I'd like to try some alternatives to flour. For a biscuit recipe (Anzacs), I want to substitute almond meal for the plain flour the recipe requires. Should I still use bicarbonate of soda to get them to rise, or does this only work with flour?
We would caution slightly at trying to use all almond meal (ground almonds) as a substitute for flour in a recipe. Firstly almond meal doesn't contain any gluten and gluten is the stretchy protein in flour that helps to bind items like cookies together. As Anzacs usually contain whole oats and desiccated (dried shredded) coconut they are already quite crumbly and you may find that the almonds make the cookies slighty difficult to handle when cooked.
Also almond meal is quite moist, due to the oil in the almonds, so you may also find that the biscuits become slightly greasy as the ratio of fat to dry ingredients will be higer when using almond meal.
You can use bicarbonate of soda (baking soda) to help the biscuits rise and it will work to an extent with other ingredients but bear in mind that cookes tend not to rise much anyway.
We would suggest only substituting a small proportion of flour with almond meal. If you wish to avoid flour because of an intolerance to wheat then you could look at using one of the wheat free flour mixtures that are now available instead of regular plain (all-purpose) flour. These usually contain a mixture of alternative flours such as potato flour and rice flour and sometimes a natural subtance called xanthan gum which helps to mimic the action of gluten to bind the cake or cookie together better. In the UK Dove's Farm make a gluten free plain flour mixture and in the US Bob's Red Mill produce a gluten free all purpose flour mix. Note that oats contain gluten so the cookies won't be gluten free even if you use one of these gluten free flours.