yuzu peel
ingredient / ingredient-yuzu-peel
柚子の皮 / Citrus junos
Peel of yuzu (Citrus junos), consisting of the outer flavedo (yellow, containing essential oils) and inner albedo (white pith). The peel contains bitter constituents such as naringin, but no source was found that measured the flavedo and the white pith separately to show whether the pith holds more. When used as an ingredient, the peel is often prepared by boiling and discarding the water, scraping off the white pith, soaking in water, or adding sugar. Peel made into marmalade is treated separately as yuzu peel marmalade.
On this page (8 sections)
Reading the bitterness
Yuzu peel consists of an outer yellow layer (flavedo) and an inner white pith (albedo). A kitchen article, saying the white part is bitter, records a procedure of boiling for about 1 and a half to 2 minutes after the water returns to a boil, scraping off the white part with a spoon, and then soaking the peel in water for about 1 day while changing the water 2 or 3 times. However, no source was found that compared bitterness with and without removing the white pith. A study that examined the amount of naringin extracted for marmalade reported that home-made marmalade contained more naringin than commercial products, and states that this is thought to be because commercial products undergo bitterness-removal steps such as soaking in water. That study also measured naringin in the outer peel and in a material that includes the white pith, and does not give a value for the white pith alone.
An analysis of marmalade production that tracked the process of soaking yuzu peel in water and then heating it records that naringin decreased by 63 to 76 percent, while nomilin, another candidate bitter constituent, increased from 5.4 to 15.8 ppm. Because constituents that may be involved in bitterness move in opposite directions, it cannot be said that the peel's bitterness uniformly weakens. A review also includes a statement that heating itself has an aspect of generating bitterness, but this is a secondhand citation of another source that the review cites, not a directly confirmed finding.
Sources for this overview
Checked for this overview: The part introducing the difference in naringin amount between home-made and commercial products. / The part introducing the review's statement that heating generates bitterness.
Checked for this overview: The part introducing the specific procedure for boiling-and-discarding and soaking in water.
Effect on the Taste and Flavor of Marmalade by Combining Citrus Fruits
Checked for this overview: The part introducing the figures for the decrease in naringin and the increase in nomilin.
Other names: アルベド（中果皮・白いワタ） (ja)
Hypotheses and recipe candidates for this entry are on the Japanese page.
Structured claims — open a section to read each claim's confidence, evidence and limits
Composition and content (1)
Scope: Histological and chemical research on the yuzu outer peel and mesocarp (albedo) by Kuwada and colleagues, Journal of Cookery Science of Japan, volume 48, issue 2.
Note: Kuwada (2015) measured naringin as a bitter constituent in 2 fractions: flavedo (outer peel) and jelly ingredients (a mixture containing albedo, endocarp and pulp). Neither the text nor the figures of this paper state that the white pith (albedo) holds more naringin.
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ingredient-yuzu-peel —has_perceived_bitterness_associated_with→ "Bitter constituents such as naringin released from the peel (material containing both the flavedo and the mesocarp)."Mechanism and receptors (1)
Scope: A review of citrus marmalade processing by Kuwada (2015).
Note: The review’s opening statement 「柑橘マーマレードを製造する際、加熱によって苦味の生成が起こる」 (in translation: "When making citrus marmalade, heating generates bitterness") is a secondary summary based on the cited Miura and Araki (1988) and Yuge et al. (1993) papers. Those primary papers were not directly checked in this investigation.
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ingredient-yuzu-peel —has_perceived_bitterness_affected_by→ "The processing step of heating to make marmalade or similar products."How processing and cooking change it (2)
Scope: An explanatory article on preparing yuzu peel in 「丸ごと小泉武夫 食マガジン」 (Marugoto Koizumi Takeo Shoku Magazine).
Note: A how-to article on a food-media website. It says "even jam or yuzu tea will not be bitter", but no sensory evaluation or chemical analysis accompanies it, and it does not compare bitterness with and without removing the white pith.
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ingredient-yuzu-peel —has_perceived_bitterness_suppressed_by→ "Boil, scrape off the white pith, then soak in water."Scope: A 1994 marmalade process using yuzu peel (Morishita 1994).
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ingredient-yuzu-peel —was_observed_with→ "Water soaking and heating reduced naringin by 63–76%, while nomilin increased from 5.4 to 15.8 ppm."