As an alternative view, I would be conservative here. When an expense is both personal and business, you have to allocate the percentages and only claim the business portion. This is most easily seen with business use of a personal car, where you allocate your expense based on mileage. A sort-of-related example involves deducting medical expenses. Suppose a paraplegic person buys a car with a hand control conversion. Even though the hand controls are medically necessary, the entire car isn't a deductible medical expense, just the extra cost of the conversion compared to the normal car. Lastly let's look at the origin of the 50% rule. You can deduct 50% of your meals when traveling for work, but not when working in your home city. That's because you have to eat when you are home and eating is a non-deductible personal expense, you can't deduct your lunch just because you buy it at a cafe instead of brown-bagging it from home. But when traveling, your meal costs are recognizably higher -- you are away from your kitchen, you eat out more, etc. So the IRS recognizes 50% of your meal costs as a travel expense when you are traveling away from home for work purposes.
Applying these principals to food blogging suggests you can only deduct the extra cost compared to eating personal meals. The 50% rule might be a good compromise.
As I said, that's a conservative approach, and I am not your accountant paid to stand behind you in the rare chance you are audited.
