Eight clues are thematic and are clued by word-play only. Each of these eight clues' word-play has an extra letter which is not part of the answer. These letters cryptically indicate something, which when put together with the theme, one might expect to drink when enjoying the theme. This (three words, (7,9,3)) must be stated to complete the puzzle. All other clues are normal.
Across
8. Made an effort to follow beef rump (5)
9. Interrogate leaders of Turkey's 'egg' deliverers (7)
10. Fifty-one and a third of cereal parasites (4)
11. Chewed acorns and crushed dacite (10)
12. Reseated as a guest with starter of soup (8)
15. Baker's friends give direction in heartless agreement (6)
16. Electronic consent for Peeps (4)
18. Kiln for drying hops decorated with trout skin (5)
19. Stop crown of celery going off and relax (4)
21. Second ovary boiled with herb (6)
23. Moët 18 (sparkling!) (8)
25. Oven-cooked batter with hint of nigella and last of bangers (5,5)
28. Municipal egg-boxes turn whitish (4)
29. Swore and turned aside to trade rabbit's foot for its head (7)
30. Flutter an eyelid at wedge of cheese and bone marrow (5)
Down
1. Loud in icy café? Upheaval is able to produce the intended result (8)
2. Is bell rung for defamatory statements? (6)
3. More than half of soy beans are used for cheese (4)
4. For example entrails are not for everyone (4)
5. Note-density is variable -- plug music players in vertical stack (4-6)
6. The act of removing obvious half of lovage (8)
7. Coming in the year of our lord -- pie opening... (6)
13. ...try eggs (but scrambled) at famous address? (10)
14. Sparing cutting, withdrawing cheesewire finally (5)
17. Maybe beach workers abolish or emend holding (8)
20. Quiet and Latin -- country of islands (8)
22. Scoundrel and woman returning for manifestation of Shiva (6)
24. Themes of Optics discussed (6)
26. Verdi's work to help introduction of asparagus (4)
27. Weeps noisily: first of all save our breakfast sandwiches (4)
