Did you solve the pectin riddle or are you still racking your brain about that? Never mind, we have a winner! :)
With much joy, I officially announce that the pectin riddle has been solved by Patrizia, who beat everybody to the punch, with the following answer (translated by me):
”it doesn’t jell because it requires acidic foodstuff (citric or tartaric acid) and not basic foodstuff (cream of tartar) to mix together. Cream of tartar is a leavening agent.”
Congratulations! :) As promised, she will receive two bottles of maple syrup, straight from Canada. I also take the opportunity to thank all the other participants. If you liked the context, I will create others like this in the future.
But let’s see in more details, what went wrong in the preparation of my fruit pastes.
Patrizia has well understood that the problem was the use of cream of tartar, which I naively selected over tartaric acid. Tartaric acid has an acidity between pH 3 and 4, roughly. Cream of tartar is, instead, the potassium salt of tartaric acid, better known with the name of potassium bitartrate. Cream of tartar can easily protonate and, consequently, diminish the acidity of the reaction medium.
In my case, cream of tartar provoked an increment in the pH, with following deprotonation of the –COOH groups of pectin. The negatively charged carboxylic groups now repulse each other, preventing the association of pectin’s chain and the formation of the gel.
Thus, just to draw some conclusions here, make sure you have an acidic pH, better if between 3-4, when preparing jams of fruit pastes or jellies. How to get that?
1. Many recipes recommend to add lemon juice to your fruit blend. That helps achieving the right pH for jelling.
2. Alternatively, you can replace lemon juice with citric acid. I usually prefer this solution. Citric acid is easy to dose, is a standardized product, lasts long and is ready for use.
I moved the Thursday’s recipe to Friday, I hope you don’t mind. This is going to be the last recipe with pectin, at least for a while :)
Meanwhile, good luck with your fruit jellies!
Dawson et al., Data for Biochemical Research, 1959, Clarendon Press
Hervé This, Pentole e provette, 44-45, Gambero Rosso