El descarte de masa madre cambia la hidratación.

Because descarte is a masculine noun in Spanish, so it takes el.

A useful pattern to remember:

• el descarte
• un descarte
• los descartes

Even though some nouns ending in -e can be masculine or feminine, you just have to learn the gender with the word.

In baking, descarte means discard: the portion of sourdough starter you remove instead of feeding or using normally.

So descarte de masa madre is the standard way to say sourdough discard.

This is a specialised baking use of descarte. In more general Spanish, descarte can also mean rejection, elimination, or something ruled out, depending on context.

Spanish often uses de + noun where English uses a noun as an adjective.

So:

• masa madre = sourdough starter
• descarte de masa madre = literally discard of sourdough starter

English can stack nouns very easily: sourdough discard, starter discard, bread dough hydration.
Spanish usually prefers structures with de:

• descarte de masa madre
• hidratación de la masa
• receta de pan

Because Spanish often omits the article after de when the second noun is being used in a classifying sense.

Here, masa madre tells you what kind of discard it is:

• descarte de masa madre = sourdough discard
• harina de trigo = wheat flour
• masa de pizza = pizza dough

If you said del/la masa madre, it would sound more like you were referring to a specific starter already identified in the conversation:

• el descarte de la masa madre que tengo en la nevera

So in the sentence you gave, de masa madre is the normal generic form.

Because the subject is el descarte de masa madre, which is singular.

So the verb must be in the third person singular:

• El descarte ... cambia
• Los descartes ... cambian

Even though masa madre appears after de, it is not the subject. The main noun of the subject is descarte.

Because hidratación is a feminine noun, so it takes la.

In baking, hidratación means hydration level: the proportion of water in relation to flour.

Spanish often uses the definite article where English may use no article or a possessive:

• cambia la hidratación
• literally changes the hydration
• natural English: changes the hydration level

Yes, especially in a baking context, but it can feel a little short or technical.

A slightly fuller version might be:

• El descarte de masa madre cambia la hidratación de la masa.

That version makes it clearer that we mean the hydration of the dough, not just hydration in a vague sense.

Still, your original sentence is understandable and quite natural if the context is already about bread making.

Yes. In Spain, masa madre is the normal and very common term.

Examples:

• hacer pan con masa madre
• alimentar la masa madre
• guardar la masa madre en la nevera

So descarte de masa madre is perfectly appropriate for Spain Spanish.

Yes, but it means something slightly more specific.

• el descarte de masa madre = sourdough discard in general
• el descarte de la masa madre = the discard from the sourdough starter, usually a specific one already known in the conversation

So both are possible, but the version without the article is more general and more label-like.

The word order is very normal for Spanish:

• El descarte de masa madre = the subject
• cambia = the verb
• la hidratación = the direct object

A learner might be tempted to translate English word-for-word in a different way, but this order is the natural Spanish structure: Subject + verb + object

A simple pronunciation guide is:

el dehs-KAR-te de MA-sa MA-dre KAM-bya la ee-dra-ta-THYON

In most of Spain, c before i in hidratación is pronounced like the th in think:

• hidratación → ee-dra-ta-THYON

In Latin America, it would usually sound like s instead:

• ee-dra-ta-SYON

Both are correct for their regions.