A Surprising Tahini Thickener

For our sesame-crusted salmon recipes (see related content), a smear of tahini on each fillet helps boost the sesame flavor. But tahini has a thin consistency, which means that it won’t stay put on the moist, slick surface of a fish fillet. To thicken the tahini and give it some holding power, the solution is a bit surprising: We stirred in 2 teaspoons of juice.

You’d think that adding a liquid would thin tahini rather than thicken it. Why the opposite? Tahini is simply sesame-seed butter, made by grinding hulled sesame seeds into a paste. Much of its makeup is carbohydrates, and when a small amount of juice (or any water-containing liquid) is added to tahini, a portion of each carbohydrate molecule is drawn to the water. As a result, clumps of carbohydrates appear. As the amount of water is increased, more clumps develop, causing the tahini to thicken overall. If you keep adding water, eventually you’ll cross over the threshold of thickening it; enough water in the system will cause the tahini to loosen and thin out. This is similar to what happens when chocolate seizes. A small amount of added water acts like a glue, wetting particles just enough to get them to stick together, but eventually if you add too much water, the mixture turns into an evenly thinned-out liquid.

This same process also occurs with peanut butter (both all-natural and commercial varieties of the stuff): For example, if you make satay sauce for grilled meat, peanut dipping sauce for spring rolls, or dan dan noodles, you will notice that clumps appear when you first add liquid to the peanut butter. But as you keep adding liquid to reach the required consistency for these sauces, the lumps disappear.