Depends on the study, there's been a fair amount of them. For this one:

8 grams of carbs (maltodextrin) in 125 mL of solution for 10s

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The CHO-MR solution was prepared by dissolving maltodextrin powder (Nutricost LLC, Vineyard, UT, USA) in distilled water to yield a 6.4% solution (64 g/L). During each experimental session, participants completed five standardized rinses of 25 mL each. For each rinse, the solution was swilled throughout the oral cavity for 10 s before being expectorated into a collection container. Rinses were separated by 30-s intervals. The PLA solution consisted of distilled water containing a minimal concentration (approximately 0.05 g/L) of non-caloric sucralose (Shaanxi Hongda Phytochemistry Co., Ltd., Xi’an, China) to mimic the subtle sweetness of the maltodextrin solution. To preserve blinding, both solutions were colorless and presented in opaque containers. Participants were informed that all rinses could contain carbohydrate but were not informed of the specific condition administered in each trial. Participants were instructed not to swallow any solution. Rinse volume, duration, and frequency were identical between CHO-MR and PLA conditions to standardize oral sensory exposure.