Cold crashing and effects on natural carbonation

[Clouds]

Greetings fellow brewers, I have a question that is hounding me a bit and would love some clarification, please excuse my naivety if the answer is obvious..
I have been making beer for a while and naturally carbonate my beer with priming sugar(dextrose) using this chart http://www.brewblogger.net/?page=tools&section=sugar&action=calculate
Recently I acquired a fridge that I can fit my fermentor into and have begun cold crashing my beer prior to bottling to try get a clearer beer.. Now the above chart works on temps that the beer is bottled at, does that mean I should follow that chart even though the fermentation was at a higher temp and I only cold crashed when I got to expected F.G ? There is a radical difference in priming sugar due to temps and I am worried I will be under carbonated if I follow the temp chart or over carbonated if I use the average fermentation temperature.

To give an example I made a Belgium Blonde all grain beer
The O.G was 1.052 and I kept the fermentation temperature at 18C or 65F for its entire fermentation period ( 2 weeks ) reaching my target F.G of 1.010.
When I reached 1.010 I then dropped most off the trub out - I have a conical fermentor - and then I turned on the fridge and dropped the temp of the beer to 2C or 35F over two days
Then I went to bottling , I used the priming calculator chart and calculated the dextrose needed based on the 65F fermentation and 2.2volumes of saturation and my 50L or 13.2 gallons amount of beer and got a result of 299grams of dextrose needed.
If I use the chart but base the sugar needed on the current temp of the beer 2c or 35F directly after cold crashing then I get 161grams - almost half

I really want to try get this right and hope someone can help

 

[IslandLizard]

Most calculations to determine residual carbonation left in beer, go by the highest temp the beer has been at since fermentation finished. That's the maximum amount of CO2 that can still be dissolved at any time, although it could be less.* Say you fermented at 68F, but conditioned at 72-74F for a few days, then 74F is your highest temp, and her associated dissolved CO2 level. Cold crashing is lowering temps, and has no effect.

* Now, if you (partially) degas the beer at some point, say by adding dry hops, stir, rouse yeast, etc., that changes things, and it becomes more of toss up, so use some judgment.

 

[Clouds]

Most calculations to determine residual carbonation left in beer, go by the highest temp the beer has been at since fermentation finished. That's the maximum amount of CO2 that can still be dissolved at any time, although it could be less.* Say you fermented at 68F, but conditioned at 72-74F for a few days, then 74F is your highest temp, and her associated dissolved CO2 level. Cold crashing is lowering temps, and has no effect.

* Now, if you (partially) degas the beer at some point, say by adding dry hops, stir, rouse yeast, etc., that changes things, and it becomes more of toss up, so use some judgment.

Thank you , I think I am on the right track from your reply , I normally add 300g dextrose per 50L and get results , its quite interesting though, on an IPA I get less bubbles than a Belgium using the same sugar and bringing them both down to 1.010 -- must be hops or something to do with opening the tank and add the dry hops but that's another journey as you say.

 

[IslandLizard]

must be hops or something to do with opening the tank and add the dry hops

Not the opening of the fermentor but adding dry hops creates nucleation sites which makes (some) CO2 to come out of solution. How much CO2 is lost is almost impossible to measure.

Let your experience be your guide. If your IPAs always tend to be somewhat under-carbonated, add some extra priming sugar at bottling. Take an educated guess.

 

[Clouds]

Thanks again IslandLizard, still waiting on my blonde to finish fermenting , its stuck on 1:020 now for a week , we have been having very cold weather here, one of my problems in the past has been impatience, I would use a two week rule for my fermentation and sometimes the fermentation would not be complete and with the addition of extra sugar to prime it would result in very carbonated beer, slowly slowly makes for good beer, my next lesson is going rather the keg route and to force carbonate and counter pressure fill

 

[IslandLizard]

Thanks again IslandLizard, still waiting on my blonde to finish fermenting , its stuck on 1:020 now for a week , we have been having very cold weather here, one of my problems in the past has been impatience, I would use a two week rule for my fermentation and sometimes the fermentation would not be complete and with the addition of extra sugar to prime it would result in very carbonated beer, slowly slowly makes for good beer, my next lesson is going rather the keg route and to force carbonate and counter pressure fill

A temp drop can coax a yeast to go into dormancy. Lack of Oxygen when pitching can be another, I later learned. I've had that happen and patience not only becomes a virtue, it's a test of endurance to sit it out. One 1.090 old ale (using 2 rehydrated packs of S-04) got stuck at 1.031. I'm quite sure temps didn't drop, they were in a large water jacket (cooler), but who knows? I carefully roused, with no effect. I ended up putting them in kegs, yeast cake all, and bubbled CO2 through once or twice a day, to more safely rouse them without risking oxidation. After 2 weeks, still no change! They were for our club's barrel project so it all evened out when mixed in with 10 other kegs. Some of those were as low as 1.014, but most in the 1.018 range.

Sometimes raising the temps slowly towards the end of fermentation helps prevent stalling.

I don't bottle much anymore, since I started kegging. So much easier. But it comes also with quite a lot more equipment.

Bottling from a keg takes some practice. I often end up with a somewhat under-carbonated beer in the bottles, even when filling under counter pressure.