For the first time in many years, there are enough red bell peppers in the harvest for me to make this recipe for roasted red pepper mustard, which I have made off and on for 20 years or so.

It's been a long time since I've made it, and there's one aspect that didn't always work.

As you can see, the recipe involves

A) mixing .75c dry Colman's mustard (or equivalent) with 2.5c water+vinegar. let it sit.

B) boil 1 1/6c sherry+wine for 7 min (reduces it some, but not a whole lot)

C) mix A+B, cook in double-boiler until thick.

D) stir in red pepper puree.

My memory is that sometimes step A thickened up while it was resting, and sometimes it didn't. When it didn't, no later step ever really got thick enough. And that was a pity, because the mustard is incredibly delicious, kind of pricey to make, but makes a super gift if it sets properly.

Could the difference be that sometimes I substitute Penzey's regular mustard powder for the Colman's? Would Oriental mustard powder do instead? Or do I need to just resign myself to buying Colman's in bulk? I like to make a lot of this stuff.

  • step B would reduce differently depending on what size pan you used. (that's why recipes often say 'reduce to 1 cup' or 'reduce by half' rather than just an amount of time.). This might not matter because of step C, but I'm not sure.
    – Joe
    Sep 16, 2014 at 19:35
  • The instructions for Colman's mustard powder suggest it should be mixed equal parts powder to cold liquid, so I'm not really suprised that 0.75c to 2.5c results in a thin mixture.
    – Allison
    Sep 23, 2014 at 19:43

2 Answers 2


Could the problem possibly be due to the variation in the amount of starch in the mustard used from batch to batch of your own making, so its thickening quality varies each time? Or could it be stale stock?

According to their website, Colman's mustard is made from 60% locally sourced yellow mustard seed and quality controlled, so it is fairly constant from year to year and has been since 1814. At least we presume it has remained so the whole time since Unilever took over in 1995 and was the case beforehand.

Working on that presumption, using the other brands or types of mustard (such as black, brown or oriental) could be the issue for you. Or have Unilever decreased the English yellow mustard content to 60% so there have been inconsistencies since 1995? I guess you would have to ask them directly to eliminate that as a possible cause.

According to Canadien researchers, yellow mustard seed contains 20% to 30% protein, 24% to 35% oil, 6% to 12% lipids and 12% to 18% carbohydrates, but according to this source the starch content is fairly minimal at only 0.6 g per ounce. Although that seems a slight amount and small variation range respectively, it may still influence your mustard making. If this proves to be the problem, you could add and cook off plain flour to cure "thin" mustard or increase the mustard powder content.

I hear what you say about the cost of good imported English mustard. Have you considered sourcing whole English yellow mustard seeds and grinding them yourself? I was considering that myself, after I looked everywhere for Colman's this summer, but 113 g / 4 oz containers are the biggest on supermarket shelves and even then they are only rarely in the larger stores. I hate the tiny (relatively expensive) tins, so it looks like I'll have to buy via the internet or visit the Colman's shop in Norwich to finally get a pound sized tin. Still a visit to a museum is always interesting. Especially when food-related. I'll be needing a bulk supply, with winter coming soon...

Illustration for Colman's Mustard by John Hassall

«John Hassall (1868–1948): Colman’s Mustard Advert, 1899»


It sounds to me like your bigger sources of thickening is the pectin in your red peppers- it would also be your biggest source of variability. Peppers will have more pectin and sugars if they are ripe, and will thicken nicely, but ultimately, nature makes these things pretty fickle, and if they happen to be unripe, or just plain grumpy, they may not have much pectin at all.

This recipe sounds delicious, so I wouldn't change it one bit. What I would do is after I added the red pepper puree, I would take a teaspoon and put it on a plate in the fridge or freezer, just to see if it gels when cold. If it doesn't, I would add a teaspoon of pectin to the pot, and repeat the cooling test. You can buy pectin powder in little sachets from your supermarket, probably next to the gelatin.

  • The pectin theory is interesting, but the way I read the question, in the first step only mustard, water and vinegar is mixed, and it is this mixture which doesn't always thicken.
    – rumtscho
    Oct 3, 2014 at 11:03
  • Ah, you're right, the question is about the mustard, not the final product. To be fair, adding more thickener couldn't hurt, and pectin is fairly shelf stable. Oct 3, 2014 at 11:11

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