However, usually I'll add a quick splash of ACV or rice wine vinegar, or if I'm feeling adventurous, my new bottle of ~ ume plum vinegar ~. (faring-well.com)
It was simple: apple + soaked cashews + ume plum vinegar (another acid and salt could work) + water. (tastespace.wordpress.com)
1/2 cup raw cashews, soaked in water for at least 1 hour, then rinsed and drained 1/4 apple, coarsely chopped 1 teaspoon ume plum vinegar (may sub with lemon juice or apple cider vinegar with a bit of salt perhaps) water to thin to desired consistency (I used around 1/2 cup but start with less since it will be more saucy initially. (tastespace.wordpress.com)