A dressing of oil and vinegar alone is doomed to make a wilted, unsatisfying salad. As the two struggle to bond, you can be left with a dressing where the oil will cling to the leaves and the vinegar will get friendly with the bottom of the bowl. This is because salad leaves have a protective oily cuticle layer that reacts differently to different substances.
With vinegar (or other water-based liquids), the leaves prevent absorption and keep crisp. A protective mechanism for when it’s raining in the wild. However, with the oil, salad leaves begin to absorb the similar oily consistency and their shape and color diminish.
Using a dressing from just vinegar is out of the question, as it would make an extremely sharp-tasting salad. The answer is using an emulsifier. Emulsifiers like honey, mayonnaise, tomato paste, or even smashed avocado bring the elements of oil and vinegar together. The emulsion allows the oil to remain suspended with the vinegar on the exterior of the leaf — no absorption means crispy salad leaves for longer and you have a guaranteed balance of flavors too.
