Apparently this type of biscuit was first developed by two Scots doctors in the early 19th century who believed the bicarbonate of soda was the digestive aid. These days, however, we’re more likely to look to the bran, from wholemeal wheat flour, and the oatmeal, for the more healthful qualities of digestives.
This is another one of my recipes from my old notebooks from when I lived at Old Man Mountain, New Zealand, in 1994-95, from my friend Nadia. I’ve no idea where she got the recipe from. If memory serves, it was in one of her notepads. All I know is we were making a baked cheesecake, needed some digestives, and this was a better option than driving 15km to a shop.
This time round I’m making them because I want to try this amazing looking, amazingly indulgent recipe from Kate “The Little Loaf” Doran. Kate has her own, similar recipe, for digestives, but well, I wanted to use mine, another memory of Nadia.
A bit of chemistry
This is a slightly tweaked version of the one I’ve got in my notepad. That one used baking soda, aka bicarbonate of soda aka sodium hydrogen carbonate, for a little bit of raising agent. The thing about baking soda, though, is that it’s an alkali and it needs an acid to react with to create the carbon dioxide that gives lift. That’s why US muffin recipes, say, often include yogurt, for the lactic acid. Other recipes might use citrus juice, milk or even vinegar. But my old digestive recipe had nothing acid in it*. So I’ve replaced the baking soda with baking powder. And what is baking powder? It’s pre-mixed combo of baking soda and something acid for it to react with when you combine and bake. In this case, sodium phosphates: that is, sodium salts of phosphoric acid.
A word on the oatmeal: you can use whatever you fancy, though fine or medium are probably best. I didn’t have any, so I just used some porridge oats, which I whizzed in a food processor – to make a medium-coarse meal. Hence the results in this case are especially rustic.
Makes about 30 biscuits
150g unsalted butter
250g wholemeal flour (plain/low protein)
250g oatmeal (fine or medium)
80g light soft brown sugar
1/4 tsp salt
1/2 tsp BP
2 eggs, beaten (approx 120g beaten egg)
1. Preheat oven to 200C.
2. Combine the flour, oatmeal, salt and baking powder in a bowl.
3. Rub the butter into the flour mix until it resembles crumbs.
4. Stir in the sugar.
5. Bind with the beaten egg, to form a rough dough. Don’t overwork it, or you’ll toughen it up. You can wrap it in plastic and give it a rest in the fridge at this point, but I can’t say I noticed the difference.
7. Cut circles of about 70mm diameter. It doesn’t matter too much if you don’t have this size cutter; you could even just use a glass. Bring together any scraps, roll and cut circles to use it all up.
They’re excellent with cheese, dunked in hot chocolate, or used for a cheesecake base.
* Food charts seem to vary in terms of whether whole chicken egg is acid or alkaline. Some list them as acidic, but egginfo.co.uk says, “The pH of the white and yolk are different and change differently during storage. The initial pH of yolk is slightly acidic (reported values range from 5.9 to 6.2) and rises slightly during storage to about 6.8. Egg white pH is initially in the region 7.6 and rises to 8.9 -9.4 after storage due to CO2 loss through the shell. The natural ratio of egg white to egg yolk in an egg is 2:1 and therefore when mixed together liquid whole egg has a pH range of 7.2 to 7.9.” (If you can’t remember school science, low pH is more acidic, high pH is more alkaline. The mid-point, neutral, is 7pH, the pH of pure water.)