I realise that there are similar questions but I'm confused by the quantity I should use.
Various cooking websites say anything from equal quantities to 8 of gelatine = 1 of agar-agar.
Maybe the ones who say 1:1 haven't heated the agar-agar to near boiling point so it isn't fully dissolved whilst the 8:1 sites have boiled it in some liquid for 4-5 minutes, but this is unclear.
My current recipe uses about 6 leaves of gelatine or about 1tsp of gelatine powder.
Being a lemon cheesecake it also contains the juice of 3 lemons. Some sites say that acid can reduce the effectiveness of agar-agar.
Any advice would be appreciated.
Since posting the original question earlier today I have experimented with using 1 tsp agar-agar and it seems to work. I have been requested in one answer to post the whole recipe. Here it is in both gelatine and agar-agar forms.
Lemon Cheesecake
300 gr biscuits
75 gr melted butter
2 X 340 gr tubs (family sized) ordinary Philadelphia cream cheese
1 250 gr tub Mascarpone
Zest and juice of 2 lemons (maybe 3?)
100 gr caster sugar
6 leaves of gelatine (or one sachet of powdered - possibly only ½ is enough)
OR 1 level tsp agar-agar powder
Put the semi-sweet biscuits. 200gr digestive + 100gr other Hobnobs, almond biscuits,
ginger nuts etc. (or it could be all digestives) in a food processor and blitz
to a fine crumb. Add melted butter, blitz, scrape down, blitz again until
it's fully mixed.
Take a 24cm loose bottomed (springform) cake tin, use the loose bottom
as a template to cut a circle of greaseproof paper / cooking parchment
and assemble with the disk in the bottom. Add the biscuit mixture and press down
into an even layer. Use whatever you like, finger tips, knuckles, spoon, bottom
of a jar or glass. Put it in the fridge to firm up.
If using gelatine, separate the gelatine leaves and put them in a bowl of cold
water to soak. Not necessary if using powdered gelatine or agar-agar.
Put the cream cheese and Mascarpone in your food mixer and beat at high speed
for about 2 minutes, speed consistent with keeping the cheese in the bowl ?.
Scrape down the bowl. Beat in the sugar and lemon zest.
Squeeze as much water as possible from the gelatine leaves and add to the lemon
juice in a small bowl, or just stir in the powdered gelatine, making sure there
are no lumps. Add 1 or 2 tbsp of water (not too much, just enough to partly cover
the gelatine). Microwave at full power for 30 sec or until the gelatine has fully
melted when stirred into the liquid.
OR
Put the lemon juice + 1 or 2 tbsp water in a small glass bowl and whisk in the
agar-agar powder with a fork. Bring to the boil in the microwave, 1 minute at
full power then, stirring occasionally, run at low power for another 3 minutes
to keep it boiling.Check you don’t boil dry! Add more water if necessary.
Stop the mixer, add the gelatine / agar-agar / lemon juice scraping the bowl
to get it all. Cautiously restart the mixer. The contents will now be a lot more
liquid you won’t be able to run at full speed without it sloping all over the place!
When fully incorporated, pour the mix into the now chilled cake tin.
Scrape the bowl, shake the tin to get the top flat.
Put it back in the fridge for 2-3 hours.
With agar-agar the mixture will set much more quickly even at room temperature,
you need to work quickly.
Best Answer
Whole recipe would be useful.
Going by various popular vegan no-bake cheesecake recipes, I see 1 to 3 tsp of agar powder. Higher ratios of fat will need the higher amount of agar.
Lemon juice as a flavoring in this case shouldn't be an issue. Even half of the liquid being lemon sets up fine as in these bars: https://thehiddenveggies.com/vegan-lemon-bars/
Personally, I prefer kappa carrageenan over agar in stove top dishes as there is less boil time and partially sets while hot allowing for last minute tweaking. ie test amount removed to cool surface.