(part of the Secret Pro Techniques ramen nerdery research series)

@Elvin Yung <@shikaku.ramen>

The short, easy way to think about hydration is that it's the percentage of water added to make a noodle, usually indicated as a baker's percentage of the flour component. But peeling back the curtain, there's a little bit more complexity in the concept.

Can you handle the truth?

To properly discuss hydration, one concept that's important to clarify is the idea of kansui. We typically think of kansui as just the alkaline component of the liquid ingredients, usually the sodium carbonate and/or the potassium carbonate that gets mixed with salt and water to form the liquid ingredient mix. But kansui is not just kansui.

In Japanese (and Chinese), kansui quite literally just means alkaline water, which means that it refers both to the alkaline compounds (which historically naturally occurs in liquid form), as well as the mixture of alkaline compounds, water, salt, and other adjuncts that might get added to noodles (which may include things like eggs, oil, alcohol, etc.).

For the sake of clarity in the rest of this article, I'll use the term "alkaline compound" to mean the actual basic (literally) alkaline components, and "kansui mixture" to refer to the liquid ingredient mix that gets added to the flour during the mixing process.

Japanese noodlemaking tends to use the Baumé scale to measure the alkalinity of a kansui mixture, which measures the specific gravity and therefore the concentration of dissolved solids in a solution. This is in opposition to the American ramen making community, which generally defines a kansui mixture in terms of predefined amounts of water, salt, alkaline compounds, and other adjuncts. To distill this idea further, the Japanese measurement system is designed for "post hoc" dilution by adjusting Baumé, while American measurements are predicated upon an assumption of predetermined, "a priori" dilution, where the amount of kansui mixture is known in advance and directly matches the amount of noodles made.

The Japanese system seems backwards, there are a few reasons why it makes sense. First, historically kansui would have been an inseparable solution of alkaline compounds in water, which means that it would have been impossible to account for hydration and kansui separately. Secondly, 1g of sodium carbonate in 30g of water is less alkaline than 1g of sodium carbonate in 40g of water, so by relying on the density, you're essentially ensuring that the kansui mixture has the same alkalinity no matter at what hydration level.

But it makes the most sense you when think about a noodlemaker's workflow at scale: to streamline things, a noodlemaker might premix huge batches of kansui mixture so that it can be reused across multiple batches of noodles. But this also means that at the time that the noodles are being mixed, the only two numbers that are known are how much flour is used, and how much of the kansui mixture is used. This means that while it's easy to figure out how much of the kansui mixture was used for each portion of noodles, it's also very hard to figure out how much actual water and alkalinity went into each portion of noodles.

This is important, because it means that we don't really know how hydration is actually calculated.

Yokohama Raumen Museum's online dictionary defines 加水率 (kasuiritsu) as the proportion of water in noodles, but it also notes an adjacent concept, 総加水率 (soukasuiritsu), which is the proportion including things like salt, kansui, eggs, and other adjuncts. Japanese literature, however, inconsistently switches between those two concepts:

• Yamato uses the total kansui mixture to form its main hydration percentage.
• The book Ramen Gijutsu Kyouhon (ラーメン技術教本) doesn't really talk about hydration percentages in the specs that it gives, but describes ingredient mixes in terms of the entire kansui mixture, implying (but not confirming) that the hydration is composed of the whole kansui mixture.
• Chuka Soba NEO (中華そばNEO), even more confusingly, gives specs with a stated hydration percentage that consists of just the water, but then adds other hydrating components (e.g. whole egg) on top of it.

If anything is clear at this point, it's that hydration is really two different concepts, often conflated: a net hydration that refers just to the amount of water in a noodle, and a gross hydration that includes all these other ingredients that get mixed into the liquid ingredient mix.