Sous Vide Asparagus: Temperature and Time

Sous vide asparagus cooks at 183°F (83.9°C) for 10 to 30 minutes. Thin spears are done at the short end of that range and thick spears need the long end. The result is bright green and tender with a little snap.

Temperature and time for asparagus

The calculator has one setting for asparagus.

The minimum is 10 minutes and the best window is 10 to 30 minutes. The time is for whole spears. Thickness is not an input for asparagus in the calculator, so you place your spears within the window by their size.

The calculator sets no maximum for asparagus. Its note is that the upper time is a texture guide, not a limit, and that longer cooking only makes the food softer.

This is a short cook for a vegetable. Carrots use the same bath temperature and take 45 minutes to 1 hour, corn on the cob takes 30 to 45 minutes, and the vegetables chart covers the other vegetables in the calculator.

Why the bath is hotter than for meat or fish

Douglas Baldwin's guide to sous vide cooking states that most vegetables need much higher temperatures than meat and must be cooked separately. Meat temperatures are too low to soften plant cell walls.

Anova's vegetable guide describes pectin as the glue that holds plant cells together and says it does not break down until 183°F (83.9°C).

Asparagus therefore cannot share a bath with salmon or any other fish or meat. Plan for two baths, or cook the asparagus another way when the circulator is in use.

Thin or thick spears

The calculator's note is that thin spears are done at the short end of the range and thick spears need the long end. Heat reaches the center of a thin spear sooner, so it softens sooner.

America's Test Kitchen's sous vide asparagus recipe is specific about size. It calls for thick spears, 1/2 to 3/4 in (1.3 to 1.9 cm) in diameter, and says not to use pencil-thin asparagus because it overcooks too easily. Its bath is 180°F (82.2°C) for 20 minutes, a little cooler than the calculator's setting.

The size advice leads to two rules:

• Sort before you bag. Put thin and thick spears in separate bags so each bag can come out at its own time.
• Take thin spears out near 10 minutes. The long end of the window, up to 30 minutes, is for thick spears.

Keeping the color

The University of Illinois Extension's handout on cooking vegetables explains the color change in green vegetables. Acids and prolonged heat turn chlorophyll into pheophytin, which it describes as "a drab olive green." It names lemon juice and vinegar as acids that destroy chlorophyll, and it advises cooking vegetables as quickly as possible.

Both causes are under your control in a sous vide bag.

Time. The 30 minute end of the window is not a limit in the calculator, but prolonged heat is one of the two causes of the color change, and longer cooking makes the spears softer. Stay inside the 10 to 30 minute window, and open the bag when the time is up. A sealed bag that sits on the counter stays hot, and the asparagus keeps cooking inside it.

Acid. Keep lemon juice and vinegar out of the bag. Add them at the table or just before serving.

America's Test Kitchen does not recommend making its sous vide asparagus in advance.

How to sous vide asparagus

1. Heat the bath. Set the circulator to 183°F (83.9°C).
2. Trim the spears. America's Test Kitchen's guide to cooking asparagus cuts off the bottom 1 in (2.5 cm) and peels the lower half of each spear. It reports that snapping the ends by hand can remove up to 50 percent of the weight, while trimming and peeling keeps the loss under 30 percent.
3. Sort by thickness. Thin spears in one bag, thick spears in another.
4. Bag in a single layer. Add salt and a little butter or oil. Anova's guide says fat in the bag helps fat-soluble flavors from any herbs or aromatics move into the vegetables.
5. Seal. America's Test Kitchen double bags in zipper-lock freezer bags to guard against a seam failing, and Anova's guide warns that zipper seals can break at high temperatures. A vacuum sealer also works, and the water displacement method removes the air from a zipper-lock bag.
6. Submerge and weigh down. America's Test Kitchen weights the bag so the spears stay fully under water and cook evenly.
7. Cook for 10 to 30 minutes. Thin spears at the short end, thick spears at the long end.
8. Serve. Open the bag as soon as the time is up. Season, and add any lemon juice now.

For browning, Anova's guide gives a grill finish of 45 seconds to 1 minute per side over high heat on clean, oiled grates.

Cooking asparagus from frozen

The calculator's asparagus times are for spears that are not frozen. Its instruction is to thaw them first, then cook for the normal 10 to 30 minutes.

The guide to cooking from frozen covers the foods that can go straight from the freezer into the bath.

Safety

The calculator lists no safety warnings for asparagus. It does not apply a pasteurization table to it, and it shows the pasteurization status as not applicable.

Submersion still matters. Baldwin's guide says pouches must be completely submerged and not tightly arranged or overlapping, to prevent undercooking. The broader rules are in is sous vide safe.

Common problems

The bag floats. Baldwin notes that at high bath temperatures some of the liquid in the bag turns to vapor, so the bag puffs and may rise. He holds bags under with a wire rack. Anova's guide suggests a weight inside the bag or clipped to the outside, and Jason Logsdon's vegetable guide suggests a plate or a lid on top.

The spears turned olive green. The cook ran long, the bag sat sealed after the bath, or there was acid in the bag.

Some spears are soft and some are firm. Thin and thick spears shared a bag. Sort by size and give the thin ones less time.

The bottoms are stringy. The lower stalk has a fibrous exterior. Peel the lower half before bagging, as America's Test Kitchen does.