The Sake Anatomy › Sake Brand Index › Gunma Izumi
No.106 · Brewery Profile
Gunma Izumi群馬泉 · Shimaoka Shuzo 島岡酒造
Shimaoka Shuzo is one of the last breweries anywhere still practicing true kimoto-kei yamahai fermentation — cultivating lactic bacteria naturally rather than adding acid or a pre-made starter. Everything is aged a year or two before release, drawing out a rich, concentrated umami and pronounced acidity that stands apart from the smoother, faster styles most modern breweries favor, brewed on spring water from the Akagi mountains.
Who makes Gunma Izumi?
Shimaoka Shuzo has brewed since 1863 and is one of the last breweries anywhere still practicing true kimoto-kei yamahai fermentation, cultivating lactic bacteria naturally rather than adding acid or a pre-made starter. Everything is aged a year or two before release, using spring water from the Akagi mountains.
What does Gunma Izumi taste like?
Tagged Rich & Umami and Acidity-driven, all three bottles are junshu (rich) in SSI terms with pronounced acidity from natural yamahai fermentation. The Daiginjo is long-aged for a fine texture and deep flavor; the Junmai Ginjo carries sharp yamahai acidity with complex umami; the Yamahai Junmai, the signature everyday sake, is the fullest and most acidic of the three at 4/5.
Which bottle should you try first?
Start with the Yamahai Junmai, explicitly the brewery’s signature yamahai-style everyday sake.
How does Gunma Izumi compare to other Gunma breweries?
Gunma’s only other brewery in this index, Mizubasho, sits at the opposite end of the prefecture’s range, tagged Aromatic & Fruity and Elegant & Refined, while Gunma Izumi leans into Rich & Umami and Acidity-driven instead.
Frequently asked questions
What brewing method defines Shimaoka Shuzo?
True kimoto-kei yamahai fermentation, cultivating lactic bacteria naturally rather than adding acid or a pre-made starter — one of the last breweries anywhere still doing so.
How long is Gunma Izumi’s sake aged before release?
A year or two, drawing out rich, concentrated umami and pronounced acidity.
What water does Gunma Izumi brew with?
Spring water from the Akagi mountains.
The bottles
Daiginjo大吟醸
醇酒 Junshu · Rich“Long-aged for a fine texture and deep flavor.”
Junmai Ginjo純米吟醸
醇酒 Junshu · Rich“Sharp yamahai acidity with complex umami.”
Yamahai Junmai山廃純米
醇酒 Junshu · Rich“The brewery’s signature yamahai-style everyday sake.”
Reading the bars: an editorial flavor reading (0–5) of each bottle — Dry→Rich, Light→Full, Subtle→Aromatic, Low→High acidity — not laboratory values. The colored badge is the SSI four-type classification (薫酒 Kunshu · 爽酒 Soshu · 醇酒 Junshu · 熟酒 Jukushu). SMV and acidity appear only where the brewery publishes them.
Sources: shimaokasyuzo.com · sakeworld.jp