This is similar to this question, but a very different base so I'm asking this separately. I make ice cream fairly often, I have a very reliable base I add flavorings to, like mint extract, chocolate, nutella, strawberries, etc and I always get a nice, scoopable result after hardening in the freezer.
The base is:
- 650ml whole milk
- 225ml double cream (UK cream with 50% fat content)
- 170g sugar
- 5 egg yolks
- 1/2 tsp vanilla
- 1/4 tsp guar gum
- 1/2 tsp salt
I make the base by heating the milk and 2/3 of the sugar until steamy, whipping the yolks with the rest of the sugar, then drizzling the hot milk into the egg-sugar mix so it doesn't cook before heating it all up to make the custard. I then add flavorings, for example 200g of nutella, and the guar gum, leaving the salt out if I'm adding anything which is salty already like Nutella or peanut butter. I use a stick blender to mix it all thoroughly.
After chilling in the refrigerator I churn it in a kitchen aid attachment which is a frozen bowl with a dasher, usually about 16-18 minutes, adding any drizzles or chunky ingredients in the last minute. Then I scoop it all out into a plastic container and freeze it to harden up.
I've used this recipe and method many times and I've never had a hard ice cream yet, this time I decided to do peanut butter cup ice cream. I did my usual base and blended 200g of salted smooth 40% fat peanut butter into it. Towards the end of churning the kitchen aid started to struggle as the mix got very thick, much thicker than usual. After hardening up in the freezer I had to practically chisel the stuff out into bowls, and even after warming up again it's still not pliable like ice cream should be.
What's causing my ice cream to be so hard, and what can I do to fix it? I thought it may not have enough fat, but the peanut butter is nearly 50% fat so that doesn't make sense. I added more sugar than usual to offset the unsweetened peanut butter, and 5 egg yolks should be plenty. Should I be adding more stabilizers or different types of additives? I churned it for the same amount of time as I always do, but it only seemed to get really hard towards the end, should I churn it less?