You’d think, having published my 12-step roastie program two years ago, followed by last year’s investigation of the best spud for the roastie job, that when this Christmas rolled around, I’d really have no more to say on the subject of roast potatoes for the big day. I might even have thought as much myself but, as it turns out, both you and I were wrong. I realised as much last Monday morning, as I was listening to the John Murray Show on RTE Radio One.
Brenda Costigan, longtime cookery writer, was a guest on the show and some listeners has asked for her tips on roast potatoes, as you do at this time of year. What followed was something I certainly didn’t expect, because she suggested that you could prepare your roasties ahead of time and freeze them.
The idea fairly stopped me in my tracks, because I’ve just never thought that a spell in the freezer did a cooked potato any favours. I somehow imagined that roasting a spud that had been previously frozen was a recipe for sogginess, but there was only one way to be sure – a taste-off between potatoes cooked, frozen and roasted the Brenda way and my own freshly prepared version. I donned my roastie lab coat and went, once again, into investigative action.
Brenda’s method for roast potatoes runs something like this:
- Boil or preferably steam your potatoes until just tender.
- Once cooked, spread them out on a tray, allowing them to cool more quickly.
- Coat each potato fully with melted butter (or your preferred cooking fat) and sprinkle with salt and pepper.
- This can be done a few hours before roasting or (what intrigued me more) she says that the potatoes can be frozen once cooled, and should be defrosted thoroughly before roasting in a hot oven.
- She notes that, between the initial cooking and subsequent roasting, that the potatoes may tend to blacken and suggests that this is less the case with organic varieties.
There was nothing else for it but to get in some Golden Wonders and Roosters and put Brenda’s method to the test. Once steamed, cooled and coated with butter, it was into the freezer with the spuds. I later defrosted them overnight in the fridge, thought some skeptical thoughts about how squidgy they felt, before cooking them at the same time as a freshly prepared and par-boiled batch of soon-to-be-roasties.
Side-by-side, the previously frozen spuds were definitely moister inside than the freshly roasted versions (though, to be fair, neither the Roosters nor the Golden Wonders were soggy to quite the extent I had anticipated). They showed a slightly greater tendency to stick to the roasting tray – also, I would expect, because of the additional moisture – while texture-wise and regardless of variety, there was a definite graininess in the potatoes that had been frozen.
The verdict? Truthfully, the roasties that had been frozen weren’t that bad, and it does occur to me that with so many other things on the Christmas dinner plate, and with enough gravy and bread sauce slathered over the spuds, that the difference in texture might be sufficiently masked. Personally, though, I would choose fresh roasties every time (and made with Golden Wonders please).
The After Thoughts
While practical experiments like this are one way of answering certain kitchen questions, I always like it better if I understand what’s really going on.
I had wondered, for one thing, about Brenda’s comment that organic varieties of potato would tend to blacken less after cooking. According to Harold McGee, renowned food scientist and author of McGee on Food & Cooking, the development of gray or blackish pigments in potatoes when left to sit after cooking is caused by a reaction of iron ions, phenolic compounds and oxygen. Shirley Corriher in Cookwise describes the same reaction and also notes that some varieties of potato may be more susceptible to this than others. I would guess, in that case, that the organic varieties that Brenda mentioned are less susceptible to this effect, though whether that is down to the specific variety or their organic cultivation is an open question. In any case, both Harold McGee and Shirley Corriher note that this blackening effect can be minimised in boiled potatoes by making the water distinctly acidic halfway through cooking e.g. by adding some lemon juice or cream of tartar. Coating the cooked potatoes with butter, as Brenda does, also seems to inhibit blackening and my guess is that this may be due to the presence of antioxidants in the butterfat.
As regards the freezing of cooked potatoes, the graininess which I could discern is no doubt due to the formation of large water crystals which rupture internal membranes within the potato. Commercially frozen potatoes are generally frozen rapidly and at a much lower temperature, forming smaller crystals, so there is less internal damage. Home frozen spuds, however, are not so lucky.
In general, and as you may have observed yourself, cooked potatoes can develop a stale flavour after a few days (or even after a few hours if kept hot for service). Harold McGee notes that aromatic compounds in the potato are temporarily stabilised by the potato’s antioxidant vitamin C, but with time, the vitamin C is used up and the compounds become oxidised, producing less pleasant aldehydes and that resulting cardboard-like taste. As my own experience confirms when it comes to spuds, fresh is always best.