Ask Peter: Gelatine
I am very confused about gelatine — many recipes use the sheet variety now but seem very loose on the amount, one sheet seems to do it all, whereas the powdered variety is measured out carefully. Is it true that the sheets are superior to the powder? I avoid making anything using gelatine as I think I am going to muck it up by buying/using the wrong thing. Abby
I wish I had a foolproof answer for you. When I first began using sheet, or leaf, gelatine in the late 80s I felt one of the culinary world’s hassles was forever answered. Dissolving powdered gelatine had always been slightly tricky as I could never seem to get 100 per cent of the granules into the liquid I was trying to set — there would always be a few slightly undissolved ones stuck to the dish I’d soaked them in. It wasn’t in reality a huge problem but it caused me a few moments anguish from time to time.
Then on the scene appeared the miracle answer — sheets that you simply soaked in ice cold water for five minutes, before gently squeezing out the excess liquid and adding to a warmed liquid to dissolve them. For years it was a very simple equation of one sheet to set 100ml liquid. As to how many teaspoons set 100ml of liquid — I could never really figure it out.
Then one day I was talking to a friend, a keen home cook, and he said the panna cotta recipe I’d given him was too soft and he’d had to serve them in the mould rather than unmoulding. Shock horror! How could this be?
Well it turned out that the leaf gelatine he’d bought from the supermarket was quite different to the one we chefs were using in restaurant kitchens. They were thinner and smaller — which obviously meant one sheet was going to set much less liquid than mine. The more I looked into it the more complicated it became as not all gelatines are alike. Some will set a liquid much firmer than others, some will produce a more cloudy result than others, some need more soaking — or blooming, the term more often used for soaking gelatine. Writing cookbooks and knowing people around the world are feeling disappointed with the end result is also heartbreaking, as all my recipes work when made at home, which is where I always shoot them.
The scientific part of what constitutes “liquid” is also worth pointing out. For me the easiest way of describing this, which will affect how much gelatine you need for a recipe, is that water is 100 per cent pure liquid. There’s no solids or fats in water — just a few miniscule amounts of harmless chemicals like sodium, magnesium etc. Milk and cream (think panna cotta) are milk fats suspended in water — cream having more fat, and therefore less water — so it needs less gelatine to set it. With fruit juice, apple juice generally is very watery and is mostly water whereas tomato juice is much thicker, and like cream, has less water so needs less gelatine. The reason I’m pointing this out is that a fruit jelly made from fruit juice, or a panna cotta or bavaroise made from cream and milk, can vary enormously in how much gelatine is needed, with skim/trim milk needing more to set it than regular milk.
As to how much powdered gelatine is the equivalent to leaf gelatine — there is no simple answer as there are several quite differing varieties on the market.
If you have a set of those very precise scales that coffee buffs seem to use these days when making the "perfect espresso”, that can help. Generally, 7g of gelatine will set 500ml liquid; 7g of powdered gelatine is around 2½ teaspoons.
With leaf gelatine — you’re best to only buy packets that instruct you clearly what they will set and then adjust your quantity accordingly. And then keep a record of what you used and use this as your “go-to” referral every time.
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 here.