Introduction: Why Alternate Alkaline and Acid Cleaning?
Production managers at meatpacking plants often ask: why not use just one type of cleaning? Using only alkaline cleaning or only acid cleaning looks simpler and cheaper, but it leads to:
- Buildup of residues that a single agent cannot remove (fats vs. minerals)
- Formation of resistant biofilms (the matrix protects microorganisms)
- Accelerated equipment corrosion (continuous exposure to extreme pH)
- Audit nonconformities (positive swabs, high ATP readings)
This technical article explains when to use alkaline cleaning and when to use acid cleaning in CIP (Clean-in-Place) protocols, covering:
- Differences in how each one works
- Types of soil each method removes
- Recommended chemicals (caustic soda, nitric acid)
- Correct step sequencing
- Ideal frequency for each type of cleaning
1. Alkaline Cleaning: Removing Fats and Proteins
1.1 How It Works
Alkaline cleaning (pH 11-14) uses sodium hydroxide (caustic soda) or alkaline detergents for:
-
Saponification of fats:
- Fats (triglycerides) + NaOH → soaps (water soluble) + glycerol
- An irreversible chemical reaction that turns insoluble fat into soluble compounds
-
Protein denaturation:
- Alkaline pH breaks peptide bonds (tertiary/quaternary structure)
- Coagulated proteins (blood, meat residues) dissolve
-
Biofilm dispersion:
- The alkali attacks the polysaccharide matrix (EPS, Extracellular Polymeric Substances)
- The biofilm breaks apart and is carried away by the flow
Ideal temperature: 70-80°C (speeds up saponification and dissolution)
1.2 Chemicals Used
Caustic Soda (NaOH), 1.5-3% Concentration
Advantages:
- ✅ Highly effective at saponifying fats
- ✅ Affordable and economical
- ✅ Fast acting (20-30 minutes)
- ✅ Compatible with stainless steel at controlled concentrations
Disadvantages:
- ⚠️ Corrosive (requires full PPE)
- ⚠️ Can damage aluminum, copper and zinc (choose the right concentration)
- ⚠️ Alkaline residues must be neutralized before sanitizing
Chlorinated Alkaline Detergents (pH 12-13)
Advantages:
- ✅ Combine alkaline cleaning with light sanitizing (active chlorine)
- ✅ Safer than pure caustic soda (lower pH)
- ✅ Formulations designed for CIP (defoamers, sequestrants)
Disadvantages:
- ⚠️ Cost 3-5 times more than caustic soda
- ⚠️ Chlorine can be inactivated by organic matter (reducing its sanitizing effect)
1.3 Types of Soil Removed
| **Type of Soil** | **Alkaline Cleaning Effectiveness** | **Notes** |
|---|---|---|
| Fats (animal, vegetable) | ⭐⭐⭐⭐⭐ | Complete saponification |
| Coagulated proteins (blood) | ⭐⭐⭐⭐⭐ | Denaturation and dissolution |
| Organic biofilms | ⭐⭐⭐⭐ | Breakdown of the EPS matrix |
| Mineral scale (limescale) | ⭐ | Does not remove it and may even make it worse (salt precipitation) |
| Milk residues (milkstone) | ⭐⭐ | Removes the organic part, not the mineral part |
2. Acid Cleaning: Removing Mineral Scale
2.1 How It Works
Acid cleaning (pH 1-3) uses nitric acid, phosphoric acid or acid detergents for:
-
Dissolving minerals:
- Calcium carbonate (limescale) + HNO₃ → Ca(NO₃)₂ (soluble) + CO₂ + H₂O
- Calcium phosphates (milkstone) + HNO₃ → Ca(NO₃)₂ (soluble) + H₃PO₄
-
Passivating stainless steel:
- Nitric acid forms a protective chromium oxide layer (Cr₂O₃)
- Increases corrosion resistance
-
Removing rust:
- Iron oxide (Fe₂O₃) + HNO₃ → Fe(NO₃)₃ (soluble)
Ideal temperature: 50-60°C (avoids thermal decomposition of the acids)
2.2 Chemicals Used
Nitric Acid 53%, Working Concentration 0.5-2%
Advantages:
- ✅ Dissolves carbonates and phosphates efficiently
- ✅ Passivates stainless steel (extra protection)
- ✅ Leaves no organic residue (volatilizes or rinses off easily)
Disadvantages:
- ⚠️ Highly corrosive (concentrated)
- ⚠️ Releases nitrous fumes (NOx) if heated above 70°C
- ⚠️ Incompatible with bases (violent reaction, never mix)
Phosphoric Acid 85%, Working Concentration 1-3%
Advantages:
- ✅ Less corrosive than nitric acid
- ✅ Effective at removing milkstone
- ✅ Safer to handle
Disadvantages:
- ⚠️ Can leave phosphate residue (requires thorough rinsing)
- ⚠️ Less effective at passivating stainless steel
Acid Detergents (pH 2-3)
Advantages:
- ✅ Balanced formulations (acids + surfactants + sequestrants)
- ✅ Safer than pure acids
- ✅ Reduce foam formation
Disadvantages:
- ⚠️ Cost 4-6 times more than pure acids
2.3 Types of Soil Removed
| **Type of Soil** | **Acid Cleaning Effectiveness** | **Notes** |
|---|---|---|
| Calcium carbonate (limescale) | ⭐⭐⭐⭐⭐ | Complete dissolution |
| Calcium phosphates (milkstone) | ⭐⭐⭐⭐⭐ | Efficient dissolution (especially phosphoric) |
| Iron oxide (rust) | ⭐⭐⭐⭐ | Removes rust stains |
| Hard water residues | ⭐⭐⭐⭐⭐ | Prevents salt buildup |
| Fats | ⭐ | Does not remove them (requires alkaline) |
| Proteins | ⭐⭐ | Very low effectiveness |
3. When to Use Each Type of Cleaning: Decision Criteria
3.1 By Type of Equipment
Equipment with a High Fat Load:
Examples: Brine tanks, injectors, tumblers (massagers), smokehouses
Protocol:
- Alkaline cleaning 2-3 times a week (70-80°C, 2% caustic soda)
- Acid cleaning once a week (50°C, 1% nitric acid) to remove water minerals
Rationale: Fats predominate, so alkaline cleaning is the priority. The acid step complements it by removing mineral deposits from the process water.
Equipment with a High Mineral Load:
Examples: Milk tanks, pasteurizers, UHT systems, evaporators
Protocol:
- Alkaline cleaning once a day (75°C, chlorinated alkaline detergent)
- Acid cleaning once a day (alternating or after the alkaline step), 55°C, 2% phosphoric acid
Rationale: "Milkstone" (calcium phosphate) builds up quickly. Daily acid cleaning is essential.
Mixed-Process Equipment (Meat + Hard Water):
Examples: Slaughter lines, rails, carts, cutting tables (adapted CIP)
Protocol:
- Alkaline cleaning daily (80°C, 1.5% caustic soda)
- Acid cleaning twice a week (50°C, 0.5% nitric acid)
Rationale: Protein and fat residues are removed daily. Minerals build up more slowly (less frequent cleaning).
3.2 By Water Quality
Soft Water (< 50 mg/L CaCO₃):
- Low mineral buildup
- Mostly alkaline cleaning (3-4 alkaline : 1 acid)
Moderately Hard Water (50-150 mg/L CaCO₃):
- Moderate limescale buildup
- Balanced cleaning (2 alkaline : 1 acid, or alternating)
Very Hard Water (> 150 mg/L CaCO₃):
- Rapid scale buildup
- Frequent acid cleaning (1 alkaline : 1 acid, alternating)
- Recommendation: Install a water softener (reduces acid costs)
3.3 By How Often the Equipment Is Used
Continuous Use (3 shifts, 24 h):
CIP protocol:
- Morning: Alkaline cleaning (start of the 1st shift)
- Afternoon: Acid cleaning (start of the 2nd shift)
- Night: Final rinse + sanitizing (start of the 3rd shift)
Rationale: High throughput means residues build up fast. Alternating daily prevents buildup.
Intermittent Use (1-2 shifts/day):
CIP protocol:
- Even days: Alkaline cleaning + rinse + sanitizing
- Odd days: Alkaline cleaning + acid cleaning + rinse + sanitizing
Rationale: Lower frequency allows a full protocol on alternate days.
4. Correct Sequencing of CIP Steps
4.1 Standard Protocol: Alkaline First, Then Acid
Full sequence (6 steps):
- Pre-rinse (water at 40-50°C, 5-10 min): removes coarse residue
- Alkaline cleaning (2% caustic soda, 75°C, 20-30 min): removes fats and proteins
- Intermediate rinse (water at 40°C, 5 min): removes alkaline residue
- Acid cleaning (1% nitric acid, 55°C, 15-30 min): removes minerals
- Final rinse (water at 30°C, 5-10 min): complete neutralization
- Sanitizing (hypochlorite 200 ppm or peroxide 2%, 10 min): eliminates microorganisms
Total time: 70-100 minutes
Why alkaline before acid?
- Fats and proteins form a layer that keeps the acid from reaching the mineral scale
- Removing the organic matrix first exposes the minerals to acid cleaning
- Reversing the order makes both agents less effective
4.2 Simplified Protocol: Alkaline Only (Daily Use)
Sequence (4 steps):
- Pre-rinse (5-10 min)
- Alkaline cleaning (20-30 min)
- Final rinse (5-10 min)
- Sanitizing (10 min)
When to use it:
- Equipment with little mineral buildup
- Daily cleaning (acid only 1-2 times a week)
- Soft water
Total time: 40-60 minutes
4.3 Shock Protocol: Intensive Acid (Maintenance)
Sequence (5 steps):
- Pre-rinse (10 min)
- Alkaline cleaning (30 min): removes biofilms
- Intermediate rinse (5 min)
- Extended acid cleaning (2% nitric acid, 60-90 min, 60°C): removes heavy scale
- Final rinse (10 min) + sanitizing (10 min)
When to use it:
- Equipment with heavy scale (visible white or yellowish deposits)
- Monthly preventive maintenance
- After periods of inactivity (collective vacations, shutdowns)
Total time: 125-155 minutes
5. Temperature Control: Impact on Effectiveness
5.1 Temperature in Alkaline Cleaning
| **Temperature** | **Effectiveness** | **Energy Consumption** | **Risk** |
|---|---|---|---|
| 40-50°C | Low (slow saponification) | Low | Ineffective on saturated fats |
| 60-70°C | Moderate (good for formulated detergents) | Moderate | Suitable for alkaline detergents |
| 75-80°C | High (ideal for caustic soda) | High | Excellent saponification |
| > 85°C | Very high, but with risks | Very high | Thermal decomposition of caustic soda, corrosion |
Recommendation: 75°C for caustic soda, 65°C for alkaline detergents.
5.2 Temperature in Acid Cleaning
| **Temperature** | **Effectiveness** | **Risk** |
|---|---|---|
| 30-40°C | Low (slow mineral dissolution) | Safe, but inefficient |
| 50-60°C | Excellent (fast dissolution, no decomposition) | **Ideal temperature** |
| > 70°C | High dissolution, but high risk | Nitrous fumes (NOx), accelerated corrosion |
Recommendation: 55°C for nitric acid; avoid > 65°C.
6. Effectiveness Indicators: How to Validate Cleaning
6.1 Visual Inspection
After alkaline cleaning:
- ✅ Shiny surfaces with no greasy film
- ✅ No protein residue (dark stains)
- ❌ White or yellowish stains (minerals, acid step needed)
After acid cleaning:
- ✅ Even surfaces with no mineral deposits
- ✅ Stainless steel with a metallic sheen (passivation)
- ❌ Dark or greasy stains (alkaline step needed)
6.2 ATP (Adenosine Triphosphate) Test
Principle: Measures the presence of organic matter (microbial cells + food residues).
Reference values (RLU, Relative Light Units):
- < 100 RLU: Excellent cleaning
- 100-300 RLU: Acceptable cleaning
- > 300 RLU: Inadequate cleaning (repeat the CIP)
Caution: ATP does not detect minerals. Use visual inspection as a complement.
6.3 Microbiological Swabs
Protocol:
- Swab the surface after the full CIP (post-sanitizing)
- Plate on PCA (mesophiles) and Sabouraud agar (fungi)
- Incubate for 24-48 h
Reference values:
- < 10 CFU/cm²: Compliant
- 10-50 CFU/cm²: Warning (review sanitizing)
- > 50 CFU/cm²: Nonconforming (review the full CIP)
7. Common Mistakes and How to Avoid Them
7.1 Mistake: Using Alkaline Cleaning Only
Consequence:
- Progressive mineral buildup ("milkstone", limescale)
- A rough surface that helps biofilms adhere
- Lower heat-exchange efficiency (pasteurizers)
Solution: Introduce acid cleaning at least once a week.
7.2 Mistake: Mixing Alkaline and Acid
Consequence:
- A neutralization reaction that wipes out effectiveness entirely
- NaOH + HNO₃ → NaNO₃ + H₂O (a neutral salt with no cleaning action)
- Heat release (exothermic reaction)
Solution: A thorough intermediate rinse (5-10 minutes) between the alkaline and acid steps.
7.3 Mistake: Excessive Temperature in Acid Cleaning
Consequence:
- Thermal decomposition of nitric acid, releasing nitrous fumes (NOx, toxic)
- Accelerated corrosion of stainless steel (breakdown of the passive layer)
Solution: Limit the temperature to a maximum of 65°C.
7.4 Mistake: Incorrect Concentration
Concentration too low:
- Excessive cleaning time (> 60 min)
- Scale not completely removed
Concentration too high:
- Corrosion risk (caustic soda > 5%, acid > 3%)
- High cost (wasted product)
- Health risk to operators (PPE may not be enough)
Solution: Follow the manufacturer's recommended ranges and validate with an effectiveness test.
8. Frequently Asked Questions (FAQ)
8.1 Can I use vinegar or lemon for acid cleaning?
Not recommended for industrial CIP.
- Acetic acid (vinegar): pH ~3, low effectiveness on mineral scale, leaves a residual odor
- Citric acid (lemon): pH ~2, better than vinegar, but costs 10 times more than nitric acid
Application: Citric acid can be used in small artisanal operations.
8.2 How often should I do acid cleaning?
It depends on water hardness:
- Soft water (< 50 mg/L CaCO₃): once a week
- Moderately hard water (50-150 mg/L): twice a week, or alternating 1 alkaline : 1 acid
- Hard water (> 150 mg/L): alternating daily (day 1 alkaline, day 2 acid)
8.3 Does acid cleaning corrode stainless steel?
Not if it is used correctly:
- Nitric acid at 0.5-2% and a temperature < 65°C passivates stainless steel (protects it)
- Acid > 5% or a temperature > 80°C can cause corrosion
Stainless steel grades:
- AISI 304: More sensitive; use nitric acid (passivating)
- AISI 316: More resistant (contains molybdenum)
8.4 Can I use caustic soda on aluminum?
No. Caustic soda attacks aluminum:
- 2 Al + 2 NaOH + 2 H₂O → 2 NaAlO₂ + 3 H₂↑ (hydrogen gas)
- The aluminum surface becomes dull and rough and loses strength
Alternative: Neutral or mildly alkaline detergents (pH 9-10).
8.5 How should CIP effluents be disposed of?
Alkaline effluents:
- Neutralize with acid (citric, dilute sulfuric) to pH 6-9
- Send to the WWTP (Wastewater Treatment Plant)
Acid effluents:
- Neutralize with a base (lime, dilute caustic soda) to pH 6-9
- Send to the WWTP
Caution: Discharging directly into the sewer system without neutralization violates environmental law (CONAMA Resolution 430/2011, Brazil's federal standard for effluent discharge).
8.6 What does alkaline cleaning cost compared with acid cleaning?
Example (mid-sized meatpacking plant, 1,000 L of CIP solution per day):
Alkaline cleaning (2% caustic soda):
- Consumption: 20 kg of caustic soda per day
- Cost: economical and affordable
Acid cleaning (1% nitric acid):
- Consumption: 10 L of acid per day
- Cost: moderately higher than alkaline
Alternating protocol (3 alkaline : 1 acid per week):
- Average cost: a balanced, sustainable operating expense
9. Boreto & Cardoso®: Supplier of CIP Products
9.1 Available Products
Caustic Soda (NaOH):
- Certificate of Analysis
- Safety Data Sheet (SDS)
- Packaging: 99% micropearls 25 kg, 50% solution in 50 kg jerrycans, 1,000 L IBC
Nitric Acid 53%:
- Certificate of Analysis
- Safety Data Sheet (SDS)
- Packaging: 25 kg jerrycans, 1,000 L IBC
Formulated Alkaline and Acid Detergents:
- Certificate of Analysis
- Safety Data Sheet (SDS)
- Packaging: 25 L jerrycans
9.2 Why Boreto & Cardoso®
With 53 years supplying chemical inputs to the food industry, Boreto & Cardoso® distributes caustic soda, nitric acid and formulated detergents from certified suppliers. Every product comes with its Certificate of Analysis. We also provide the Safety Data Sheet (SDS) and the other documents required for legal and quality compliance.
Our ISO 9001 certification and long-standing relationships with well-known manufacturers ensure a consistent, reliable supply of products for CIP cleaning.
Conclusion: Alternating Alkaline and Acid Ensures Complete Cleaning
Combining alkaline and acid cleaning is a complementary strategy, with no redundancy:
- Alkaline: Removes fats, proteins and organic biofilms
- Acid: Removes minerals, passivates stainless steel and prevents scale
Using only one type leads to:
- Buildup of soil that is never removed
- Rough surfaces (which favor biofilms)
- Corrosion or reduced equipment efficiency
A balanced protocol:
- Equipment with a high organic load: 3 alkaline : 1 acid
- Equipment with a high mineral load: 1 alkaline : 1 acid
- Validate effectiveness with visual inspection, ATP and swabs
Note to the reader This article brings together technical information drawn from various sources, with the aim of broadening knowledge about the raw materials mentioned. It is for information purposes only and does not represent any indication of application, formulation or direct recommendation of use on the part of Boreto & Cardoso. With 53 years of experience, Boreto & Cardoso® operates strictly as a supplier of chemical inputs for a wide range of applications, and it is the responsibility of each user to verify the suitability and compliance of their application.
📞 Contact Information
Boreto & Cardoso® - Chemical Inputs Distributor
📱 Phones: +55 11 3931-1722 +55 11 2366-6260
📧 Email: boreto@boreto.com.br
📍 Address: Rua Alagoas, 30 | Recanto Silvestre Santana de Parnaíba - SP | CEP 06530-245
🌐 Website: www.boreto.com.br
🏆 Certification: ISO 9001 - Quality Management