If you're in a moderate to severe flare, you're going to experience symptoms almost regardless of what you eat because of the amount of inflammation. Just about
anything passing through is going to irritate an inflamed colon, unless you go on a predigested liquid diet to allow for bowel rest.
In my experience, you have to limit yourself to a very easily digested, safe diet while also healing the colon with supplements and rebalancing the gut with probiotics. And you have to allow plenty of time to heal. Cutting out a suspicious food for a few days probably isn't going to have much effect. For example, the Specific Carbohydrate Diet recommends faithfully following the diet for at least a month and up to several months before deciding it doesn't work for you. I'd also add that, although I've been tested for celiac disease and gluten intolerance and tests have come back negative, I know from my own experience and keeping a food journal that eliminating or severely restricting all grains helps me maintain remission.
Diagnosed with ulcerative colitis spring 1999.
Maintenance dose sulfasalazine. Probiotics, l-glutamine, vitamin D and fish oil caps. George's aloe vera juice. Oregano oil antibiotic, antiviral, antifungal. Mostly grain-free and dairy-free diet. Long-term remission with only minor blips.