Ginger Beer, done, stuck or not gonna go?

Hi guys,

I threw together a batch of ginger beer 7 days ago using the following:
3kg Raw sugar
2 Lemons (juice and rind)
Lightly boiled a kilo of ginger for 2 hours, sieved.
5g vegemite (a spread that consists mainly of yeast extract and malt extract, often used around australia and NZ in peitre dishes for growing bacteria/fungi, figured it would be a good nutrient).
and some spices, mainly cinnamon.
23L water

A packet of Safale s-04, started at about 23C, has been kept around 18-20 since then.

So my problem is this:
Initial G: 1.050
Day 3 SG: 1.042
Current SG: 1.040
Expected FG: 1.010

I'm not sure whether it is stuck (in which case I would just throw in more yeast), finished fermenting (which seems unlikely, but I am a little thrown off by having no malt in there), or out of nutrients (which again would be due to the lack of malt, but I tried to counter this by using raw sugar and the vegemite).
In the last day or so a small krasen has formed, but it does not appear to be accompanied by any actual fermentation.

Please help.

Since the gravity is moving, albeit slowly, I think it's clear that it is in fact fermenting and not stuck. My guess is the Vegemite may have been a much poorer nutrient than you'd hoped (doesn't Vegemite have a lot of salt in it too?) - or perhaps you just didn't add enough of it to make up for the deficiencies of your must. You won't get much in the way of a Kraeusen without malt - kraeusen comes primarily from proteins, of which you have almost none.

I'd try adding some yeast nutrient. If you don't have access to commercial yeast nutrient, at least go to the pharmacy ("chemist" in NZ?) and get some zinc supplement tablets. Boil one of those in water for 10 minutes (to sanitize) and add the water to your ale. Jamil and others often talk about how important zinc is to yeast health.