Which property of hops improves with the addition of tetrahydro-iso-alpha acids?

The property of hops that improves with the addition of tetrahydro-iso-alpha acids is foam stability. Tetrahydro-iso-alpha acids are the products of the hydrogenation of iso-alpha acids, which are formed during the boiling of hops in the brewing process. These compounds have been shown to enhance the stability and retention of beer foam.

Foam stability is critical in beer as it affects the overall enjoyment and sensory experience. A good foam head can improve the beer's appearance and can influence the perception of aroma and flavor. The presence of tetrahydro-iso-alpha acids contributes to the formation of stable foam by improving the surface tension properties of the beer and aiding in the formation of bubbles.

Enhancing foam stability through these acids is particularly important in certain beer styles where a robust and creamy head is desired. While other options may relate to characteristics of hops and beer, the specific improvement associated with tetrahydro-iso-alpha acids is most directly related to foam stability.