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Hi. I have searched these forums trying to find a definitive quantity of ascorbic acid to be added to a cure dry cure bacon mix per kg meat. I have found .55g 550ppm for a kg of meat. Is this correct? Thanks

Don't use it myself, but Wheels' recipe calls for 0.45g per kilo of meat in his calculators - here's a link to his blog.
It's mentioned in the comments -
http://www.localfoodheroes.co.uk/?e=561

HTH.

As to whether ascorbic acid is a sensible ingredient to use is maybe for another topic; it's certainly used commercially in the UK, although not in the USA in bacon. It's worth noting that the FAO say:

http://www.fao.org/docrep/010/ai407e/ai407e14.htm wrote:In combination with the dry curing salt, also spices and sugars for flavouring and sodium ascorbate for enhancement of a typical curing colour (pickling-red) are used simultaneously. The use of ascorbic acid (instead of sodium ascorbate) in curing mixes and/or brines is discouraged as it could lead to a violent chemical reaction with the nitrite, especially when dissolved in water together with nitrite. The result would be fast nitrite breakdown and loss of its functional property.

So if you use it, don't premix and store the cure.

I've never seen figures specifying usage amounts for ascorbic acid in any of the regs - there may be some, but I've not seen them. There's a 500mg/kg max for sodium erythorbate, another Vit C salt, and if I recall correctly, someone worked out that about 450mg/kg would be the same amount of ascorbic acid, based on their respective molecular weights (or something similar).

This figure is supported by the US max of 469PPM (mg/kg) in cured products (although they specifically state the use of sodium ascorbate/erythorbate where it's required in bacon).

Hope this helps.

Phil