why'd my steamed broccoli turn brown?

August 6, 2024 8:01 AM

I got some broccoli (sauteed with garlic) from the grocery store's prepared foods section, but I like my brocco a bit mushier, so I briefly steamed it in the instant pot - which made it turn brown! (image) This is not a "should I eat it" post, just a "why'd it do that?" I've steamed a lot of raw broccoli in my time, but I don't think I've tried it on sauteed before.
posted by moonmilk to Food & Drink (9 answers total)

Update: I tasted the steamed sauteed broccoli and it's absolutely disgusting! What happened!?

Good thing I still have some un-ruined broccoli left to save my lunch.
posted by moonmilk at 8:05 AM on August 6

blanching is recommended over steaming, as well as adding salt: "Salt provides a “barrier” against carbon dioxide, which prevents chlorophyll from changing color." [whiteapronblog]
posted by HearHere at 8:10 AM on August 6

Green veggies can turn brown during cooking due to acidic ingredients and lower pH. This can be "rescued" with alkaline ingredients like baking soda but that offsets the deliciousness of some more acidic dishes. Here's a recipe with a little color experiment that stuck in my brain several years ago.

But based on your update, I'm wondering if you're tasting different sulfur compounds that are produced as the garlic aromatics break down. High heat and fast cooking is sometimes cited as bad for garlic flavors.
posted by fountainofdoubt at 8:13 AM on August 6

nthing the taste may be the garlic - garlic goes from delicious to 'burnt', bitter, disgusting in seconds.
posted by koahiatamadl at 8:25 AM on August 6

As someone who steams broccoli almost every day, plain, I've only seen it start to turn brown when I accidentally let it get way smushy/overdone and it's usually inedible. (I've been better about setting a timer recently!)

It looks a bit like soy sauce on it? My guess is that it's something that was added to it.
posted by Glinn at 8:38 AM on August 6

I steam broccoli in the microwave pretty often. My process is the same every time -- but very very occasionally, it will turn brown. While I haven't tested this, my sense is that when this happens, the broccoli in question has been sitting in my fridge for a while. The weird thing is, that not all older broccoli does this, it only happens sometimes.
posted by OrangeDisk at 9:01 AM on August 6

My understanding is that the instant pot is sealed for "steaming." This makes it effectively the same as most any other kind of pressure cooking, which is to say not much like the gentle light cooking ordinarily implied by "steaming." So you put mostly-cooked broccoli into the instant pot and pressure cooked it which, even for a relatively short period of time, was sufficient to badly overcook the broccoli. The overcooking, in addition to the instant pot being a closed system, allowed acid to react with the chlorophyll which created the brown coloring. You never really want to cook cruciferous vegetables in a closed system. That's why you want continuous venting if you're going to steam them.
posted by slkinsey at 11:51 AM on August 6

I kept the vent open for the instant pot’s steam mode, but it’s still a lot closer to being a closed system than, say, a rice cooker.

I don’t know if we have a consensus here, but it seems like acidity plus heat plus a nearly enclosed environment add up to nasty broccoli and denatured garlic. I won’t do it again!
posted by moonmilk at 1:56 PM on August 6

I recognise this description from my Mum’s 1980s “chow mein”
posted by slightlybewildered at 11:08 PM on August 6