Avoid a sticky situation
As a teacher of food technology, I appreciate the way you explain the scientific concepts underpinning your craft. I am hoping you can help me understand why some recipes specify not to stir a sugar solution.
Good old sugar - it's quite a special and complicated ingredient and depending on where you sit on the ingredient fence, it's either white death to be avoided or a thing to be used with gay abandon. I have to confess to having a sweet tooth so I am a fan, and my dentist may well be happy for the extra work he gets from me. But what you ask is more scientific than flavoursome.
Sugar is a type of carbohydrate which we generally buy only in its crystalline form. It is important to remember that it likes being a crystal, so it will do anything to revert back into that form. Thus the odd stray grain of sugar, no matter how small, can "seed" the syrup and start the fascinating process of recrystallisation.
The most common complaint is that just when you think you've made the perfect syrup or toffee, it will suddenly begin to turn from a pot of glossy syrup into a white, foamy, gritty syrup - or worse still, a lump of crystallised mess.
The rule of thumb when making sugar syrup (which can then be cooked into toffee at the other end of the spectrum) is to start with a completely clean pot - ideally heavy based, which will conduct heat better. Make sure you have a heat-proof, spotless (no grease or moisture) pastry brush and a metal stirring spoon, as wooden spoons are more absorbent and can harbour moisture or flavours, such as garlic from your last risotto.
Avoid at all costs getting sugar on the side of the pot, as these crystals will hang on there and then drop into the syrup, which can cause it to crystallise. Add half the water, gently tip the sugar into the centre of the pot, then slowly add the rest of the water. Slowly bring to the boil (notice all the "slowlies" here) and you can gently stir it before it boils to help dissolve the sugar. If you notice crystals have formed on the sides of the pot then dip your pastry brush into tepid water and brush these down into the not-yet-boiling syrup to dissolve them. Alternatively, put a lid on the pot for a few minutes and the steam will cause the crystals to drip down themselves.
Once the syrup comes to the boil, do not stir it, don't shake the pan, and keep the heat high and constant and cook to your desired degree. The risk of stirring is simply that there may be some undissolved sugar stuck to the spoon.
A sugar thermometer is fairly essential for making anything more than a basic sugar syrup and well worth the price. I always have a coffee mug of hot water to the side of my sugar cooking in which to dip the thermometer once cooled. The water will help dissolve the sugar stuck to the thermometer and make it easy to clean.
Having absorbed the above fool-proof method, when you become more confident, you can make toffee with no water at all. Simply heat up a heavy-based pan with cm layer of caster sugar and cook over medium heat, gently shaking the pan from time to time with the odd stir, until the sugar melts. Then turn the heat up and cook until golden. It's quicker than using a mixture of water and sugar as you don't need to evaporate the water, which is essential when making golden or dark toffee.
And last, to make these techniques even more foolproof, replace 30 per cent of the sugar with glucose syrup, or add a teaspoon of lemon juice per 200g caster sugar. Both help prevent crystallisation.
In our Ask Peter series, executive chef Peter Gordon answers your curly culinary questions. If you’re stumped over something food-related, send your question to firstname.lastname@example.org and keep checking in for answers. You can read more on Peter on his website, have a read of his Ask Peter articles or check out his recipes on our site.