So I did a 100g brew from the same batch I had done an earlier 50g brew. The 50g brew was good, but the 100g brew didn't provide anything but a fuzzy head.

I brewed slowly with 9 litres of water and vinegar added. I did notice that the 50g brew seemed more redish in colour yet the 100g brew was more yellow. Not sure ifnthis has much to do with its potency. But I was a bit surprised at the results, I know it's a bit brief but if someone has any input as to what happened from experience I'd appreciate it.

The obvious question would be: What variables changed from one brew to the other?

Were both from same batch? Was vine powdered or shredded? How was one brewed in comparison to the other (you only described one, and it seems you implied one boil only??)? Had you consumed any other substances the same day or day before? Was the setting different? Was your diet different?

Brew of what?

Shredded yellow Caapi.

I did a longer brew than the 3 x 3, it was Caapi only. Diet was similar and consisted of salad the day before and the day of, I suppose I used slightly less vinegar as many said it doesn't do anything, I was on the fence about that so I slowly reduced vinegar amounts later in the brew. Example: First 1.5l boil was 1.5 table spoon Vinegar, same on second, third was 1 tablespoon vinrgar, fourth was half a table spoon and the remainder stayed at .5 tablespoon vinegar. I boiled using 1.5l bottled water. The Caapi batch was from the same bag, I even squeezed the last drops grom the first batch I had used and put it intonthis brew.

The only change was I did freeze at one stage because I hasn't sure I was going to be able to complete it, and that I drank it cold as opposed to warm/hot.