Macaroni Salad

Macaroni salad keeps 3–4 days refrigerated and does not freeze — the pasta turns mushy and the dressing separates.

Cool the pasta completely before dressing it. Warm pasta stirred into mayonnaise makes a large bowl of lukewarm starch, which is the exact condition the storage rules exist to prevent. Rinse cooked pasta under cold water, drain thoroughly, and chill it before mixing.

At a picnic or barbecue, keep the bowl nested in ice and observe the two-hour cumulative limit — one hour if it is above 90°F. This is the dish most often left out longest at outdoor gatherings, and it should not be.

Store it in a shallow covered container so it stays properly cold throughout, and take out only what will be eaten.

Macaroni salad is the food most often blamed for picnic illness, and it is a fair target — but for the pasta, not for the mayonnaise.

Cooked pasta carries Bacillus cereus, a spore-forming bacterium common on grains whose spores survive boiling. When cooked starch sits in the growth range, those spores germinate and produce cereulide, a heat-stable toxin. A bowl of pasta salad sitting on a picnic table for four hours is close to a textbook illustration of the conditions B. cereus needs.

The dressing, meanwhile, is doing the opposite of what folklore claims. Commercial mayonnaise is made with pasteurized eggs and acidified with vinegar or lemon juice to around pH 3.6–4.0, which makes it mildly inhibitory to bacterial growth. It lowers the pH of the salad slightly.

The other contributor is handling: chopping vegetables, mixing by hand, and repeated serving with a shared spoon all introduce Staphylococcus aureus, whose toxin is likewise heat-stable.

So the control is temperature, not ingredients. Keep it cold, keep it covered, and observe the two-hour total.

Signs of spoilage are a sour or fermented smell, a fizzy or bubbling appearance, sliminess, and liquid that has gone cloudy or ropy.