I have made Nigella's Redcurrant Slush sorbet, but as it churned in the ice cream machine it became almost foamy, doubled in volume and it turned out light pink in colour. Also after 3 nights in the freezer it was still very soft and did not harden at all. I skipped the Cointreau (so I could not blame the alcohol for the softness) and I use a Gaggia ice cream machine. Why does this happen and what can I do to prevent it? I would really like to have a bright red sorbet.
Nigella's Redcurrant Slush Sorbet is intended to be slightly slushy, and not quite as firm as a more traditional sorbet, so will always be slightly soft, even after a couple of days in the freezer. Alcohol will be one of the ingredients that causes this softness, though it will also help to prevent large ice cryatals from forming. However, the quantity of sugar in the recipe will also deternine how soft it is and for a firmer sorbet you may need to reduce the quantity of sugar slightly. However bear in mind that when frozen the mixture will taste less sweet so if you do reduce the sugar make sure that you taste the mixture before churning it and make sure it is not too tart.
Ice cream machines contain a large paddle which turns as the mixture freezes, churning the ice cream or sorbet. This churning process incorporates air into the mixture. This increases the volume and will also make the mixture turn slightly paler in colour. The recipe refers to the sorbet as being "puce" in colour, rather than vibrant red. If the redcurrants used were slightly pale in colour then this means the resulting sorbet will be paler in colour. You could also try chilling the sorbet mixture before churning it. If the mixture is cold before it goes into the ice cream machine then it will freeze more quickly and will be churned less, helping to reduce the volume slightly and hopefully preserving a bit more of the colour.
if you have an ice cream maker that requires the bowl to be chilled in the freezer before using then we would recommend that the mixture is chilled before churning.
A link to the recipe is below.