Calculating the dissolved CO2 in cider before bottle conditioning

So I have 25 gallons of hard cider that I am about to bottle. I'm having trouble estimating the residual CO2 in solution for two reasons:

1. After fermenting for three weeks at 66F, then I crashed the cider for three more weeks at 33F. Usually when I prime it's easy to use the fermentation temperature to calculate the residual CO2, but since I kept it cold I am wondering if some secondary fermentation might have allowed more CO2 to dissolve in the cooler cider? And if so, how much?
2. I am conducting some yeast tests and used 13 different yeasts including wine, ale, lager, and wild yeast. Some of the batches had visible carbonation in the samples I took, and some were totally flat. Thus, I know some batches have more dissolved CO2 than others.

While I could just avoid all the problems and force carbonate (my usual protocol), I have a lot of the samples in 1 gallon batches. Using a 5 gallon keg to carbonate 1 gallons just doesn't make sense.

One thing that might solve my problem is a cheap way to test for CO2, which doesn't require a big sample size.

Another option is being conservative about my sugar and yeast additions for priming. Because kept it cold for so long I am going to krausen with some active yeast and add sugar.

Anyone have other input or ideas.

Thanks for the help.

well, without any advice I went ahead and bottle primed with some dextrose solution. Per gallon I added about .6 oz of dextrose solution with 1 oz of corn sugar per 100mL (yeah I know I'm mixing units, and yes I measured in weight of solution v.s. volume because I couldn't find a 100mL graduated cylinder). We'll see if they carbonate and or explode on me. For right now their in a warm closet, in boxes, inside garbage bags, inside bigger boxes.

Crap, sorry I didn't see the first post.

It should be fine.

You calculate it based on the highest temp it's been at since fermentation stopped. It will outgas co2 as the temp goes up. When you chill it, it isn't creating more co2, so the co2 doesn't increase.

seabass07 said:

You calculate it based on the highest temp it's been at since fermentation stopped. It will outgas co2 as the temp goes up. When you chill it, it isn't creating more co2, so the co2 doesn't increase.

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that was the assumption I was going on, but I had some many kinds of yeast that some were more temperature tolerant than others and could have kept fermenting as the temp dropped. I was also convused when I was taking samples that some were clearly more carbonated that others.