How do I convert a powdered seasoning into cube (bouillon) form?
In order for your powdered seasoning to hold together in a solid shape, two things are needed.

1. Added ingredients that will work as a binder.

Commercial bouillon cubes are made by adding some sort of saturated fat that is solid at room temperature, such as partially-hydrogenated palm or cottonseed oil. Corn or other modified food starch may also be added, along with sugar, and of course, lots of salt.

You might be able to achieve a similar effect using beef tallow, coconut oil, or lard. Without chemical preservatives however, the result would need to be refrigerated. 

2. A device to compress the mixture via intense mechanical pressure.

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Bouillon cube factories use large presses to form the mixture into cubes, but of course, such machinery is not available for home use.

Instead, you could compress your mixture into cylinders using a "pollen press". This model costs about $20 and will make cylinders about the diameter of a nickel.

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So, you need to decide whether you really want to adulterate your special blend of seasonings with added binding ingredients — ingredients which may affect the flavor and shelf life of your seasoning. You also need to decide whether the extra work of compressing the mixture into a solid shape is really worth all that trouble.



Another possibility that might work better for you would be to put your powdered seasoning directly into empty gelatin capsules.

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Such capsules are made from beef gelatin — an ingredient that seems quite appropriate for use in bouillon!

Dropped into hot liquid, the flavorless gelatin capsules would quickly dissolve and release your powdered seasoning.

If you need a vegan alternative, empty vegetarian capsules are also available. Made from a derivative of vegetable cellulose, they dissolve in liquid just like gelatin capsules. However while gelatin is basically flavorless, vegetarian capsules may add a detectable taste. The taste may vary by brand, and depending on the intensity of your own seasonings, it might or might not be an issue.

Both types of empty capsules are sold in various sizes, and there are special trays and other tools available to facilitate filling them with powder. Refrigeration is not necessary, and the shelf life your dry seasoning would be protected inside the capsules.