Make It Yourself: Guide to homemade mustard with some science

In it’s simplest form, mustard is the product of two components; mustard seeds blended with a liquid. The range of concoctions and room for exploration however, is vast. To begin with you have the type or combination of seed. Then the type of liquid you immerse those seeds into. Finally you have any additional ingredients you may want to experiment with. Not only do you have the physical components that make up mustard, you also have the processing components. How long you soak the seeds for, how fine you grind the seeds, whether you strain or not, each step has a varying effect on the final mustard.

The Science

The heat experienced by mustard is neither a smell nor a taste, it is a sensation, a pain response. It engulfs our mouths and nasal passageway in a short and sharp sensation of irritation. The notable difference in the kind of heat generated by mustard and it’s relatives wasabi and horseradish, compared to that of the heat experienced by chillies and peppers, is down to chemistry.

A colourless oil called isothiocyanate is the culprit responsible for the pungency in mustard and it’s relatives. A defensive mechanism for plants, isothiocyanates form when the plant or seeds aBase Recipe for Simple Homemade Mustardre under attack or become damaged. When the plant or seed is damaged the enzyme myrosinase and its natural substrate the glucosinolates, which work together to produce the deterrent isothiocyanate, however, we’ve kind of evolved to love the sensation it produces. These isothiocyanates are a small and light compound and readily escape from food into the air, thus they move quickly from our mouths as we chew, and go up and into our nasal passageway and mildly damage the unprotected cell membranes through-out their journey, producing that fiery sensation that centralises itself so violently in our noses.

Chillies, peppers and a host of other foods however, are from a different class of pungent chemicals, the alkylamides. These are heavier and larger molecules. They centralise within our mouths because they’re less prone to escaping food and into our nasal passageway. They work differently in that they bind to receptors on cell membranes which trigger pain signals in the brain.

Components of Mustard

The Solids – Seeds

Black – Brassica nigra

The most pungent of the bunch, black mustard seeds are rich in the glucosinolate compound sinigrin. Singrin breaks down into a mustard oil which is the irritant stimulant responsible for the burn.

Brown – Brassica juncea 

A more familiar seed, it’s lower in sinigrin thus “less” pungent than it’s black counterpart.

Yellow/White – Brassica hirta

The most familiar, these seeds contain a different glucosinolate, the weaker, less pungent sinalbin.


Using mustard powder will give finer more runny mustard, similar to that of and English mustard.

The Liquid

Mustard can be made with an array of liquids. The more acidic that liquid, the slower the disappearance of the pungent compounds. This is due to the slowed activity of the enzymes, giving you a longer lasting slow burn.

Those made with less acidic liquids speed up the enzyme activity, giving you more heat but far quicker when freshly prepared. So bear in mind, the more water, the more violent, and so it’s best as fresh as possible to maintain that kick before it’s lost.

Notes for Cooking With and Storing Mustard

You’ll notice a big difference when cooking with these two classes of pungent chemicals. Chillies and the like hold their heat when cooking whereas if mustard is added early on in a dish and cooked, it’ll lose it heat due to the heat inactivating the enzymes. Thus, if you want a kick from mustard, add it at the end of cooking, if not and you want that bitter and nutty flavour hidden behind the heat, add it earlier on.

The antibacterial properties of mustard means it won’t develop mould or harmful bacteria, so long as you haven’t mixed in any crumbs! etc. So if you’ve had a jar lying around for a while, it’s doesn’t need to be thrown into the bin. It’ll be fine. It may lose its pungency over time, even if created with an acidic liquid. To help, store in a dark and cool place, and if it loses its bite mix in a small amount of acidic liquid, like vinegar or wine.


Base Recipe for Simple Homemade Mustard

A simple recipe for making your own homemade mustard. From here you can explore with different seed combinations, additional flavours or test out different immersion liquids

Course Condiments


  • 100 g seeds any combination of colour
  • 150 ml acidic liquid cider vinegar, wine, beer etc
  • 100 ml water


  1. Take your preferred solid - seeds, a mix or powder. Soak for 24-48 hours in the liquid mix of your choice. They'll double in size, so a bowl with plenty of space. Soaking helps develop the pungency and makes processing easier

  2. Once soaked, blend the seeds and liquid in a food processor or blender. Blend to the consistency you prefer, longer will be finer and more like an English or Dijon mustard, shorter will give you a wholegrain type of mustard.

  3. Pop into a sterilised jar and enjoy.

Recipe Notes

There is a tonne of room for experimentation, so during the blending try adding different herbs and spices. If you want a bright mustard, turmeric will give you a bright yellow colour. For sweetness try adding a couple of tablespoons on honey.


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