Which of the following practices helps ensure guest safety in food service?

Using a clean spoon for each sampling is essential for ensuring guest safety in food service. This practice minimizes the risk of cross-contamination and the spread of harmful bacteria or allergens. When guests sample food, especially in buffet-style settings or tastings, employing a new, clean utensil for each sample prevents the transfer of saliva or germs from one person's mouth to the communal food. This is particularly crucial in settings where allergies to certain ingredients may be a concern, as cross-contact can lead to serious health issues for sensitive individuals.

In contrast, allowing guests to serve themselves can increase the risk of contamination, especially if they do not use proper hygiene practices. Sampling from shared dishes can also be risky as it exposes food to multiple individuals, which can lead to the rapid spread of pathogens. While choosing plastic utensils might be safer in certain circumstances (for instance, avoiding breakage), it does not inherently address the hygiene issues that can arise during food sampling. Therefore, using a clean spoon for each sampling is the most effective practice for ensuring guest safety.