http://revach.net/tefila/article.php?id=1141

Section: Halacha   Category: Tshuvos
Brachos Question: Food Stuck Between Your Teeth, Do You Make A Bracha?

What is the Halacha if after eating and making a bracha acharona you have food stuck between your teeth; do you need to make another bracha before swallowing it? The Shevet HaKehosi paskens (1:95) that since this food is no longer considered food you do not make a bracha on it.

He distinguishes this case from the case where you ate food and forgot to make a bracha. If it is still in your mouth and cannot be spit out since it is already chewed you put it to the side of your mouth and make a bracha. In that case he says although the chewed food is not considered food for the purpose of making a bracha on it, the bracha you make is going on the food from before it entered your mouth which was real food. Although you are a little late to make a bracha and should have done so before putting in your mouth, since it is still in your mouth it is not yet too late to make a bracha.

Disclaimer: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.