The formula of taste: how Brix, acidity and sensory neuroscience define the ideal fruit

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Why perfect-looking fruits often turn out tasteless and how physicochemical markers help find "that very" taste

How do you choose tasty fruits? And how do you choose the right, delicious puree or concentrated juice for industrial processing? In the first case, you can go to the market and taste it. In the second case, it is harder — you need to order samples, ensure speed and integrity during delivery. And that is no easy task in today's world of sanctions.

ANIX sends dozens of samples to its clients every week and knows this problem firsthand. Quite often, our clients' feedback is subjective — sour, watery, or on the contrary too thick or empty. In some cases, this is fixable: it is enough to clearly articulate the shortcoming and select another batch or product. For such a dialogue to work, the subjective component must be removed and product characteristics expressed in the most objective, numeric terms possible.

Differences in taste between different people are natural. Changes in a person's taste perception over time are also natural and depend on a great many factors.

We asked ourselves how to make a conscious choice of tasty fruits and purees made from them, using three of the most popular fruits as examples: apple, peach, and apricot. What objective numeric characteristics could be used to convey a taste close to ideal? We have also included materials on cultivation, quality assessment, and fruit selection that should help better understand the stages of fruit puree production. And we think they will not be superfluous when buying fresh fruit at the market.

We present the results of the study to you.

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Article contents

Chapter 1. Why the same fruit tastes delicious to one person and bland to another

Sensory neuroscience: flavor, the orthonasal and retronasal pathways of olfaction, 25 types of bitterness receptors, and the qualia phenomenon.

Chapter 2. How scientists measure taste: the Brix scale, BrimA, and firmness by penetrometer

Objective physicochemical quality markers. A refractometer in simple words, the sugar-acid index, and the physics of mealiness.

Chapter 3. How to choose a tasty apple without a laboratory

UNECE FFV-50 standards. A selection checklist based on skin, russeting, and firmness. A register of the TOP-10 dessert varieties.

Chapter 4. How to choose a sweet and fragrant peach

The problem of immaturity and climacteric fruits. The stem-end test, the chlorophyll index, and a register of TOP-10 varieties.

Chapter 5. How to choose the tastiest apricot

Organic acids: skin citrates versus flesh malates. Buying mistakes and a register of TOP-10 varieties.

Chapter 6. Comparison of crops and the influence of terroir on fruit quality

A summary table of parameters. How the sun, climate, and soils of Serbia, Spain, Turkey, and Southern Europe shape a unique taste.

Chapter 7. Geographic map of preferences: tastes are indeed disputed

Why tastes in Germany, Italy, Spain, and different regions of Russia differ radically at the biochemical level.

Chapter 8. From fruit to juice and puree: biochemical transformations during processing

Loss of aroma during pasteurization. Direct-pressed juice, nectar, concentrate, and puree. Technologies: LAB fermentation and cold plasma.

Chapter 9. The FPI palatability index and incoming quality control of imported raw materials

The 100-point Fruit Palatability Index rating system. How B2B purchases of juice raw materials guarantee a stable taste without a "sensory sacrifice".

Section 10. FAQ: Answers to popular questions about fruit taste

Simple answers to complex questions about Brix, storage, ripeness, and the nutritional properties of stone fruits and pome fruits.

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Chapter 1. Why the same fruit tastes delicious to one person and bland to another

Taste is not just a signal sent from the tongue to the brain. It is a highly complex multisensory experience that physiologists call flavor (flavor). When you bite into a slice of fruit, a whole chain of processes is triggered:

• What the tongue detects: Sweet, sour, bitter, salty, and umami (the so-called "fifth taste" — a glutamic, rich, protein-like or meaty taste perceived by specific L-glutamate receptors). Sweet substances bind to the T1R2/T1R3 receptor dimers on the membranes of taste cells. Sour tastes are detected directly through ion channels that respond to the concentration of free hydrogen protons H⁺. Bitter compounds (for example, polyphenols — natural antioxidants with a bitter-astringent taste) activate the monomeric receptors of the T2R family.
• What the nose senses (aroma): It provides up to 80% of the taste sensation! Smell works through two pathways. The orthonasal pathway is when you simply hold the fruit to your nose and inhale its scent. The retronasal pathway is the key stage: while chewing, the warm flesh heats up, volatile organic compounds (VOCs — Volatile Organic Compounds that determine the fruit's aroma) evaporate and rise through the nasopharynx to the receptors. It is precisely the retronasal pathway that lets you tell an apple from a pear with your nose closed.
• Fruit texture: Whether the flesh crunches or melts, how dense, fibrous, or watery it is.
• Temperature and juiciness: High juiciness accelerates the release of water-soluble compounds and enhances sweetness.
• Personal experience and expectations: If you grew up on the classic sour Antonovka, the sweet Australian variety Pink Lady may seem "fake" or cloying to you.

Fig. 1. Anatomy of flavor: the interaction of the tongue's taste receptors and the retronasal olfactory pathway during chewing

Closely related to this is another important aspect of physiology. For a long time, popular literature was dominated by the myth of the "tongue taste map", according to which sweetness is perceived only by the tip of the tongue, sourness by the lateral zones, bitterness by the root, and saltiness by the edges. Modern molecular biology has completely refuted this idea. In fact, receptors for all five basic tastes (including umami) are expressed in taste points across the entire surface of the tongue. The difference lies only in sensitivity thresholds and the relative density of receptor proteins on the cells: the tip of the tongue has a slightly lower activation threshold for sweetness, but the recognition of all tastes occurs over the whole area (Fig. 2).

Fig. 2. Tongue taste map: the modern scientific view of receptor distribution. Receptors for all basic tastes (sweet, sour, salty, bitter, and umami) are located over the entire surface of the tongue but have an uneven distribution density. The side callouts show a molecular close-up of taste buds and cellular receptors.

Chapter 2. How scientists measure taste: the Brix scale, BrimA, and firmness by penetrometer

To rule out the subjectivity of tasters, the food industry and agronomy have digitized taste using three main physicochemical indicators.

1. The Brix scale — what it is in simple words

The Brix value (Brix, °Bx) is the percentage of soluble solids (mostly simple sugars: fructose, glucose, and sucrose) in the fruit's liquid juice. It is measured with a special device — a refractometer. The device is simple in design and resembles a miniature spyglass: you drop a drop of fruit juice onto the sample plate, close the cover, and look through the eyepiece toward the light. The exact sugar number is read from the refraction scale of the light beam.

Fig. 3. Determining the Brix value using a drop of fresh fruit juice on an optical refractometer

But sugar alone, without acid, makes a fruit cloying, "flat", and lifeless. A balanced taste requires sourness, which is provided by the fruit's titratable acidity (TA — the total concentration of free acids determined in the laboratory by titrating the juice with an alkali).

2. The BrimA index — the balance of sweet and sour

In international practice, instead of the simple Brix/Acid division, the BrimA index (short for Brix minus Acid — "Brix minus Acidity") is increasingly used. This indicator predicts whether consumers will like a fruit much more accurately, since it takes into account the peculiarities of human physiology.

The BrimA formula is calculated as follows:

where:

• Brix — the sweetness indicator (the percentage of dissolved solids);
• Acid — titratable acidity (the percentage of free acids);
• k — a special comparison multiplier. It is needed because of physiology: our tongue reacts to acidic hydrogen protons several times more acutely than to sugar molecules. A fluctuation in acidity of even 0.2% instantly changes the taste from harmonious to sour, while a change in sugar of the same 0.2% would go practically unnoticed. The multiplier k artificially "amplifies" the role of acidity in the formula, making the math work just like our tongue does.

Organic acid molecules (Acid) affect the tongue's receptors 2.5 times more strongly than sugars (Brix). To balance perception in the brain (achieve BrimA ≥ 9.5), a 2.5 times higher concentration of sugar molecules is required to neutralize the sourness impulses.

Where do you get the value of the coefficient k?
This coefficient does not need to be calculated yourself — it is a ready-made scientific constant for each type of fruit, established through large-scale tasting studies (above all, at the University of California, Davis — UC Davis, and the US Department of Agriculture — USDA):

• Apple, peach, apricot, pear, plum (fruits where soft malic acid predominates): k = 2.5 (some methods allow a range of 2.0–3.0).
• Sour cherry, sweet cherry, garden strawberry, grapes (berries with more pronounced tartaric and citric acids): k = 3.0.
• Citrus fruits (orange, mandarin, lemon) and blackcurrant (crops with a high content of sharp citric acid): k = 4.0 or k = 5.0.

To calculate BrimA for other berries and exotic fruits, baseline coefficient values can be found in academic databases and postharvest handling guides (for example, in the registries of UC Davis Postharvest Technology Center or in the quality specifications of USDA Fruit and Vegetable Grades and Standards).

Where do BrimA threshold values come from and how should they be assessed?
These thresholds are determined based on Consumer Sensory Panels. Large-scale tests involving hundreds of consumers help find the numeric boundary of satisfaction (when more than 80% of people call the fruit's taste good and balanced).
BrimA threshold standards for key crops:

• Apple, pear: excellent taste — ≥ 9.5.
• Peach, nectarine, apricot, plum: excellent taste — ≥ 9.5–10.0.
• Sour cherry, sweet cherry: excellent taste — ≥ 10.0.
• Garden strawberry: excellent taste — ≥ 9.0.

The BrimA interpretation scale: how do the numbers translate into taste?
The BrimA index has no physical units, but its numeric value clearly maps to the consumer rating of taste:

• Below 8.0 — Mediocre or sour taste. There is too little sugar or acidity goes off the scale. The fruit seems "green", "woody", or aggressively sour. Consumer satisfaction drops below 40%.
• From 8.0 to 9.4 — Acceptable taste (Class II). This is the baseline level of inexpensive mass retail. The fruit is edible, but the taste is "flat" or slightly empty. The boundary here is smooth: a fruit with BrimA 9.4 will not be terrible, it simply sits at the transition threshold, where sourness already begins to mask sweetness.
• From 9.5 to 11.0 — Excellent, balanced taste (Class I). The golden standard. Sugar and acid support each other perfectly. More than 80% of people rate such a taste as harmonious. This is the target for purchasing quality raw materials.
• Above 11.0 — Premium, outstanding taste (Extra class). Very sweet fruits with bright varietal aroma. More than 95% of people give it the highest score.

How does the math of taste compensation work in practice?
The main advantage of the BrimA index is the demonstration of the masking effect. High sugar can smooth out (compensate for) high acidity. Let us consider two real examples for apple (using the constant k = 2.5):

• Case 1 (Low sugar): The apple has a titratable acidity of 0.60% and a Brix of 10.0% (an average underripe apple). BrimA = 10.0 - (2.5 · 0.60) = 8.5 (mediocre taste)
• Case 2 (High sugar): The apple's acidity is exactly the same — 0.60%, but the Brix is 14.0% (a fully sun-ripened apple). BrimA = 14.0 - (2.5 · 0.60) = 12.5 (premium taste)

Although the acid in both apples is absolutely equal, the second one, thanks to its high Brix, is perceived as exceptionally tasty and sweet, while the first is perceived as annoyingly sour. The BrimA index perfectly digitizes this physiological illusion.

3. Flesh firmness and penetrometer

Firmness is measured with a device called a penetrometer, which presses a metal plunger of a certain diameter into the fruit flesh. It is measured in kg/cm². Why do overripe apples become mealy and "cottony"? The walls of plant cells contain the rigid polysaccharide protopectin, which binds cells to each other (like cement binds bricks). During ripening, enzymes convert protopectin into soluble pectin. Cell adhesion drops, turgor (the internal water pressure in plant cells that provides their elasticity) disappears, and the apple loses its juiciness, turning into mush.

Chapter 3. How to choose a tasty apple without a laboratory

Quality dessert apples are regulated by the UNECE FFV-50 standard. The optimal Brix for purchase is at least 10 °Bx (for premium varieties — from 12.5 °Bx), titratable acidity — 0.3–0.8%, and firmness by penetrometer at the intake stage — 5–7 kg/cm² (at values below 4.5 kg/cm² the flesh becomes cottony).

TOP-10 apple varieties by organoleptic properties

Chapter 4. How to choose a sweet and aromatic peach

The peach (Prunus persica) is a capricious climacteric fruit (that is, able to ripen after being picked from the branch under the influence of the ethylene gas it emits itself). Retail chains often buy it underripe (at the stage of technical ripeness with a firmness of 5–7 kg/cm²) so that it withstands the journey. The minimum UNECE FFV-26 standard requires Brix from 9 °Bx, but the real flavor only appears from 11 °Bx, and a level above 13 °Bx is considered premium.

Fig. 6. Determining the chlorophyll index with a non-contact spectrometer DA-Meter directly on the branch before harvest

TOP-10 peach and nectarine varieties

Chapter 5. How to choose the most delicious apricot

The apricot (Prunus armeniaca) is regulated by the UNECE FFV-02 standard. The optimal Brix of a ripe fruit is 12.5–16.0 °Bx. The main biochemical feature of the apricot lies in the interaction of acids: the fruit skin accumulates citric acid and its salts (citrates), which give a sharp sourness, while the flesh contains soft malic acid and its salts (malates). The higher the share of malates (malic acid salts), the softer and more harmonious the apricot's taste.

TOP-10 apricot varieties

Chapter 6. Comparison of crops and the influence of terroir on fruit quality

Let us consolidate the physicochemical and logistical parameters of pome and stone fruit crops into a single comparative table.

Influence of geographic origin (terroir) on fruit quality

Fig. 7. Mediterranean terroir: a peach orchard in the province of Murcia (Spain) during the harvest period

Terroir combines climatic features, sunshine hours, soil type and precipitation, shaping a unique biochemical composition of the fruit.

Chapter 7. A geographic map of preferences: tastes really do differ

National consumer preferences have a real biochemical basis. What is valued in Munich may be rejected in Madrid.

• Northern Russia: In conditions of insufficient solar warmth, the body subconsciously perceives sugars in fruit as a quick source of energy. Consumers choose the largest dense fruit with maximum sweetness. Tolerance for tartness in stone fruits is extremely low.
• Southern Europe: Consumers are used to an abundance of local seasonal fruit. They value a balanced flavor. The presence of fresh organic tartness (as in Reinette Simirenko) is perceived positively and associated with the fruit's naturalness.
• Germany: German consumers value moderate sweetness and a high share of organic produce. Crunchy sweet-tart bicolored apples (Elstar, Jonagold) lead the way. Fruit caliber must be strictly medium (75–80 mm), convenient for packing in trays.
• France: Rich aromatics and texture are appreciated. Melting white and flat peaches with a strong lactone profile (delicate coconut-creamy notes) and moderate sugar are popular.
• Italy: Preference is given to large fruit with high sweetness and soft, non-aggressive acidity, grown on the volcanic soils of Trentino.
• Spain: Spaniards are accustomed to the freshest possible fruit "straight off the branch" and have zero tolerance for acid. Only sub-acid stone fruit varieties are chosen (fruit with reduced acid content that has a pronounced sweet, honeyed flavor even at partial ripeness), having a honeyed taste and glossy skin.
• Turkey: High demand for sweet apricots (white and orange) and peaches. The presence of pronounced acid in the flavor is associated with unripe fruit.
• Middle East: An impeccable appearance of the fruit as a table decoration is important. Giant sweet red apples (Red Delicious, Gala Royal) with a perfect glossy surface free of blemishes are popular.

Chapter 8. From fruit to juice and puree: biochemical transformations during processing

Why does an imported peach from Spain that has traveled thousands of kilometers in a refrigerated truck sometimes turn out sweeter and more aromatic than a "local" one from the shelf? The answer is simple: professional suppliers measure fruit firmness with a penetrometer right at the moment of harvest, carefully calibrate the fruit, and strictly maintain the temperature regime along the entire logistics route.

The same principle of precise biochemical control is applied when processing fruit into concentrated juices and aseptic purees.

Fig. 8. A production line for gentle aseptic concentration and packaging of fruit puree at a plant

Modern Flavor Enhancement Technologies

The industry uses innovative approaches to create premium flavor profiles:

1. Directed LAB fermentation: Bacteria of Lactobacillus plantarum process free sugars (reducing caloric content by 20%), releasing soft lactic acid. The flavor profile becomes velvety, and the content of volatile aromatic compounds increases 2–3 times.

Fig. 9. Industrial bioreactors for directed lactic acid fermentation of fruit juices

2. Cold plasma: Non-thermal treatment of juice with electrical discharges. It completely destroys bacteria and breaks down oxidative enzymes (apple juice no longer darkens), preserving 100% of vitamin C and native aroma without thermal heating.

Fig. 10. Sterilization and enzyme inactivation of apple juice using cold plasma

Physicochemical Markers of the Ideal Flavor of Fruit Purees

A set of physicochemical indicators is used to objectively assess how well an industrial fruit puree or concentrate matches the ideal flavor profile. However, in the real practice of B2B supplies, rigid theoretical standards often clash with climatic, varietal, and economic realities. Every season, ANIX holds dozens of meetings with suppliers to select the optimal combination of quality and cost of the products offered.

The key markers in quality control are:

• Ripeness index (Ratio): It is calculated by the formula:
  Ripeness index (Ratio)

  Ratio =

  Brix

  Acidity (TA)
  The Ratio parameter (from the English ratio — «relation») is an internationally recognized term that technologists around the world use in contractual specifications for raw material supplies.
  *In simple terms:* this index shows how many times more sugar there is in the fruit than organic acids.
  • Brix measures the percentage of dissolved sugars (sweetness).
  • Titratable acidity measures the total percentage of free organic acids (the tartness) — mainly malic or citric acid depending on the fruit. The term «titratable» means that the acidity is determined by laboratory titration (neutralization with an alkali to the equivalence point).
  For example, if apple puree has a Brix of 12.0% and a titratable acidity of 0.4%, then their Ratio is equal to 12.0 / 0.4 = 30.0, since without a light tartness the natural sweetness seems lifeless.
  
  From the practical experience of orange raw material supplies: a Ratio within 8–12 gives a very sour taste, values of 13–16 are near the benchmark of balance, and readings of 18 and above give a pronounced sweetness.

  Acid is not just «tartness»; it is the framework that holds the entire aroma of the fruit. If the framework collapses (Ratio shoots up), the flavor «falls apart».

  The universal scale of flavor perception through Ratio looks like this:

  • Ratio < 10–12: Predominance of acidity. The taste is immature, astringent, grassy. It strains the receptors.
  • Ratio 12–15 (Golden standard): Peak of balance. Organic acids accentuate the natural sugar. The taste is fresh, full-bodied, noble.
  • Ratio > 16–18: Suppression of acidity. Monotonous sweetness prevails. The taste degrades, and the volatile aromas of the fruit «drown» in the sugar.

  Physicochemical profiles of fruits striving for the ideal:

  1. Apple (Balanced-type varieties) — for puree with the vivid taste of a fresh apple:
     Brix: 11.5°–12.0° | Acidity: 0.80%–0.90% | Ratio: 13.0–14.5
  2. Peach (Premium Puree) — the peach has a peculiarity (low natural acidity), because of which it is easy to let it «slide» into cloying sweetness. But premium raw material must maintain the balance:
     Brix: 10.5°–11.5° | Acidity: 0.70%–0.85% | Ratio: 13.0–15.0
  3. Apricot (Specific profile) — the only one of the three that, thanks to its high potassium content and specific acids, can maintain organoleptic balance at the lower limit:
     Brix: 11.0°–12.5° | Acidity: 0.90%–1.10% | Ratio: 11.0–13.5
     Result: The signature apricot tartness. If you push an apricot to a Ratio of 16, it will completely lose its authenticity and become unrecognizable.

  Why does flavor degrade at Ratio > 15?

  When a fruit overripens on the branch (or when a concentrate is reconstituted incorrectly), two parallel processes occur:

  • Drop in titratable acidity: Organic acids (malic) are broken down during the fruit's respiration.
  • Rise in pH: The decrease in acidity makes the pH rise (toward 4.0 and above).

  At a high pH and a low level of free acids, the tongue's receptors instantly read the taste as «old», «stale», or «chemically sweetened».

• Bostwick viscosity (Bostwick viscosity): A measure of puree consistency, defined as the distance (in cm) that a portion of puree travels along an inclined trough in 30 seconds at a temperature of 20°C. The optimal academic reference is 6–9 cm.
• Color parameter b* (in the colorimetric system CIE L*a*b*): It is measured with a spectrophotometer. A positive b* value characterizes the saturation of the yellow/orange spectrum of the flesh, which is critically important for the visual assessment of peach and apricot purees.

Chapter 9. Palatability Index FPI and incoming quality control of imported raw materials

To digitize the consumer appeal of fruits, tasting panels use the 100-point Fruit Palatability Index (FPI) system.

Classification of FPI scores:

• 90–100 points: Outstanding quality (Premium). Ideal for baby food and premium retail.
• 75–89 points: High commercial quality (Extra Class / Class I). Ideal for retail chains and high-quality NFC juices.
• 55–74 points: Satisfactory quality (Class II). The taste is flat; recommended for industrial jam and fillings.
• Less than 55 points: Unsatisfactory quality. Defective.

Section 10. FAQ: Answers to popular questions about the flavor of fruits

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Conclusion

The taste of an ideal fruit is not a coincidence, but a balance of nature and rigorous science. Relying on the Brix reading, acidity, the BrimA index and the preservation of pulp structure, the professional food industry is able to overcome the «sensory sacrifice» and supply consumers with truly tasty and healthy products.

*The article was prepared by the import analytics department of ANIX based on peer-reviewed research: UNECE standards FFV-50, FFV-26, FFV-02, sensory analysis research of the University of Belgrade (2013), peach biochemistry (MDPI, 2023–2024) and USDA quality standards for fruit and vegetable products.*

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