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Low-Carb Black Widow Cocktail

4.2 stars, average of 84 ratings

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This spooky low-carb cocktail is perfect for Halloween! I used homemade blackberry-lime syrup and substituted the commonly used simple syrup with powdered Erythritol. There are other options you can try:

  • Skip the powdered sweetener in the blackberry juice and make your own simple syrup like in this Spicy Low-Carb Margarita. The only drawback of making simple syrup this way is that it may partially crystallise once it's chilled.
  • You could use NuNaturals Simple Syrup. Apart from plain simple syrup, it's available in several different flavours such as Ginger Syrup which worked wonderfully in my Keto Ginger & Rhubarb Creamsicles. Just remember to use the recommended amount as too much would make your cocktail way too sweet.
  • Lastly, you can just use a few drops of stevia. NuNaturals are my favourite as they don't taste bitter.

Note that this recipe makes about 2 1/4 cups (530 ml/ 18 fl oz) blackberry juice. This will be enough for 6 cocktails. Fibre is counted partially (25%) as most of the pulp and seeds are discarded.

Looking for a spooky treat? Try my Halloween Keto Pizza, Spooky Eyeball Cookies, Cheesy Keto Spinach Crackers, and even more Halloween Keto Recipes.

Hands-on Overall

Serving size cocktail

Allergy information for Low-Carb Black Widow Cocktail

✔  Gluten free
✔  Dairy free
✔  Egg free
✔  Nut free
✔  Nightshade free
✔  Pork free
✔  Avocado free
✔  Coconut free
✔  Fish free
✔  Shellfish free
✔  Beef free

Nutritional values (per serving, cocktail)

Net carbs4.7 grams
Protein1.1 grams
Fat0.4 grams
Calories166 kcal
Calories from carbs 71%, protein 16%, fat 13%
Total carbs5.7 gramsFiber1 gramsSugars0 gramsSaturated fat0 gramsSodium8 mg(0% RDA)Magnesium17 mg(4% RDA)Potassium135 mg(7% EMR)

Ingredients (makes 1 cocktail)

Homemade blackberry syrup:
  • 450 g fresh or frozen blackberries (1 lb)
  • 1/4 cup lime or lemon juice (1-2 pieces)
  • 1 cup water (240 ml/ 8 fl oz)
  • 1/2 cup powdered Erythritol or Swerve (80 g/ 2.8 oz)
Each Cocktail:
  • 90 ml homemade blackberry juice (3 fl oz)
  • 1/4 cup vodka (60 ml/ 2 fl oz)
  • ice
  • Optional: sparkling water (soda water) to top up
  • Optional: acai powder or freeze-dried berry powder mixed with granulated Erythritol, and fresh blackberries for decoration


  1. Place the blackberries in a saucepan. Low-Carb Black Widow Cocktail
  2. Add the lime juice and water. Bring to a boil over a medium heat. Boil for 3-5 minutes. Low-Carb Black Widow Cocktail
  3. Once softened, mash the blackberries using a fork.
  4. Pour through a fine mesh sieve and using a spoon, press the blackberries through so that only the skins and seeds remain in the sieve. Low-Carb Black Widow Cocktail
  5. Pour into a jar. The juice should be quite thick, almost the consistency of syrup.
    Note: this recipe makes about 2 1/4 cups (530 ml/ 18 fl oz) blackberry juice. This will be enough for 6 cocktails. Low-Carb Black Widow Cocktail
  6. Add the powdered Erythritol and mix until combined. Let it cool and refrigerate until ready. The juice will keep refrigerated for up to 5 days. Low-Carb Black Widow Cocktail
  7. To serve, optionally decorate your cocktail glasses by dipping the rims in water and then in a mixture of acai powder (or any berry powder). Fill each glass with ice and pour in the vodka. Low-Carb Black Widow Cocktail
  8. Add the sweetened blackberry juice. Low-Carb Black Widow Cocktail
  9. Decorate with more fresh blackberries or mint leaves and serve. Low-Carb Black Widow Cocktail

Ingredient nutritional breakdown (per serving, cocktail)

Net carbsProteinFatCalories
Homemade Blackberry Juice (KetoDiet blog)
4.7 g1.1 g0.4 g38 kcal
Vodka, distilled alcoholic beverage (~40% vol)
0 g0 g0 g128 kcal
Ice cubes
0 g0 g0 g0 kcal
Total per serving, cocktail
4.7 g1.1 g0.4 g166 kcal

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Martina Slajerova
Creator of

Martina Slajerova

I changed the way I ate in 2011, when I was diagnosed with Hashimoto’s, an autoimmune disease that affects the thyroid. I had no energy, and I found it more and more difficult to maintain a healthy weight.

That’s when I decided to quit sugar, grains, and processed foods, and to start following a whole-foods-based ketogenic approach to food.

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