I started a test today. I prepared a mix from 2 cups heavy cream, 1 cup water, 16 g whey protein, 6 egg yolks, 1/4 cup erythritol, and a pinch salt. I added stevia to taste (and lost track of how much I added). I cooked the mix (a little too much---oops), strained it. I divided it in half. To one half added 2g of cremodan 30 and to the other half I added a tablespoon of glycerin. Then I chilled the mixes in an ice bath and churned them. The first batch I churned was the cremodan mix. It chilled (much) faster (because it was in a metal bowl) and when it reached 40 deg F I churned it until it was too thick to move in the machine, about 3 minutes. I attempted to measure the overrun and estimated it at about 5% (the weight of a cup of the mix went from 8.2 oz to 7.8 oz). I chilled the second batch (with the glycerin) and it actually ended up a bit colder, about 37 F before I churned it. I'm using the Cuisinart with the bowls you chill in the freezer and I have two bowls that were both well chilled in my chest freezer, so I started with a fresh bowl each time. The batch with the glycerin had a much longer residence time in the machine, about 6 minutes. It was clearly softer at the point where it was no longer moving in the machine. I measured the overrun at 18% (the weight of a cup went from 8 oz to 6.8 oz). I do wonder what the effect of batch size is on overrun. I'm also not sure why the mix with the glycerin was 0.2 oz lighter before churning. One possible explanation is that because the mix containing cremodan was thicker, I filled the measuring cup above its sides slightly and had more mix in it. If that's the case then 5% was an overestimate on the overrun.
The remaining ice cream is chilling in the freezer and I'll assess scoopability tomorrow.
