Pasteurization and Namazake: Understanding Nama, Namazake, Namachozo, Namazume, and Muroka Nama Genshu

"Namachozo-shu" and "namazume-shu." The names look almost identical, and plenty of drinkers can never remember which is which. In fact, the two differ in only one respect: at which of two identical pasteurization steps the brewer skips the heat.

Hi-ire, or pasteurization, is a brief heat treatment. Most sake passes through it twice during production. Which of those two passes gets skipped is exactly what splits sake into namazake (unpasteurized sake), namachozo-shu, and namazume-shu. This article walks through why pasteurization exists, how to tell the three "nama" (raw/unpasteurized) styles apart, and how to unpack the mouthful that is "muroka nama genshu." Follow that path and the raw-sake terms on any back label stop being a puzzle. For where pasteurization sits in the wider brewing sequence, see the production process; for handling and storage details, see storage and temperature.

What pasteurization is for

Hi-ire is a brief heat treatment applied to pressed sake, typically around 60–65°C (140–149°F). It serves two purposes: suppressing hiochi bacteria and deactivating residual enzymes.

Hiochi bacteria are an unusual strain of lactic acid bacteria that can survive in sake. Most microorganisms can't tolerate its alcohol and acidity. Left unchecked, they cloud the sake, turn it sour, and make it unsellable. This spoilage is called hiochi. Heat kills the bacteria and halts their growth.

The second target is enzymes. Freshly pressed sake still carries active enzymes derived from koji (mold-cultured rice). Left alone, these enzymes keep nudging the flavor and aroma in new directions over time. Pasteurization deactivates them, locking in the taste the brewer was aiming for.

Overheating, though, is a real risk. Push the temperature too high and alcohol boils off while the aroma gets damaged. So pasteurization isn't a long, hard boil. It's a short pass through a target temperature range.

Breweries use a few different methods. Bin-bi-ire submerges bottled sake in hot water. Jakan pipes the sake through thin coiled tubes run through hot water. A pasteurizer runs it continuously through a heat exchanger. Which method a brewery picks depends on its scale and the character it's after. Bottle pasteurization, for instance, tends to preserve aroma better and keep some of namazake's freshness. Whatever the method, the goal is identical: suppress hiochi bacteria and stop the enzymes. For where this step falls in the overall brewing sequence, see the production process.

Two pasteurization passes, and where the split happens

Standard sake is pasteurized twice: once after pressing, before storage, and again just before bottling and shipping. Sake that goes through both passes is stable enough to sit at room temperature through distribution. Most bottles on a typical shelf are this type.

Which "raw" category a sake falls into depends on which of those two passes gets skipped. There are three possible combinations:

• Skip both passes: this is namazake.
• Skip only the pre-storage pass: this is namachozo-shu.
• Skip only the pre-shipping pass: this is namazume-shu.

When in doubt, look at what the "nama" (raw) in the name is modifying. In nama-chozo-shu, chozo means "storage," so it's the storage stage that skips pasteurization. In nama-zume-shu, zume means "bottling," so it's the bottling stage that skips it. The name itself tells you which step was left unheated.

Namazake: no pasteurization at all

Namazake (literally "raw sake") skips pasteurization at both stages (before storage and before shipping). It's also called honnama ("true nama"). With no heat treatment whatsoever, its calling card is the fresh, vivid aroma and juiciness of sake straight off the press.

Japan's National Tax Agency, in its labeling standards for sake ("Seishu no Seiho Hinshitsu Hyoji Kijun"), defines namazake as sake that has never been heat-treated after production is complete. So a "namazake" label means, by definition, zero pasteurization.

That freshness comes with a caveat. Because the koji-derived enzymes are never deactivated, namazake keeps changing. Its flavor can shift noticeably within a short time at room temperature. Refrigeration is essential, and it's meant to be drunk soon after opening. Handling details are covered at the end of this article and in storage and temperature.

Namachozo-shu: raw through storage, pasteurized once before shipping

Namachozo-shu ("raw-stored sake") skips pasteurization during storage and is heat-treated only once, at bottling. That means exactly one pass of pasteurization, timed right before shipping.

Because it sits unpasteurized through the storage period, it retains a fair amount of namazake-like freshness. Since it does get pasteurized before shipping, though, it holds up better in distribution than true namazake. The labeling standard defines it as sake stored without heat treatment and then heat-treated at the time of shipment. Its relative durability is why it's a common choice for small bottles and single-serve cups.

Namazume-shu and hiyaoroshi: pasteurized once before storage, raw at shipping

Namazume-shu ("raw-bottled sake") is heat-treated once, before storage, and then skips pasteurization at bottling. That's the same single pass as namachozo-shu, just at the opposite stage.

Hiyaoroshi, the sake that appears on shelves in autumn, is the classic example of namazume-shu. Sake pressed in winter is pasteurized once in spring, then aged through a full summer. Come autumn, it ships without a second pasteurization, bottled raw. Having mellowed over the summer, it's prized for its rounded, settled flavor. Hiyaoroshi and other seasonal releases are explored further in sake through the seasons.

Namachozo-shu and namazume-shu both involve exactly one pasteurization pass. The difference is simply which stage skips the heat. The comparison table below lines them up side by side.

Quick-reference table: the pasteurization split

Here are all four categories, organized by whether and when pasteurization happens, along with which stage the "nama" (raw) in each name refers to. Bookmark this table for whenever a back-label term throws you.

Looking only at the count, namachozo-shu and namazume-shu are tied at one pass each. The difference lies entirely in which stage skips it. Keep that single distinction straight and you'll never mix the two up again. As for freshness, namazake (zero pasteurization) is the most vivid, followed by namachozo-shu and namazume-shu, with twice-pasteurized sake being the mellowest of all.

One more clue worth knowing: sake that skips any pasteurization step often carries a "keep refrigerated" notice on the back label, and true namazake (zero pasteurization) is almost always labeled this way. If the terminology doesn't click right away, checking the storage instructions is a reliable shortcut to figuring out whether a bottle is some form of nama.

Unpacking "muroka nama genshu"

"Muroka nama genshu" is a mouthful, but there's no need to be intimidated. It's just three separate terms stacked together, each one flagging a different step that was skipped.

Put all three together and you get muroka nama genshu: sake that's had nothing taken away, about as close as it gets to what came straight off the press at the brewery. Because genshu skips dilution, its alcohol content runs higher, typically 17–19%, versus roughly 15% for standard, water-adjusted sake. Dilution normally exists to bring the alcohol to an easy-drinking level and round out the flavor; skip that step, as genshu does, and both flavor and aroma tend to come through more intensely.

One caveat on the terminology: "genshu" and "namazake" are official labeling terms formally defined in the National Tax Agency's standard. "Muroka," by contrast, has no such definition. It's a voluntary term breweries use to describe their process. Even when all three appear together on one label, they don't carry the same legal weight.

Handling and storing namazake: refrigerate and drink it soon

Any sake that skips pasteurization needs more careful handling than fully heat-treated sake. As covered above, the reason is that its enzymes remain active and its flavor keeps shifting. True namazake (zero pasteurization) changes especially fast, so leaving it at room temperature is best avoided.

The storage guide from Japan's National Research Institute of Brewing (NRIB), the national body responsible for sake research, recommends keeping namazake cold, roughly 1–5°C (34–41°F). Refrigerate it as soon as you buy it, and once opened, drink it promptly. That's the surest way to preserve namazake's signature freshness. Namachozo-shu and namazume-shu, having gone through one pasteurization pass, are more forgiving than namazake but still call for earlier consumption than fully pasteurized sake.

"It's raw, so it must be fresh and fine at room temperature" is a common misconception. The rule runs the other way: the more "raw" a sake is, the more it needs to be chilled and drunk soon. Keep that one principle in mind and you can enjoy the character of any unpasteurized sake as it's meant to be tasted. Which temperature suits which style, along with home storage steps, is covered in storage and temperature. For a walkthrough on spotting raw-sake terms on a back label, see how to read a label.

From namazake, which never sees a drop of heat, to fully pasteurized sake that's been through the process twice, this range shows just how deliberately sake's flavor profile can be engineered. Next time you're choosing a bottle off the shelf, recalling how many times it's been pasteurized will tell you a good deal about the character waiting inside.

• This article is intended for readers of legal drinking age (20 in Japan). Please drink responsibly. Avoid alcohol during pregnancy or breastfeeding, and never drink and drive.