to use your judgment to decide which temperature is most representative. During cold crashing, some of the CO2 in the head space will go back into the beer. If you cold crashed for a very long time this may represent a significant increase in dissolved CO2. There is a lot of online debate about this and the internet is thin on concrete answers backed by research. We are open to improving the calculator so please let us know of any sources that clarify this point.

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Larse said:

The calculator notes include this:

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Yep that is as my concern

Did you ferment under pressure? I guess not . I think the amount of co2 ingested by the beer on cold crash will be minimal really . I would proceed as if there is none. I bottle the majority of my brews and juts take the figure from brewfather (same process as you. Dissolve etc) irrespective of any cold crash..

Brewfather gives me...

That’s very helpful thank you

Just a question if I may, sorry I can’t answer yours. If you have a couple of pressure fermenters why not carbonate in the second fermenter and then bottle the carbonated beer using a counter pressure bottle filler?

Buffers brewery said:

Just a question if I may, sorry I can’t answer yours. If you have a couple of pressure fermenters why not carbonate in the second fermenter and then bottle the carbonated beer using a counter pressure bottle filler?

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Very valid point but I’m not confident in bottling carbonated beer and this is for my son in law. Plus I want to free up the fermentation fridge so I can get another brew for myself.

I also ferment at 19C, cold crash close to zero for a couple of days and then batch prime with sucrose. I did some fairly accurate measurements on CO2 absorption and for my fermenter I get about 3L of CO2 pulled back into the fermenter during the 2-day cold crash time. Some of this will be contraction of headspace and some absorbed by the beer. There is about 7L of headspace and 26L of beer in my fermenter.

I am not going to do all the boring maths here but it worked out that for my fermenter geometry, the beer had absorbed approximately 2.5L of CO2 equivalent to another 0.1 vols (roughly). Basically hardly worth bothering about, for me anyway. Alternatively I could have adjusted this by using 16C in the priming calculator instead of 19C as that equates to about 0.1 vols difference.

Steveski said:

I also ferment at 19C, cold crash close to zero for a couple of days and then batch prime with sucrose. I did some fairly accurate measurements on CO2 absorption and for my fermenter I get about 3L of CO2 pulled back into the fermenter during the 2-day cold crash time. Some of this will be contraction of headspace and some absorbed by the beer. There is about 7L of headspace and 26L of beer in my fermenter.

I am not going to do all the boring maths here but it worked out that for my fermenter geometry, the beer had absorbed approximately 2.5L of CO2 equivalent to another 0.1 vols (roughly). Basically hardly worth bothering about, for me anyway. Alternatively I could have adjusted this by using 16C in the priming calculator instead of 19C as that equates to about 0.1 vols difference.

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Fantastic that’s just what I needed

Steveski said:

I also ferment at 19C, cold crash close to zero for a couple of days and then batch prime with sucrose. I did some fairly accurate measurements on CO2 absorption and for my fermenter I get about 3L of CO2 pulled back into the fermenter during the 2-day cold crash time. Some of this will be contraction of headspace and some absorbed by the beer. There is about 7L of headspace and 26L of beer in my fermenter.

I am not going to do all the boring maths here but it worked out that for my fermenter geometry, the beer had absorbed approximately 2.5L of CO2 equivalent to another 0.1 vols (roughly). Basically hardly worth bothering about, for me anyway. Alternatively I could have adjusted this by using 16C in the priming calculator instead of 19C as that equates to about 0.1 vols difference.

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Well done for doing the hard math and coming to the same conclusion I did , based on common sense (no offence intended)