This is one of her five dinner ladies, Jean (played by Anne Reid), recalling a recent wedding: "Auntie Dot from Cockermouth ate a raffia drinks coaster. Thought it was a high-fibre biscuit. She had to be held back from moving down the table and buttering two more."
Bennett might have avoided the third bite at the same joke. But Wood's approach plays to all the strengths of the sitcom, a widely-watched if rarely admired form. She uses language with relish, yet can make her points concisely. Oh yes, and she's funny - something you can't say about most sitcom-writers. All of which makes Dinnerladies the most satisfying new sitcom of the year (with The Royle Family a close second).
For all that, the overall reputation of the genre rests somewhere down near General Pinochet's. The viewing figures are unequivocal: people love watching sitcoms. But we are also quick to slag them off. It's a national sport. In embarking on her first ever sitcom, wasn't Wood in danger of guilt by association? "I was worried about being tarred with that brush," she concedes. "Sitcom is such a horrible phrase now. It's almost synonymous with crap. But that's not my fault. One of my whinges is: why aren't there more good sitcoms? Often writers are constructing a group of people who don't have any reality. They're writing without passion. They think, 'Oh, we've got half an hour empty, let's bung together some people in an office or on a sofa.' Those shows never say anything. You have to really want to write a sitcom and have something to say that can only be said in that form."
So just what is Wood trying to say with Dinnerladies? "I wanted to introduce some new people into television. Good sitcoms, like Absolutely Fabulous or The Royle Family, show you a world that you didn't previously know existed."
It is true that, outside the world of soaps, women of a certain age are usually a blind spot for channel controllers. Dinnerladies - highlighting the casual profundity that often courses through banal-sounding female conversations - goes some way towards taking off their blinkers. Indeed, Dinnerladies is notable for being as much tragicomedy as sitcom. Wood cleverly peels back these women's lives and allows us a peek at the darkness visible within them. Jean's husband, we learn, "has given up in the duvet department," while Anita (Shobna Gulati) runs from the room weeping at the very mention of the word "babies".
Wood argues that pathos is an important aspect of comedy. "It just removes it from Sitcomland and roots it in a world I know. Most interesting things - whether they're drama or comedy - contain both elements. The best drama has always got funny bits in it, and the best sitcoms have a truth and, if not pathos, then something underneath that isn't just happy and jolly. Otherwise, it's meaningless, a fantasy. I can't watch farce because I can't believe anyone would behave like that. But if you look at something like Dad's Army, it's plausible. You know that Captain Mainwaring is jealous of Sergeant Wilson because Wilson is posher."
Mention of Dad's Army, perhaps the most celebrated Britcom, prompts the question: is there a magic formula? Wood reckons not. In this she echoes Dennis Main Wilson, the legendary producer of The Goon Show and Till Death Us Do Part, who once declared: "the basic rule of comedy is that there are no rules." Rather prosaically, Wood ascribes the success of a sitcom to hard work. She laboured for more than a year on the six half-hours of Dinnerladies, jettisoning three entire episodes and often working through the night on re-writes. She found the discipline so tough that she now admits she almost quit after four months.
A constant refrain - chorused in pontificators' columns - is that "they don't make sitcoms like they used to." Wood wishes to kill off that canard. "It's not any worse now. There have always been a whole load of diabolical sitcoms. We only remember the good ones. If you looked at the Radio Times from twenty years ago, you'd see a lot of horrors with John Alderton and Hannah Gordon and various people we've consigned to the waste bin of memory."
Like another great British comic tradition, the panto, the sitcom depends on easily identifiable figures whom we can drop in on unannounced at any moment and still recognise. They are often defined by a catchphrase such as "don't panic" or "stupid boy". We revel in that safe, snug feeling of familiarity - what else can explain the fact that Last of the Summer Wine is the world's longest-running sitcom?
Dinnerladies fits into that pattern; the strength of Wood's characters is that within the first five minutes we feel we know them. We've all met a Stan (Duncan Preston), the terminally dull handyman. "You can't shock me," he boasts. "I was once employed in the biggest brothel in Haslingden". "Doing what?" asks Bren (Wood). "Rewiring".
Equally, everyone is acquainted with a Tony (Andrew Dunn), the larky, laddish manager who sees innuendo in everything and has a soft spot for Bren. Wood characterises Bren and Tony's would-be romance as "very half- hearted, blundering, hopeless and British" - a neat summary of all her characters.
But how does Wood, a TV star of some 25 years' standing, remain tuned- in to the idiosyncrasies of people from whom she is now far-removed? "I pay little people to come round to my house and tell me about their lives," she laughs. "I talk like that myself, and I keep my ears open. I want my characters to sound realistic and not talk in, inverted-commas, jokey dialogue. I'm a lower middle-class person. I haven't altered my attitude - I've just added a few cars and houses. Alan Bennett has lived in Regents Park for 30 years, and he can still do it."
In Best of British, the BBC1 profile of Wood broadcast last week, Clive James remarked that "she's the woman you'd least like to have behind you in the queue in the supermarket when you're checking out because she'd be noticing everything in your shopping-trolley and reading your character from it."
Despite - or perhaps because of - her success, Wood has had her critics. "Journalists accuse me of being cosy," she says, "but I'm not worried about labels. It's something to do with being northern and having big bosoms. There's this association with baps and tea towels. But I don't just talk about gypsy creams. Someone said to me, 'well, you're not very political' - and that was supposed to be a criticism. But it was a compliment as far as I was concerned. Political comedy was just a fashion."
Wood's one concern is that she may be overdue for a backlash with this new venture. "It would worry me if the critics just decided it was my turn to get chopped, she said. "After all, I'm not setting myself up as the saviour of the sitcom. I just wrote it as a way of getting out of the house."