When preparing potatoes for cooking, it’s common practice to place the peeled potatoes in ice water while you finish prepping the rest of the meal. But why exactly do people do this? What purpose does the ice water serve? There are actually a few good reasons for this simple kitchen step.
Prevents Browning
The main reason peeled potatoes are placed in ice water is to prevent them from turning brown. When a potato is peeled, enzymes called polyphenol oxidases are released and exposed to oxygen in the air. This causes a chemical reaction that produces melanin, which causes the discoloration or browning on the potato’s flesh.
The icy temperature of the water helps slow down this enzymatic process. The cold causes the enzymes to work more sluggishly. Putting the peeled potatoes in cold water buys you more time before they start to brown while you finish up other recipe steps.
Retains Moisture
Leaving peeled potatoes out in the open air can also cause them to dry out a bit. The cut surfaces will become dried and hardened. Plunging potatoes into water helps prevent this dehydration by surrounding them with moisture.
The chilled water is especially effective at keeping potatoes from losing moisture. The cold temperature makes it more difficult for the water to evaporate. So a chilled water bath provides a humid environment that maintains the potatoes’ moisture content.
Removes Surface Starch
Soaking potatoes in water can also help rinse off some of the excess surface starch. Raw potatoes contain starch granules that can make the peel and outer portion feel slightly slimy when cutting them. Letting peeled potatoes soak in water dissolves some of this free starch into the water.
This can help prevent the potatoes from sticking together when boiling them. The water bath creates less viscous, cleaner-feeling potato pieces by removing some surface starches.
Makes Them Easier to Handle
Chilling potatoes in ice water also firms them up slightly, which can make them easier to handle, cut, and work with. The cold causes the potato starches to congeal a bit. This makes the potato flesh feel less soft and slippery.
The firmer texture provides more friction when grasping the potatoes, making them easier to manage when cutting, dicing, or adding them to a dish. The water turgidity improves grip and reduces slipping when handling the peeled pieces.
Quick Summary
- Prevents browning – Slows enzyme reactions
- Retains moisture – Prevents dehydration
- Removes surface starch – Improves texture
- Firms up potatoes – Makes them easier to handle
The Science Behind Potato Browning
Now let’s take a closer look at the science behind why potatoes turn brown when peeled and what function the ice water plays in the process.
Enzymatic Browning
The specific enzymes responsible for the color change in potatoes are polyphenol oxidase and tyrosinase. These enzymes catalyze reactions that cause browning in a wide range of fruits and vegetables.
When a potato is peeled or cut into, these enzymes stored inside the cells are released and exposed to oxygen. They trigger a complex cascade of chemical reactions that transform phenolic compounds naturally present in the potato into brown pigments called melanins.
The melanin particles accumulate on the surface of the potato, creating the typical rusty brown discoloration you see on peeled or cut potatoes left out too long.
How Ice Water Inhibits Enzymatic Browning
This enzymatic process can be delayed by chilling the potatoes. The cold temperature of the ice bath reduces the kinetic energy of the enzymes. This slows down their activity and the entire chain of reactions leading to melanin formation.
Colder temperatures cause more sluggish molecular collisions and enzyme catalysis. The rate of chemical reactions decreases exponentially with decreasing temperature.
Storing the potatoes at just a few degrees above freezing optimally slows the potato flesh from turning brown. This buys some time before the oxidation reactions kick into high gear again upon returning to room temperature.
Role of Water
The water is also important, not just the cold temperature alone. Keeping the potatoes submerged in water limits their exposure to oxygen compared to leaving them out in the air. With less available oxygen, the enzymes have more limited substrates to work with, further reducing browning.
The water also helps remove phenolic compounds that contribute to browning reactions. This provides another line of defense against enzymatic oxidation and color change.
Other Ways to Prevent Browning
While ice water is one of the simplest ways to prevent browning raw potatoes, there are some other effective options as well:
- Acidulants – Lemon juice, vinegar, acidic fruit juices
- Antioxidants – Ascorbic acid, citric acid
- Blanching – Quick boiling then shocking in ice water
- Reducing agents – Sodium bisulfite
The acids in lemon juice or vinegar lower the pH on the potato surface, which slows enzyme activity. Antioxidants like vitamin C directly counteract the oxidative browning reactions.
Blanching boils away surface enzymes, while sulfite additives inhibit enzyme function. However, for basic home usage, an ice water bath provides an easy route to limit browning without extra ingredients or processing steps.
Does Water Temperature Matter?
You’ll often see references to soaking peeled potatoes in “ice water.” But does the water need to be super chilled, or is any cold water effective? Let’s take a look at how water temperature impacts browning.
Room Temperature Water
Using plain tap water at room temperature will provide some protection against browning versus leaving potatoes out in the air. The submersion in water isolates surfaces from oxygen and removes some phenolics.
However, room temperature alone does not have a meaningful impact on enzyme kinetics. Without a chilling effect, you’ll only get minimal slow-down of oxidation reactions at best.
Refrigerator Temperature Water
Cooler water from the refrigerator faucet provides enhanced benefits. Lower temperatures in the range of 40-50°F will decelerate enzyme activity, increasing the time before noticeable browning occurs.
This colder water better preserves the potatoes’ fresh appearance compared to room temperature soaking. It approximately doubles the time you have until browning develops.
Ice Water
For maximum browning prevention, use ice water. The frozen ice provides sub-zero chilling for a dramatic slow-down of enzymatic processes. This can extend the time before browning by 5-10 times compared to room temperature.
Ice water optimally pairs cold temperature effects with water isolation and starch removal. This triple combination provides the best defense against browning for the longest duration.
Frozen Potatoes
Freezing peeled potatoes prior to cooking prevents browning entirely. The near-freezing temperature arrests all enzyme activity. Frozen potatoes can be stored this way for months without issue.
However, frozen potatoes used immediately after peeling will generally turn brown once thawed. So freezing is more useful for long-term storage rather than preventing short-term browning.
Proper Ice Water Technique
For best results, follow these tips when using ice water for peeled potatoes:
- Use plenty of ice
- Allow 5-10 minutes soaking time
- Agitate potatoes mid-soak
- Change water as ice melts
- Pat dry potatoes before cooking
This ensures the potatoes are uniformly exposed to the chilled water for sufficient time. Swirling them mid-soak distributes temperature effects. Draining and patting dry prevents dilution of flavors when cooking.
Preparing an Ice Water Bath
Making an effective ice bath for potatoes only takes a few simple steps:
- Fill a large bowl halfway with cold tap water
- Add several cups of ice cubes
- Allow a minute for the water to cool fully
- Peel and cut potatoes into desired size pieces
- Submerge potato pieces in the ice bath
- Let soak 5-10 minutes, stirring occasionally
- Drain potatoes and pat dry before cooking as directed
The bowl size and amount of ice can be adjusted based on the potato quantity. Aim for at least a 1:1 ratio of ice to water for optimal chilling.
Try It Yourself!
See for yourself how effective an ice water soak is at preventing potato browning. Try this simple experiment:
- Peel 2 medium russet potatoes
- Cut one potato into slices and leave on a plate
- Cut the other potato into slices and place in ice water
- Observe both samples for 10 minutes
The potato left on the plate will start turning brown within minutes, while the ice water potato remains fresh-looking much longer. This clearly demonstrates the benefits of ice water immersion first-hand!
Frequently Asked Questions
Should you soak potatoes after cutting?
Yes, it’s ideal to soak potato pieces in ice water soon after cutting or peeling them. This prevents browning right from the start.
How long do you soak potatoes in ice water?
5-10 minutes is usually sufficient. Longer is okay if needed to finish prep work, but drain and pat dry before cooking.
Do potatoes soak up water when soaking?
A little, but not significantly. Patting dry with a towel after draining prevents excess water absorption.
Can you reuse potato soak water?
No, discard the water after each use. The starch and phenolic compounds released into it can promote browning.
Does soaking in salt water work?
Yes, a bit. The salt lowers water activity, which slows browning. But chilled water works better.
The Takeaway
Placing peeled or cut potatoes in ice water prevents enzymatic browning reactions, retains moisture, improves texture, and makes the potatoes easier to handle. The chilled water optimally slows enzyme activity while providing a protective aqueous environment.
Compared to room temperature water, ice water extends the time before browning by 5-10 times. Following proper technique allows you to keep potatoes fresh-looking and ready for cooking or other prep work.
So next time a recipe calls for peeled potatoes, be sure to have a bowl of ice water ready! This simple trick locks in maximum quality and appearance for perfect potatoes every time.
