Why Dried Shiitake Changes a Broth

A broth made with fresh shiitake and one made with rehydrated dried shiitake can seem to involve two different mushrooms. The dried version runs far deeper, and only the dried version leaves soaking water too good to pour out. The gap is chemistry that happens during drying, and the molecule at the center has a name.

The molecule is guanylate

Guanylate, another umami nucleotide, is especially high in dried mushrooms such as shiitake.¹

The qualifier dried is the condition. Guanylate's home ground is the dried mushroom specifically, which promotes drying from a preservation method to a process that changes composition.

Drying mushrooms concentrates and increases their guanylate content, deepening umami.²

Concentrates and increases, side by side, is worth a pause. Water leaves and relative concentration climbs, and on top of that the content itself grows. This is why piling in fresh shiitake never quite does the work of a single dried cap.

A heavier weight class

In a published review of the umami receptor, guanosine monophosphate is described as more potent than inosinate while adenosine monophosphate and xanthosine monophosphate have weaker effects, and a separate study gives relative umami potency against monosodium glutamate as 0.18 for adenylate, 1.0 for inosinate and 2.3 for guanylate, with taste thresholds of 12.5 milligrams per 100 grams for guanylate and 50 for adenylate. Guanylate carrying more than twice the weight of inosinate is the quantitative argument for putting a dried mushroom into a stock built on dried fish.³

A molecule more than twice as potent per unit weight as the inosinate supplied by bonito flakes and anchovies happens to concentrate in dried shiitake. The habit of slipping one shiitake into an anchovy stock is a kitchen discovering that ranking ahead of the literature.

How you dry it is a fork in the road

Measurements exist showing that the drying method splits the outcome, with aroma and umami each favoring a different route.

In a study that dried fresh Lentinula edodes shiitake by hot air drying, freeze drying, and natural drying, hot air dried mushrooms carried by far the highest level of cyclic sulfur compounds, 56.55 micrograms per gram against 7.24 for fresh, 3.90 for freeze dried, and 0.04 for natural dried, and showed the strongest typical shiitake aroma, while freeze dried mushrooms held the lowest total free amino acids at 29.13 milligrams per gram yet the highest umami taste amino acids at 3.97 milligrams per gram and the highest equivalent umami concentration at 29.88 grams of monosodium glutamate per 100 grams. That study frames the choice as method bound: hot air drying for aroma, freeze drying for umami.⁴

Dried shiitake at the market commonly comes from the hot-air or natural-drying routes, so the intense shiitake aroma we know is largely that family's product. The takeaway from the measurement is that the best drying method depends on whether aroma or the umami number sits at the top of your list.

What a finer panel adds

In a study of shiitake drying, the 5 prime nucleotide pool rose after drying, led by 5 prime CMP at 3.14 to 8.36 milligrams per gram and 5 prime AMP at 2.60 to 4.92 milligrams per gram as the two main nucleotides measured, and among the three nucleotides usually tracked for umami flavor, that study detected only 5 prime GMP: 5 prime IMP and 5 prime XMP did not appear in its samples.⁵

Of the three umami nucleotides usually tracked, the only one that showed up in shiitake was GMP, the guanylate. That squares with the picture so far, and it also means the inosinate axis still has to come from somewhere else, which is what the anchovies and bonito are for.

• To deepen a broth, test one or two dried shiitake caps before reaching for more fresh mushrooms.
• Always pour the shiitake soaking water into the pot. It is the guanylate, extracted.
• Add dried shiitake to an anchovy or bonito stock and taste the layering as the guanylate axis joins the inosinate axis.
• Separate the dishes where shiitake aroma leads from the ones that just need the umami number. The same dried cap gets used in different amounts and soaking times depending on which it is.