I must admit to a certain amount of fascination for the intricaces of the science of cooking: precise measurements (metric, of course), the chemistry of mixing different ingredients, reactions to specific catylists such as heating or freezing. Indeed, the pages of my copy of Harold Magee’s On Food And Cooking: The Science And Lore Of The Kitchen are very well worn (in several editions over the years). But, when it comes down to actually operating in the kitchen, I always opt for the ad-lib mode where there is more sponteneity than precision, usually cooking with what I have on hand. It would seem that, in practise, it is more of an art than a science.
Yet, one of the things I’ve learned is that you cannot have one without the other. In other words, if you know how things work in the kitchen “laboratory”, it is easier to give full reign to your creative streak, knowing what will work and what won’t. It also allows you to experiment to see the flavour and texture permutations, and learn from both your failures and sucesses. That pertains to such things as my earlier, somewhat feeble, explorations into the art and science of cheese making and more recently my search for creative uses of sourdough starters.
With that little philosophical thought in mind, lately (now that the weather is warming) I’ve been experimenting with gelato making – much to the delight of my test subjects (AKA family and friends). Now this certainly involves a lot of science. The primary aim in making ice creams, gelato, sorbets and various other iced desserts is to create a smooth frozen product with the smallest possible ice and sugar crystal formation. The main way that this is achieved, other than adding tiny air pockets in the churning process, is through the type of sugar used and thickening agents known as stabalisers (see the note below on types of sugars). Then there are the optional inclusions of small amounts of alcohol with their higher freezing points that also inhibit crystal formation. Of course, ice creams and, to a certain extent, gelatos are also helped by the fact that they contain dairy solids and fats, replacing some of the water content. Sorbets (sometimes called sherbets in the US) are a different – much more complex – story which I have yet to tackle, but has been handled quite effectively by Sandra @ Please Pass the Recipe in her post on chocolate sorbet.
After quite a bit of experimentation and reading up on the topic, I have come to the conclusion that – like most recipes – it is a matter of balance of ingredients. The science is in understanding the proportions and properties of those ingredients, and the art lies in the choices made – usually pertaining to taste and texture – when mixing them together. In the case of ice creams and gelato, that means a balance of sugars, fat, starch and potentially alcohol in order to achieve a smooth (non-crystaline) texture. Also, I firmly believe that, in creating gelatos, it is possible to use ingredients easily obtainable in my kitchen and pantry cupboards. No special ingredients required.
Sicilian Gelato Base
After all that reading and experimenting, I’ve opted for a Sicilian style gelato that is based on a sweet, starch-thickened dairy custard. Flavourings in the form of fruit pulps, chopped nuts, cocoa, vanilla, etc. are later added along with 60ml to 90ml gloucose-rich syrup (see note below) and, optionally, a small amount of alcohol (up to 60ml). I’ll be giving examples of this in other posts on flavoured Sicilian gelatos. For now, I’d simply like to explain the ingredients in the base mixture.
1. The Dairy Element
Most gelatos are made with milk, not cream. However, if you want a richer – almost ice cream-like – smoothness, substitute a portion of the milk for cream. Note, anything beyond 200ml of cream for most combinations becomes too cloying, but that is just my personal taste. I also tend to use semi-skim milk, so the inclusion of cream bumps that fat content up. If using whole milk, you may want to consider reducing the amount of cream or eliminating it altogether. It is also best to pair the creaminess with the other added ingredients – consistency as well as flavour.
- With 200 to 300ml fruit pulp:
500ml milk or a percentage of milk and cream
- Other flavors that don’t involve a bulk of fruit:
700ml milk or a percentage of milk and cream
2. The Custard Sweetener
Since the high glucose syrup will be added with the additional flavours, sugar (sucrose) is added here. Of course, the dissolving and heating of the sugar in the dairy liquid breaks down the sugar crystals. Also, the milk/cream fats and the starches interfere with the sugar’s ability to reform into crystals when the mixture cools.
- 100g caster sugar
3. The Starch Thickener
The amount of corn flour also depends on the consistency of fruit pulp to be added. The thicker the pulp, less corn flour is required. The blog Ice Cream Nation has a good explanation of the uses of starch in gelato making. It also acts as a stabaliser, ensuring the gelato remains creamy once frozen.
- 24 to 36g corn flour (or other starch such as potato starch, arrowroot, etc.)
4. The Procedure
Mix the corn flour with a little of the milk. Put cream (if using), the remainder of the milk and sugar in a pot on medium heat. Stir in the cornflour milk and stir well to make sure that there are no lumps. Cook until it begins to thicken, then stir continually until it has the consistency of thick custard – just as it begins to bubble. Remove from heat and let it cool, stirring it periodically to prevent a skin forming on top. Then add the flavour ingredients and process in an ice cream machine.
Sugar is sugar, one would think. However, there are many different sorts and I’m not talking about white, brown, or demarara sorts. You can usually spot these different sugars by their –ose suffix, like sucrose, glucose, dextrose, fructose…. First, normal table sugar is in fact soucrose, a highly crystalised form of sugar. Gloucose, in particular, but to a certain extent fructose (which occurs naturally in fruit), are less likely to form crystals and are therefore ideal sweeteners for ice creams. Also, heat will alter sucrose, a process that can be seen in jam making.
Some common natural sugar syrups: (% fructose/gloucose content):
- honey (40/30)
- golden syrup (50/50)
- corn syrup (variable, but mostly glucose)
- high fructose corn syrup (53/42)
For more on the science of ice cream making, see Homemade Ice Cream @ Science and Food blog, straight from the science labs at UCLA.