Oh how simple my world must have been.
If I've understood it correctly, and it's entirely probable I haven't, you slash your bread so that it can rise to maximum height without exploding. This is because the heat of the oven causes something caused "oven spring"- that final push upwards. Because the bread has a certain surface tension, you want the bread to rise as much as possible before the crust bakes hard and doesn't allow any further growth. So in this respect slashing helps, (but so does causing a moist environment in the oven - steam. More on this another time).
If you slash, you control where the bread expands. If you didn't and it needed to expand, it might burst in an uncontrollable fashion. So slashing can be decorative and serves a purpose. Btw, you only really need to slash with certain types of bread. Some bread that don't rise much, such as a pure rye, don't need slashes.
But how to slash?
People are nervous of slashing the dough, with good reason. You've spent the best part of a day making your sourdough baby and when you tip it out on a (preferably pre-heated) tray or stone you don't want to muck about with it anymore than you have to. Slashing takes a bit of confidence and good slashing also depends on the proving. If you've overproved, slashing is more likely to make your bread deflate, for instance.
When I first started slashing I used a really sharp knife. I found this dragged and it made me panic, because the bread seemed to deflate (although it seemed to recover fine in the oven).
I never need a reason to buy a new gadget or a specialist tool so I looked up what you could use.
- A razor blade - no good for me as I have young children and I wasn't going to risk a naked blade escaping from the drawer.
- A grignette or lame - a posh Stanley knife.
Naturally, I decided, I needed one of the latter.
You can get ones with rotating blades (so you can use both sides, although there's nothing to stop you swopping hands and doing it but I guess that requires some dexterity), ceramic blades, steel blades, replaceable blades. They are used "by the professionals".
I got this one:
Mure and Peynot Panette Professional Grignette, £9.99, close up of curved blade
Same, seen side on and full length and with safety cover.
It has a replaceable blade and a safety cover as seen above.
Hugh Fearnley-Whittingstall, in his lovely little book on bread suggests you can use a bread knife. If you've ever tried to slice a tomato with a regular (even really sharp) knife and a serrated bread knife, you'll know the latter makes the job so much easier.
Surely a bread knife couldn't be as good as, or better, than a special tool?
Well actually yes it can. I'm sure if you're a proper artisan baker who makes all sorts of fancy patterns on their bread, then I'm sure that a grignette, in your hands does amazing things. But I can't get the slashes to go deep enough.
The bread knife does a far better job.
Slash made with grignette on potato bread. Nice, but see how shallow it is? Although you'll see the bread knife is already starting to muscle in.
This morning's bread, white sourdough, slashed with a simple bread knife. Better, no?
Yesterday's bread: three flour mill loaf, with bread knife slashes.
Conclusion: it may not be a wallet-busting exercise, buying a professional grignette, but I think a bread-knife does the job better. With the money you save you'd be better off buying a banneton, which is worth the money. But, more on this another time.